WORLD WITH GLOBAL PANDEMIC CORONAVIRUS (Covid-19)

WORLD WITH GLOBAL PANDEMIC  CORONAVIRUS (Covid-19

INTRODUCTION

Over the past 2 decades, coronaviruses (CoVs) have been associated with significant disease outbreaks in East Asia and the Middle East. The severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS) began to emerge in 2002 and 2012, respectively. Recently, a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease 2019 (COVID-19), emerged in late 2019, and it has posed a global health threat, causing an ongoing pandemic in many countries and territories (1). Health workers worldwide are currently making efforts to control further disease outbreaks caused by the novel CoV (originally named 2019-nCoV), which was first identified in Wuhan City, Hubei Province, China, on 12 December 2019. On 11 February 2020, the World Health Organization (WHO) announced the official designation for the current CoV-associated disease to be COVID-19, caused by SARS-CoV-2. The primary cluster of patients was found to be connected with the Huanan South China Seafood Market in Wuhan (2). CoVs belong to the family Coronaviridae (subfamily Coronavirinae), the members of which infect a broad article gives a bird's eye view about this new virus. Since knowledge about this virus is rapidly evolving, readers are urged to update themselves regularly. The 2019 novel Coronavirus (2019 nCov) or the severe acute respiratory syndrome corona virus 2 SARS-Cov-2 as it is now called, is rapidly spreading from its origin in Wuhan city of Hubei, province of China to the rest of the world 1. Till 05/03/2022 around 96000 cases of coronavirus diseases.2019 Covid 19 and 3300 deaths have been reported [2]. India has reported 29 cases till date. Fortunately, so far, children have been infrequently affected with no deaths. But the future course of this virus is unknown.

 

History:

Coronaviruses are enveloped positive sense RNA viruses ranging from 60 nm to 140 nm in diameter with spike like projections on its surface giving it a crown like appearance under the electron microscope: hence the name coronavirus [3]. Four corona viruses namely HKU1, NL63, 229E and OC43 have been in circulation in humans, and generally cause mild respiratory disease. There have been two events in the past two decades wherein crossover of animal betacorona viruses to humans has resulted in severe disease. The first such instance was in 2002-2003 when a of the D was linked to a family member and 26 children had history of travel/residence to Hubei province in China. All the patients were either asymptomatic (9%) or had mild disease. No severe or critical cases were seen. The most common symptoms were fever (50%) and cough (38%). All patients recovered with symptomatic therapy and there were no deaths. One case of severe pneumonia and multiorgan dysfunction in a child has also been reported [19]. Similarly, the neonatal cases that have been reported have been mild [20].

Origin and Spread of COVID-19:

In December 2019, adults in Wuhan, capital city of Hubei province and a major transportation hub of China started presenting to local hospitals with severe pneumonia of unknown cause. Many of the initial cases had a common exposure to the Huanan wholesale seafood market that also traded live animals. The surveillance system (put into place after the SARS outbreak) was activated and respiratory samples of patients were sent to reference labs for etiologic investigations. On December 31st 2019, China notified the outbreak to the World Health Organization and on 1^st January the Huanan sea food market was closed. On 7th January the virus was identified as a coronavirus that had >95% homology with the bat been used based on the experience with SARS and MERS. In a historical control study in patients with SARS, patients treated with lopinavir- ritonavir with ribavirin had better outcomes as compared to those given ribavirin alone [15]. In the case series of 99 hospitalized patients with COVID-19 infection from Wuhan, oxygen was given to 76%, non- invasive ventilation in 13%, mechanical ventilation in 4%, extracorporeal membrane oxygenation (ECMO) in 3%, continuous renal replacement therapy (CRRT) in 9%, antibiotics in 71%, antifungals in 15%, glucocorticoids in 19% and intravenous immunoglobulin therapy in 27% [15]. Antiviral therapy consisting of oseltamivir, ganciclovir and lopinavir- ritonavir was given to 75% of the patients. The duration of non-invasive ventilation was 4-22 d. Cases continued to increase exponentially and modelling studies reported an epidemic doubling time of 1.8 d [10]. In fact on the 12th of February, China changed its definition of confirmed cases to include patients with negative/ pending molecular tests but with clinical, radiologic and epidemiologic features of COVID-19 leading to an increase in cases by 15,000 in a single day [6]. As of 05/03/2020 96,000 cases worldwide (80,000 in China) and 87 other countries and 1 international conveyance (696, in the cruise ship Diamond Princess parked off the coast of Japan) have been reported [2]. It is important to note that while the number of new cases has reduced in China lately, they have increased exponentially in other countries including South Korea, Italy and Iran. of those infected, 20% are in critical condition.

Practice Points from an Indian Perspective: -

 

At the time of writing this article, the risk of coronavirus in India is extremely low. But that may change in the next few weeks. Hence the following is recommended:

•         Healthcare providers should take

            travel history of all patients with

             respiratory symptoms, and any

             international travel in the past 2

             weeks as well as contact with sick

             people who have travelled

              internationally.

•         They should set up a system of

             triage of patients with respiratory

              illness in the outpatient

             department and give them a

              simple surgical mask to wear.

 

•         They should use surgical masks

            themselves while examining such.

             patients and practice hand

             hygiene frequently.

•         Suspected cases should be referred

             to government designated centers

            for isolation and testing (in

            Mumbai, at this time, it is Kasturba.

            hospital). Commercial kits for

            testing is not yet available in

            India.

•         Patients admitted with severe

            pneumonia and acute respiratory

           distress syndrome should be

           evaluated for travel history and

           placed under contact and droplet

            isolation. Regular decontamination of surfaces

            should be done. They should be

            tested for etiology using multiplex

            PCR panels if logistics permit and

            if no pathogen is identified, refer

            the samples for testing for SARS-

            CoV-2.

Epidemiology and Pathogenesis

 

All ages are susceptible. Infection is transmitted through large droplets generated during coughing and sneezing by symptomatic patients but can also occur from asymptomatic people and before onset of symptoms 19]. Studies have shown higher viral locals in the nasal cavity as compared to the throat with no difference in viral burden between symptomatic and asymptomatic people [12]. Patients can be infectious for as long as the symptoms last and even on clinical recovery. Some people may act as super spreaders; a UK citizen who attended a conference in Singapore infected 11 other people while staying in a resort in the French Alps and upon return to the UK [6]. These infected droplets can spread 1-2 m and deposit.

       I.            Diagnosis

Early diagnosis is crucial for controlling the spread of COVID-19. Molecular detection of SARS-CoV-2 nucleic acid is the gold standard. Many viral nucleic acid detection kits targeting ORF1b (including RdRp), N, E or S genes are commercially available11,106-109. The detection time ranges from several minutes to hours depending on the technology106,107,109-111. The molecular detection can be affected by many factors. Although SARS-CoV-2 has been detected from a variety of respiratory sources, including throat swabs, posterior oropharyngeal saliva, nasopharyngeal swabs, sputum and bronchial fluid, the viral load is higher in lower respiratory tract samples. In addition, viral nucleic acid was also found in samples from the intestinal tract or blood even when respiratory samples were negative. Lastly, viral load may already drop from its peak level on disease onset 96,97. Accordingly, false negatives can be common when oral swabs and used, and so multiple detection methods should be adopted to confirm a COVID-19 diagnosis. Other detection methods were there- fore used to overcome this problem. Chest CT was used to quickly identify a patient when the capacity of molecular detection was overloaded in Wuhan. Patients RNA tests can confirm the diagnosis of SARS- CoV-2 (COVID-19) cases with real-time RT-PCR or next-generation sequencing (148, 149, 245, 246). At present, nucleic acid detection techniques, like RT- PCR, are considered an effective method for confirming the diagnosis in clinical cases of COVID- 19 (148). Several companies across the world are currently focusing on developing and marketing SARS-CoV-2-specific nucleic acid detection kits. Multiple laboratories are also developing their own in-house RT-PCR. One of them is the SARS-CoV-2 nucleic acid detection kit produced by Shuoshi Biotechnology (double fluorescence PCR method) (150). Up to 30 March 2020, the U.S. Food and Drug Administration (FDA) had granted 22 in vitro diagnostics Emergency Use Authorizations (EUAs), including for the RT-PCR diagnostic panel for the universal detection of SARS-like betacoronaviruses and specific detection of SARS-CoV-2, developed by the U.S. CDC of persistent local transmission or contact with patients with similar travel history or those with confirmed COVID-19 infection. However cases may be asymptomatic or even without fever. A confirmed case is a suspect case with a positive molecular test.

Specific diagnosis is by specific molecular tests on respiratory samples (throat swab/ nasopharyngeal swab/

sputum/ endotracheal aspirates and bronchoalveolar lavage). Virus may also be detected in the stool and in severe cases, the blood. It must be remembered that the multiplex PCR panels currently available do not include the COVID-19. Commercial tests are also not available at present. In a suspect case in India, the appropriate sample has to be sent to designated reference labs in India or the National Institute of Virology in Pune. As the epidemic progresses, commercial tests.

Differential Diagnosis [21]

The differential diagnosis includes all types of respiratory viral infections [influenza, parainfluenza, respiratory syncytial virus (RSV), adenovirus, human metapneumovirus, non COVID- 19 coronavirus], atypical organisms (mycoplasma, chlamydia) and bacterial infections. It is not possible to differentiate COVID-19 from these infections clinically or through routine’

The differential diagnosis includes all types of respiratory viral infections [influenza, parainfluenza, respiratory syncytial virus (RSV), adenovirus, human metapneumovirus, non COVID- 19 coronavirus], atypical organisms (mycoplasma, chlamydia) and bacterial infections. It is not possible to differentiate COVID-19 from these infections clinically or through routine.

CLINICAL DIAGNOSIS

 

The symptoms of COVID-19 remain very similar to those of the other respiratory epidemics in the past, which include SARS and MERS, but here the range of symptoms includes mild rhinitis to septic shock. Some intestinal disturbances were reported with the other epidemics, but COVID-19 was devoid of such symptoms. When examined, unilateral or bilateral involvement compatible with viral pneumonia is observed in the patients, and bilateral multiple lobular and sub-segmental consolidation areas were observed in patients hospitalize  in the intensive care unit. Comorbid patients showed a more severe clinical course than predicted from previous epidemics. Diagnosis of COVID-19 includes the complete history of travel and touch, with laboratory testing. It is more preferable to choose serological screening, which can help to analyses even the asymptomatic infections; several serological tests are in progress for SARS CoV-2.14, 30

CONVALESCENT PLASMA

THERAPY

Guo Yanhong, an official with the National Health Commission (NHC), stated that convalescent plasma therapy is a significant method for treating severe COVID-19 patients. Among the COVID-19 patients currently receiving convalescent plasma therapy in the virus-hit Wuhan, one has been discharged from hospital, as reported by Chinese science authorities on Monday, 17th February 2020 in Beijing. The first dose of convalescent plasma from a COVID-19 patient was collected on 1^st and 9th February 2020 from a severely ill patient who was given treatment at a hospital in Jiangxia District in Wuhan. The presence of the virus in patients is minimized by the antibodies in the convalescent plasma. Guiqiang stated that donating plasma may cause minimal harm to the donor and that there is nothing to be worried about. Plasma donors must be cured patients and discharged from hospital. Only plasma is used, whereas red blood cells (RBC), white blood cells (WBC) and blood platelets are transfused back into the donor's body. Wang alleged that donor's plasma will totally improve to its initial state after one or 2 weeks from the day of plasma donation of around 200 to 300 mililiters.

Therapeutics

To date, there are no generally proven effective therapies for COVID-19 or antivirals against SARS-CoV-2, although some treatments have shown some benefits in certain subpopulations of patients or for certain end points (see later). Researchers and manufacturers are conducting large-scale clinical trials to evaluate various therapies for COVID-19. As of 2 October 2020, there were about 405 therapeutic drugs in development for COVID-19, and nearly 318 in human clinical trials (COVID-19 vaccine and therapeutics tracker). In the following sections, we summarize potential therapeutics against SARS-CoV-2 on the basis of published clinical data and experience. in vitro and in vivo. Compared with convalescent plasma, which has limited availability and cannot be amplified, monoclonal antibodies can be developed in larger quantities to meet clinical requirements. Hence, they provide the possibility for the treatment and prevention of COVID-19. The neutralizing epitopes of these monoclonal antibodies also offer important information for vaccine design. However, the high cost and limited capacity of manufacturing, as well as the problem of bioavailability, may restrict the wide application of monoclonal antibody therapy.

Coronaviruses in Humans SARSMERS and COVID-19

Coronavirus infection in humans is commonly associated with mild to severe respiratory diseases, with high fever, severe inflammation, cough, and internal organ dysfunction that can even lead to death (92). Most of the identified coronaviruses cause the common cold in humans. However, this changed when SARS-CoV was identified, paving the way for severe forms of the disease in humans (22). Our previous experience with the outbreaks of other coronaviruses, like SARS and MERS, suggests that the mode of transmission in COVID-19 as mainly human-to-human transmission via direct contact, droplets, and fomites (25). Recent studies have demonstrated that the virus could remain viable for hours in aerosols and up to days on surfaces, thus, aerosol and fomite contamination could play potent roles in the transmission of SARS-CoV-2 . The immune response against coronavirus is vital to control and get rid of the infection. However, maladjusted immune responses may contribute to the resulting immunopathology of the disease, in impairment of pulmonary gas exchange. Understanding the interaction between CoVs and host innate immune systems could enlighten our aminotransferase, bilirubin, and, especially, D-dimer. Middle-aged and elderly patients with primary chronic diseases, especially high blood pressure and diabetes, were found to be more susceptible to respiratory failure and, therefore, had poorer prognoses. Providing respiratory support at early stages improved the disease prognosis and facilitated recovery (18). The ARDS in COVID-19 is due to the occurrence of cytokine storms that results in exaggerated immune response, immune regulatory network imbalance, and, finally, multiple-organ. failure (122). In addition to the exaggerated inflammatory response seen in patients with COVID-19 pneumonia, the bile duct epithelial cell- derived hepatocytes upregulate ACE2 expression in liver tissue by compensatory proliferation that might result in hepatic tissue injury.

CORONAVIRUSES IN ANIMALS AND

ZOONOTIC LINKS A BRIEF

o   VIEWPOINT

Coronavirus can cause disease in several species of domestic and wild animals, as well as humans (23). The different animal species that are infected with CoV include horses, camels, cattle, swine, dogs, cats, rodents, birds, ferrets, minks, bats, rabbits, snakes, and various other wild animals. Hence, knowledge and understanding of S protein-based vaccine development in SARS-CoV will help to identify potential S protein vaccine candidates in SARS CoV-2. Therefore, vaccine strategies based on the whole S protein, S protein subunits, or specific potential epitopes of S protein appear to be the most promising vaccine candidates against coronaviruses. The RBD of the S1 subunit of S protein has a superior capacity to induce neutralizing antibodies. This property of the RBD can be utilized for designing potential SARS-CoV vaccines either by using RBD-containing recombinant proteins or recombinant vectors that encode RBD (175). Hence, the superior genetic similarity existing between SARS-CoV-2 and SARS- CoV can be utilized to repurpose vaccines that have proven in vitro efficacy against SARS-CoV to be utilized for SARS-CoV-2. The possibility of cross- protection in COVID-19 was evaluated by comparing the S protein sequences of SARS-CoV-2 with that of SARS-CoV. The comparative analysis confirmed that the variable residues were found concentrated on the S1 subunit of S protein, an important vaccine target of the virus (150). Hence, the possibility of SARS-CoV-specific neutralizing antibodies providing cross-protection to COVID-19 might be lower. Further genetic analysis is required:

 

Infections:

 

·          SARS is a viral respiratory disease caused by a

             formerly unrecognized animal CoV that originated

             from the wet markets in southern China after

              adapting to the human host, thereby enabling

             transmission between humans (90). The SARS

             outbreak reported in 2002 to 2003 had 8,098

              confirmed cases with 774 total deaths (9.6%) (93).

·         The outbreak severely affected the Asia Pacific

            region, especially mainland China (94). Even though

            the case fatality rate (CFR) of SARS-CoV-2

            (COVID-19) is lower than that of SARS-CoV, there

             exists a severe concern linked to this outbreak due to

             its epidemiological similarity to influenza viruses

             (95, 279). This can fail the public health system,

              resulting in a pandemic (96).

.

·         MERS is another respiratory disease that was

            first reported in Saudi Arabia during the year 2012.

           The disease was found to have a CFR of around 35%

            (97). The analysis of available data sets suggests that

           the incubation period of SARS-CoV-2, SARS-CoV,

           and MERS-CoV is in almost the same range. The

            longest predicted incubation time of SARS-CoV-2 is

           14 days. Hence, suspected individuals are isolated

           for 14 days to avoid the risk of further spread (98).

          Even though a high similarity has been reported.

PROTEINS:-

 

1.      N Protein

The N protein of coronavirus is multipurpose.

Among several functions, it plays a role in complex

formation with the viral genome, facilitates M

protein interaction needed during virion assembly,

and enhances the transcription efficiency of the virus

(55, 56). It contains three highly conserved and

distinct domains, namely, an NTD, an RNA-binding

domain or a linker region (LKR), and a CTD (57).

The NTD binds with the 3' end of the viral genome,

perhaps via electrostatic interactions, and is highly

diverged both in length and sequence. The

charged LKR is serine and arginine rich and is also

known as the SR (serine and arginine) domain.

The LKR is capable of direct interaction with in vitro

RNA interaction and is responsible for cell signaling

(60, 61). It also modulates the antiviral response of

the host by working as an antagonist for interferon

(IFN) and RNA interference (62). Compared to that

of SARS-CoV, the N protein of SARS-CoV-2

possess five amino acid mutations, where two are in

the intrinsically dispersed region (IDR; positions 25

and 26), one each in the NTD (position 103), LKR

(position 217), and CTD.

2.      M Protein

 

The M protein is the most abundant viral protein

present in the virion particle, giving a definite shape

to the viral envelope (48). It binds to the

nucleo capsid and acts as a central organizer of

coronavirus assembly (49). Coronavirus M proteins

are highly diverse in amino acid contents but

maintain overall structural similarity within different

genera (50). The M protein has three transmembrane

domains, flanked by a short amino terminus outside

the virion and a long carboxy terminus inside the

virion (50). Overall, the viral scaffold is maintained

by M-M interaction. Of note, the M protein of

SARS-CoV-2 does not have an amino

acid

substitution compared to that of SARS-CoV (16).

 

3.      •E Protein

 

The coronavirus E protein is the most enigmatic

and smallest of the major structural proteins (51). It

plays a multifunctional role in the pathogenesis,

assembly, and release of the virus (52). It is a small

integral membrane polypeptide that acts as a

viroporin.

Animal host and spillover:

 

Bats are important natural hosts of alphacoronavi- ruses and betacoronaviruses. The closest relative to SARS-CoV-2 known to date is a bat coronavirus detected in Rhinolophus affinis from Yunnan province, China, named 'RaTG13', whose full-length genome sequence is 96.2% identical to that of SARS-CoV-2 (REF.¹). This bat virus shares more than 90% sequence identity with SARS-CoV-2 in all ORFs throughout the genome, including the highly variable S and ORF8 (REF.¹). Phylogenetic analysis confirms that SARS-CoV-2closely clusters with RaTG13 (FIG. 2). The high genetic similarity between SARS-CoV-2 and RaTG13 supports the hypothesis that SARS-CoV-2 likely originated from bats 35. Another related coronavirus has been reported more recently in a Rhinolophus malayanus bat sampled in Yunnan This novel hat virus denoted 'RmYN02' 

 

Viewpoint on SARS-CoV-2 Transmission,

Spread, and Emergence:

The novel coronavirus was identified within 1 month (28 days) of the outbreak. This is impressively fast compared to the time taken to identify SARS-CoV reported in Foshan, Guangdong Province, China (125 days) (68). Immediately after the confirmation of viral etiology, the Chinese virologists rapidly released the genomic sequence of SARS-CoV-2, which played  a crucial role in controlling the spread of this newly emerged novel coronavirus to other parts of the world (69). The possible origin of SARS-CoV-2 and the first mode of antiviral drugs Repurposed broad-spectrum having proven uses against other viral pathogens can be employed for SARS-CoV-2-infected patients. These possess benefits of easy accessibility and recognized pharmacokinetic and pharmacodynamics activities, stability, doses, and side effects (9). Repurposed drugs have been studied for treating COV infections, like lopinavir/ritonavir, and Interferon-13 revealed in vitro anti-MERS-CoVaction. The in vivo experiment carried out in the nonhuman primate model of common marmosets treated with lopinavir/ritonavir and interferon beta showed superior protective results in treated animals than in the untreated ones (190). A combination of these drugs is being evaluated to treat MERS in humans (MIRACLE trial) (191). These two protease inhibitors:

·         lopinavir

·          ritonavir

 In combination with ribavirin, gave encouraging clinical outcomes in SARS patients, suggesting their therapeutic values (165). However, in the current scenario, due to the lack of specific therapeutic agents against SARS- CoV-2, hospitalized patients confirmed for the disease are given supportive care, like oxygen and fluid therapy, along with antibiotic therapy for managing secondary bacterial infections (192). Patients with novel coronavirus or COVID-19 pneumonia who are mechanically ventilated often require sedatives. analgesics. and even muscle system (30). Bovine coronaviruses (BoCoVs) are known to infect several domestic and wild ruminants (126). BoCoV inflicts neonatal calf diarrhea in adult cattle, leading to bloody diarrhea (winter dysentery) and respiratory disease complex (shipping fever) in cattle of all age groups (126). BoCoV-like viruses have been noted in humans, suggesting its zoonotic potential as well (127). Feline enteric and feline infectious peritonitis (FIP) viruses are the two major feline CoVs (128), where feline CoVs can affect the gastrointestinal tract, abdominal cavity (peritonitis), respiratory tract, and central nervous system (128). Canines are also affected by CoVs that fall under different genera, namely, canine enteric coronavirus in Alpha coronavirus and canine respiratory coronavirus in Beta coronavirus, affecting the enteric and respiratory tract, respectively (129, 130). IBV, under Gamma coronavirus, causes diseases of respiratory, urinary, and reproductive systems, with substantial economic losses in chickens (131, 132). In small laboratory animals, mouse hepatitis virus, rat sialoda cryoadenitis coronavirus, and guinea pig and rabbit coronaviruses are the major CoVs associated with disease manifestations like enteritis, hepatitis, and respiratory infections (10, 133). Swine acute diarrhea syndrome coronavirus residues for receptor binding 40 (FIG. 3b). In comparison with the Guangdong strains, pangolin coronaviruses reported from Guangxi are less similar to SARS-CoV-2, with 85.5% genome sequence identity. The repeated occurrence of SARS-CoV-2-related coronavirus infections in pangolins from different smuggling events suggests that these animals are possible hosts of the viruses. However, unlike bats, which carry coronaviruses healthily, the infected pangolins showed clinical signs and histopathological changes, including interstitial pneumonia and inflammatory cell infiltration in diverse organs40. These abnormalities suggest that pangolins are unlikely to be the reservoir of these coronaviruses but more likely acquired the viruses after spillover from the natural hosts. An intermediate host usually plays an important role in the outbreak of bat-derived emerging coronaviruses; for example, palm civets for SARS-CoV and dromedary camels for MERS-CoV. The virus strains carried by these two intermediate hosts were almost genetically identical to the corresponding viruses in humans (more than 99% genome sequence identity)¹. Despise an RBD that is virtually identical to that of SARS-CoV-2, the pangolin coronaviruses known to date have no more than 92% genome identity with SARS-CoV-2 (REF. 42). The avail- able data are insufficient to interpret pangolins as the intermediate host of SARS-CoV-2. So far, no evidence has shown that pangolins were directly involved in the emergence of SARS-CoV-2. that remdesivir has to be further evaluated for its efficacy in the treatment of COVID-19 infection in humans. The broad-spectrum activity exhibited by remdesivir will help control the spread of disease in the event of a new coronavirus outbreak. Chloroquine is an antimalarial drug known to possess antiviral activity due to its ability to block virus-cell fusion by raising the endosomal pH necessary for fusion. It also interferes with virus- receptor binding by interfering with the terminal glycosylation of SARS-CoV cellular receptors, such as ACE2 (196). In a recent multicenter clinical trial that was conducted in China, chloroquine phosphate was found to exhibit both efficacy and safety in the therapeutic management of SARS-CoV-2-associated pneumonia (197). This drug is already included in the treatment guidelines issued by the National

 Health Commission of the People's Republic of China. The preliminary clinical trials using hydroxyl-chloroquine, another amino-quinoline drug, gave promising results. The COVID-19 patients received 600 mg of hydroxyl-chloroquine daily along with azithromycin as a single-arm protocol. This protocol was found to be associated with a noteworthy reduction in viral load. Finally, it resulted in a complete cure (271); however, the study co All of these therapeutic

approaches have revealed both in vitro and in vivo anti-CoV potential. Although in vitro research carried out with these therapeutics showed efficacy, most need appropriate support from randomized animal or human trials. Therefore, they might be of limited applicability and require trials against SARS-CoV-2 to gain practical usefulness. The binding of SARS-CoV-2 with ACE2 leads to the exacerbation of pneumonia as a consequence of the imbalance in the renin- angiotensin system (RAS). The virus-induced pulmonary inflammatory responses may be reduced by the administration of ACE inhibitors (ACEI) and angiotensin type-1 receptor (AT1R) (207). Several investigations have suggested the use of small-molecule inhibitors for the potential control of SARS-CoV infections. Drugs of the FDA-approved compound library were screened to identify four small-molecule inhibitors of MERS-CoV (chlorpromazine, chloroquine, loperamide, and lopinavir) that inhibited viral replication. These compounds also hinder SARS CoV and human CoVs (208). Therapeutic strategies involving the use of specific antibodies or compounds that neutralize cytokines and their receptors will help to restrain the host inflammatory responses. Such drugs acting specifically in the respiratory tract will help toprise a small population and, hence, the major problem associated with this diagnostic kit is that it works only when the test subject has an active infection, limiting its use to the earlier stages of infection. Several laboratories around the world are currently developing antibody-based diagnostic tests against SARS-CoV-2 (157).  Chest CT is an ideal diagnostic tool for identifying viral pneumonia. The sensitivity of chest CT is far superior to that of X-ray screening. The chest CT findings associated with COVID-19- infected patients include characteristic patchy infiltration that later progresses to ground-glass opacities (158). Early manifestations of COVID-19 pneumonia might not be evident in X-ray chest radiography. In such situations, a chest CT examination can be performed, as it is considered highly specific for COVID-19 pneumonia (118). Those patients having COVID-19 pneumonia will exhibit the typical ground-glass opacity in their chest CT images (154). The patients infected with COVID-19 had elevated plasma angiotensin 2 levels. The level of angiotensin 2 was found to be linearly associated with viral load and lung injury, indicating its potential as a diagnostic biomarker (121). The chest CT imaging abnormalities associated with COVID-19 pneumonia have also been observed even in asymptomatic patients. and ritonavir had little therapeutic benefit in patients with COVID-19, but appeared more effective when used in combination with other drugs, including ribavirin and interferon beta-lb143,144. The Randomized Evaluation of COVID-19 Therapy (RECOVERY) trial, a national clinical trial programme in the UK, has stopped treatment with lopinavir and ritonavir as no significant beneficial

 was observed in a randomized trial established in March 2020 with a total of 1,596 patients ¹45. Nevertheless,

 respiratory syncytial virus, rhinovirus, human meta-pneumo virus and SARS coronavirus. It is advisable to distinguish COVID-19 from other pneumonias such as mycoplasma pneumonia, chlamydia pneumonia and bacterial pneumonia.33 Several published pieces of literature based on the novel coronavirus reported in China declared that stool and blood samples can also collected from the suspected persons in order to detect the virus. However, respiratory samples show better viability in identifying the virus, in comparison with the other specimens. 34-36.  SARS-CoV-2 uses ACE2 as the receptor and human proteases as entry activators; sub- sequently it fuses the viral membrane with the cell mem- brane and achieves invasion. Thus, drugs that interfere with entry may be a potential treatment for COVID-19. Umifenovir (Arbidol) is a drug approved in Russia and China for the treatment of influenza and other respiratory viral infections. It can target the interaction between. the S protein and ACE2 and inhibit membrane fusion. In vitro experiments showed that it has activity against SARS-CoV-2, and current clinical data revealed it may be more effective than lopinavir and ritonavir in treating COVID-19 (REFS 122,123). However, other clinical studies showed umifenovir might not improve the prognosis of or accelerate SARS-CoV-2 clearance in patients with mild to moderate COVID-19 (REFS124,125). Yet some ongoing clinical trials are evaluating its efficacy for COVID-19 treatment. Camostat mesylate is approved. in Japan for the treatment of pancreatitis and postoperative reflux oesophagitis. Previous studies showed that it can prevent SARS-CoV from entering cells by blocking TMPRSS2 activity and protect mice from lethal infection with SARS-CoV in a pathogenic mouse model (wild- type mice infected with a mouse-adapted SARS-CoV strain) 126,127. Recently, a study revealed that camo-statmesylate blocks the entry of SARS-CoV-2 into human lung cells 47. Thus, it can be a potential antiviral drug against SARS-CoV-2 infection, although so far there are not sufficient clinical data to support its efficacy.

 

CURRENT WORLDWIDE SCENARIO OF

SARS-CoV-2:

 This novel virus, SARS-CoV-2, comes under the subgenus Sarbecovirus of the Orthocoronavirinae subfamily and is entirely different from the viruses developed for rapid and colorimetric detection of this virus (354). RT-LAMP serves as a simple, rapid, and sensitive diagnostic method that does not require so phisticated equipment or skilled personnel (349). An interactive web-based dashboard for tracking SARS-CoV-2 in a real-time mode has been designed (238). A smartphone-integrated home-based point- of-care testing (POCT) tool, a paper-based POCT combined with LAMP, is a useful point-of-care diagnostic (353). An Abbott ID Now COVID-19 molecular POCT-based test, using isothermal nucleic acid amplification technology, has been designed as point-of-care test for very rapid detection of SARS-CoV-2 in just 5 min (344). A CRISPR-based SHERLOCK (specific high-sensitivity enzymatic reporter unlocking) diagnostic for rapid detection of SARS-CoV-2 without the requirement of specialized instrumentation has been reported to be very useful in the clinical diagnosis of COVID-19 (360). A CRISPR-Cas12-based lateral flow assay also has been developed for rapid detection of SARS-CoV-2 (346). Artificial intelligence, by means of a three- dimensional deep-learning model, has been developed for sensitive and specific diagnosis of COVID-19 via CT images (332).

Splits Tree phylogeny analysis:

 

In the unrooted phylogenetic tree of different betacoronaviruses based on the S protein, virus sequences from different subgenera grouped into separate clusters. SARS-CoV-2 sequences from Wuhan and other countries exhibited a close relationship and appeared in a single cluster (Fig. 1). The CoVs from the subgenus Sarbecovirus appeared jointly in Splits Tree and divided into three subclusters, namely, SARS-CoV-2, bat-SARS-like- CoV (bat-SL-CoV), and SARS-CoV (Fig. 1). In the case of other subgenera, like Merbecovirus, all of the sequences grouped in a single cluster, whereas in Embecovirus, different species, comprised of canine respiratory CoVs, bovine CoVs, equine CoVs, and human CoV strain (OC43), grouped in a common cluster. Isolates in the subgenera Nobecovorus and Hibecovirus were found to be placed separately away from other reported SARS-CoVs but shared a bat origin. prevent further spread of disease at mass gatherings, functions remain canceled in the affected cities, and persons are asked to work from home (232). Hence, it is a relief that the current outbreak of COVID-19 infection can be brought under control with the adoption of strategic preventive and control measures along with the early isolation of subsequent cases in the coming days. Studies also report that since air traffic between China and African countries increased many times over in the decade after the SARS outbreak, African countries need to be vigilant to prevent the spread of novel coronavirus in Africa (225). Due to fear of virus spread, Wuhan City was completely shut down (233). The immediate control of the ongoing COVID-19 outbreaks appears a mammoth task, especially for developing countries, due to their Inability to allocate quarantine stations that could screen infected individuals' movements (234). Such underdeveloped countries should divert their resources and energy to enforcing the primary level of preventive measures, like controlling the entry of individuals from China or countries where the disease has flared up, isolating the infected individuals, and quarantining individuals with suspected infection. Most of the sub-Saharan African countries have a fragile health system that can be (using suitable animal models) should be conducted to evaluate the risk of future epidemics. Presently, licensed antiviral drugs or vaccines against SARS- CoV, MERS-CoV, and SARS-CoV-2 are lacking. However, advances in designing antiviral drugs and vaccines against several other emerging diseases will help develop suitable therapeutic agents against COVID-19 in a short time. Until then, we must rely exclusively on various control and prevention measures to prevent this new disease from becoming a pandemic.

 

PREVENTION:-

The WHO and other agencies such as the CDC have published protective measures to mitigate the spread of COVID-19. This involves frequent hand washing with hand wash containing 60% of alcohol and soap for at least 20 seconds. Another important measure is avoiding close contact with sick people and keeping a social distance of 1 metre always to everyone who is coughing and sneezing. Not touching the nose, eyes and mouth was also suggested. While coughing or sneezing, covering the mouth and nose with a cloth/tissue or the bent elbow is advised. Staying at home is recommended for those who are sick, and wearing a facial mask is advised when going out among people. Furthermore, it is recommended to clean and sterilize frequently touched surfaces such as phones and doorknobs on a daily basis. 51, 52 Staying at home as much as possible is advisable for those who are at higher risk for severe illness, to minimize the risk of exposure to COVID-19 during outbreaks.53 Since at this time there are no approved treatments for this infection, prevention is crucial. Several properties of this virus make prevention difficult namely, non- specific features of the disease, the infectivity even before onset of symptoms in the incubation period, transmission from asymptomatic people, long incubation period, tropism for mucosal surfaces such as the conjunctiva, prolonged duration of the illness and transmission even after clinical recovery. Isolation of confirmed or suspected cases with mild illness at home is recommended. The ventilation at home should be good with sunlight to allow for destruction of virus. Patients should be asked to wear a simple surgical mask and practice cough hygiene. In contrast to their response to the 2002 SARS outbreak, China has shown immense political openness in reporting the COVID-19 outbreak promptly. They have also performed rapid sequencing of COVID-19 at multiple levels and shared the findings globally within days of identifying the novel virus (225). The move made by China opened a new chapter in global health security and diplomacy. Even though complete lockdown was declared following the COVID-19 outbreak in Wuhan, the large-scale movement of people has resulted in a radiating spread of infections in the surrounding provinces as well as to several other countries. dogs have low susceptibility, while the chickens, ducks, and pigs are not at all susceptible to SARS- CoV-2 (329). Similarly, the National Veterinary Services Laboratories of the USDA have reported COVID-19 in tigers and lions that exhibited respiratory signs like dry cough and wheezing. The zoo animals are suspected to have been infected by an asymptomatic zookeeper (335). The total number of COVID-19- positive cases in human beings is increasing at a high rate, thereby creating ideal conditions for viral spillover to other species, such as pigs. The evidence obtained from SARS-CoV suggests that pigs can get infected with SARS-CoV-2 (336). However, experimental inoculation with SARS-CoV-2 failed to infect pigs (329). Further studies are required to identify the possible animal reservoirs of SARS-CoV-2 and the seasonal variation in the circulation of these viruses in the animal population. Research collaboration between human and animal health sectors is becoming a necessity to evaluate and identify the possible risk factors of transmission between animals and humans. Such cooperation will help to devise efficient strategies for the management of emerging zoonotic diseases (12). vitro antiviral potential of FAD-approved drugs, viz., ribavirin, penciclovir, nitazoxanide, nafamostat, and chloroquine, tested in comparison to remdesivir and favipiravir (broad-spectrum antiviral drugs) revealed remdesivir and chloroquine to be highly effective against SARS-CoV-2 infection in vitro (194). Ribavirin, penciclovir, and favipiravir might not possess noteworthy in vivo antiviral actions for SARS-CoV-2, since higher concentrations of these nucleoside analogs are needed in vitro to lessen the viral infection. Both remdesivir and chloroquine are being used in humans to reat other diseases, and such safer drugs can be explored for assessing their effectiveness in COVID-19 patients. Several therapeutic agents, such as lopinavir/ritonavir, chloroquine, and hydroxychloroquine, have been proposed for the clinical management of COVID-19 (299). A

molecular docking study, conducted in the RNA- dependent RNA polymerase (RdRp) of SARS-CoV-2 using different commercially available antipolymerase drugs, identified that drugs such as

ribavirin, remdesivir, galidesivir, tenofovir, and sofosbuvir bind RdRp tightly, indicating their vast potential to be used against COVID-19 (305). A broad-spectrum antiviral drug that was developed in US. high commercial value, since they are used in traditional Chinese medicine (TCM). Therefore, the handling of bats for trading purposes poses a considerable risk of transmitting zoonotic CoV epidemics (139). Due to the possible role played by farm and wild animals in SARS-CoV-2 infection, the WHO, in their novel coronavirus (COVID-19) situation report, recommended the avoidance of unprotected contact with both farm and wild animals (25). The live- animal markets, like the one in Guangdong, China, provides a setting for animal coronaviruses to amplify and to be transmitted to new hosts, like humans (78). Such markets can be considered a critical place for the origin of novel zoonotic diseases and have enormous public health significance in the event of an outbreak. Bats are the reservoirs for several viruses; hence, the role of bats in the present outbreak cannot be ruled out (140). In a qualitative study conducted for evaluating the zoonotic risk factors among rural communities of southern China, the frequent human-animal interactions along with the low levels of environmental biosecurity were identified as significant risks for the emergence of zoonotic disease in local communities (141, 142). the United States, tilorone di-hydrochloride (tilorone), was previously found to possess potent antiviral activity against MERS, Marburg, Ebola, and Chikungunya viruses (306). Even though it had broad-spectrum activity, it was neglected for an extended period. Tilorone is another antiviral drug that might have activity against SARS-CoV-2. Remdesivir, a novel nucleotide analog prodrug, was developed for treating Ebola virus disease (EVD), and it was also found to inhibit the replication of SARS-CoV and MERS-CoV in primary human airway epithelial cell culture systems (195). Recently, in vitro study has proven that remdesivir has better antiviral activity than lopinavir and ritonavir. Further, in vivo studies conducted in mice also identified that treatment with remdesivir improved pulmonary function and reduced viral loads and lung pathology both in prophylactic and therapeutic regimens

to compared lopinavir/ritonavir-IFN-y treatment in MERS-CoV infection (8). Remdesivir also inhibits a diverse range of coronaviruses, including circulating human CoV, zoonotic bat CoV, and prepandemic zoonotic CoV (195). Remdesivir is also considered the only therapeutic drug that significantly reduces pulmonary pathology (8). All these findings indicate that remdesivir has to be further evaluated for its specifically in the respiratory tract will help to reduce virus-triggered immune pathologies in COVID-19 (209). The later stages of coronavirus- induced inflammatory cascades are characterized by the release of pro inflammatory interleukin-1 family members, such as IL-1 and IL-33. Hence, there exists a possibility that the inflammation associated with coronavirus can be inhibited by utilizing anti-inflammatory cytokines that belong to the IL-1 family (92). It has also been suggested that the actin protein is the host factor that is involved in cell entry and pathogenesis of SARS-CoV-2. Hence, those drugs that modulate the biological activity of this protein, like ibuprofen, might have some therapeutic application in managing the disease (174). The plasma angiotensin 2 level was found to be markedly elevated in COVID-19 infection and was correlated with viral load and lung injury. Hence, drugs that block angiotensin receptors may have potential for treating COVID-19 infection (121). A scientist from Germany, named Rolf Hilgenfeld, has been working on the identification of drugs for the treatment of coronaviral infection since the time of the first SARS outbreak (19).

Laboratory testing for coronavirus disease 2019 (COVID-

19) in suspected human cases

 

The assessment of the patients with COVID-19 should be based on the clinical features and also epidemiological factors. The screening protocols must be prepared and followed per the native context.31 Collecting and testing of specimen samples from the suspected individual is considered to be one of the main principles for controlling and managing the outbreak of the disease in a country. The suspected cases must be screened thoroughly in order to detect the virus with the help of nucleic acid amplification tests such as reverse transcription polymerase chain reaction (RT- PCR). If a country or a particular region does not have the facility to test the specimens, the specimens of the suspected individual should be sent to the nearest reference laboratories per the list provided by WHO.32 It is also recommended that the suspected patients be tested for the other respiratory pathogens by performing the routine laboratory investigation per the local guidelines, mainly to differentiate from other viruses that include  influenza virus, parainfluenza virus, adenovirus, respiratory syncytial virus, rhinovirus, human there, there is an increase in the outbreak of this virus through human-to-human transmission, with the fact that it has become widespread around the globe. This confirms the fact similar to the previous epidemics, including SARS and MERS, that this coronavirus exhibited potential human-to-human transmission, as it was recently declared a pandemic by WHO.26 Respiratory droplets are the major carrier for coronavirus transmission. Such droplets can either stay in the nose or mouth or enter the lungs via the inhaled air. Currently, it is known that COVID-19's transmission from one person to another also occurs through touching either an infected surface or even an object. With the current scant awareness of the transmission systems however, airborne safety measures with a high-risk procedure have been proposed in many countries. Transmission levels, or the rates from one person to another, reported differ by both location and interaction with involvement in infection control. It is stated that even asymptomatic individuals or those

individuals in their incubation period can act as carrier of SARS-CoV2.27, 28 With the data and evidence provided by the CDC, the usual incubation period is probably 3 to 7 days, sometimes being prolonged up to even 2 weeks, and the typical symptom occurrence.

Inhibition of virus replication:

 

Replication inhibitors include remdesivir (GS-5734), favilavir (T-705), riba- virin, lopinavir and ritonavir. Except for lopinavir and ritonavir, which inhibit 3CLpro, the other three all target RdRp128,135 (FIG. 5). Remdesivir has shown activity against SARS-CoV-2 in vitro and in vivo ¹28,136. A clinical study revealed a lower need for oxygen support in patients with COVID-19 (REF.137). Preliminary results of the Adaptive COVID-19 Treatment Trial (ACTT) clinicaltrial by the National Institute of Allergy and Infectious Diseases (NIAID) reported that remdesivir can shorten the recovery time in hospitalized adults with COVID-19 by a couple days compared with placebo, but the differ- once in mortality was not statistically significant¹3³8. The FDA has issued an emergency use authorization for rem- desivir for the treatment of hospitalized patients with severe COVID-19. It is also the first approved option by the European Union for treatment of adults and adolescents with pneumonia requiring supplemental oxygen. Several international phase III clinical trials are contin- using to evaluate the safety and efficacy of remdesivir for the treatment of COVID-19. Favilavir (T-705), which is an antiviral drug developed in Japan to treat influenza, has been approved in China, Russia and India for the treatment of COVID-19. A clinical study in China showed that favilavir significantly reduced the signs of improved disease signs on chest imaging and shortened the time to viral clearance¹39. A preliminary report in Japan showed rates of clinical improvement of 73.8% and 87.8% from the start of favilavir therapy in patients with mild COVID-19 at 7 and 14 days, respectively, and 40.1% and 60.3% 

in patients with severe COVID-19 at 7 and 14 days, severe illness, to minimize the risk of exposure to COVID-19 during outbreaks.53.

VACCINES

The strange coronavirus outbreak in the Chinese city of Wuhan, now termed COVID-19, and its rapid transmission, threatens people around the world. Because of its pandemic nature, the National Institutes of Health (NIH) and pharmaceutical companies are involved in the development of COVID-19 vaccines. Xu Nanping, China's vice-minister of science and technology, announced that the first vaccine is expected to be ready for clinical trials in China at the end of April 2020.54 There is no approved vaccine and treatment for COVID-19 infections. Vaccine development is sponsored and supported by the Biomedical Advanced Research and Development Authority (BARDA), a component of the Office of the Assistant Secretary for Preparedness and Response (ASPR). Sanofi will use its egg-free, recombinant DNA technology to produce an exact genetic match to proteins of the virus.55. and other SARSr-CoVs (FIG. 2). Using sequences of five conserved replicative domains in pplab (3C-like protease (3CLpro), nidovirus RNA-dependent RNA polymerase (RdRp)-associated nucleotidy ltransferase (NiRAN), , zinc-binding domain (ZBD) and HEL1), the Coronaviridae Study Group of the International Committee on Taxonomy of Viruses estimated the pairwise patristic distances between SARS-CoV-2 and known coronaviruses, and assigned SARS-CoV-2 to the existing species SARSr-CoV¹7. Although phylogenetically related, SARS-CoV-2 is distinct from all other coronaviruses from bats and pangolins in this species. The SARS-CoV-2 S protein has a full size of 1,273 amino acids, longer than that of SARS-CoV (1,255 amino acids) and known bat SARS-CoVs (1,245-1,269 amino acids). It is distinct from the S proteins of most members in the subgenus Sarbecovirus, sharing amino acid sequence similarities of 76.7- 77.0% with SARS-CoVs from civets and humans, Vaccination is the most effective method for a long-term strategy for prevention and control of COVID-19 in the future. Many different vaccine platforms against SARS-CoV-2 are in development, the strategies of which include recombinant vectors, DNA, mRNA in lipid nanoparticles, inactivated viruses, live attenuated viruses and protein subunits ¹59-161. As of 2 October 2020, ~174 vaccine candidates for COVID-19 had been reported and 51 were in human clinical trials (COVID-19 vaccine and therapeutics tracker). Many of these vaccine candidates are in phase II testing, and some have already advanced to phase III trials. A randomized double-blinded phase II trial of an adenovirus type vectored vaccine expressing the SARS-CoV-2 S protein, developed by Can Sino Biologicals and the Academy of Military Medical Sciences of China, was conducted in 603 adult volunteers in Wuhan. The vaccine has proved to be safe and induced considerable humoral and cellular immune response in most recipients after a single immunization ¹62. Another vectored vaccine, ChAdOx1 been controlled by adopting appropriate and strict prevention and control measures, and patients for clinical trials will not be available. The newly developed drugs cannot be marketed due to the lack of end users. The S protein plays a significant role in the induction of protective immunity against SARS-CoV by mediating T-cell responses and neutralizing antibody production (168). In the past few decades,

we have seen several attempts to develop a vaccine against human coronaviruses by using S protein as the target (168, 169). However, the developed vaccines have minimal application, even among closely related strains of the virus, due to a lack of cross-protection. That is mainly because of the extensive diversity existing among the different antigenic variants of the virus (104). The contributions of the structural proteins, like spike (S), matrix (M), small envelope (E), and nucleocapsid (N) proteins, of SARS-CoV to induce protective immunity has been evaluated by expressing them in a recombinant parainfluenza virus type 3 vector (BHPIV3). Of note, the result was conclusive that the expression of M, E, or N proteins without the presence of S protein would not.

RECOMBINANT SUBUNIT

VACCINE

Clover Biopharmaceuticals is producing a recombinant subunit vaccine based on the trimeric S-protein of COVID-19.55 The oral recombinant vaccine is being expanded by Vaxart in tablet formulation, using its proprietary oral vaccine platform.

 

TREATMENT:

In severe COVID-19 cases, treatment should be given to support vital organ functions. People who think they may have been exposed to COVID-19 should contact their healthcare provider immediately. Healthcare personnel should care for patients in an Airborne Infection Isolation Room (AIIR). Precautions must be taken by the healthcare professional, such as contact precautions and airborne precautions with eye protection S 56 Individuals with a mild clinical presentation may not require primary hospitalization. Close monitoring is needed for the persons infected with COVID-19. Elderly patients and those with prevailing chronic medical conditions such as   rates, disease outbreaks, community spread, clustered transmission events, hot spots, and super spreader potential of SARS-CoV-2/COVID warrant full exploitation of real-time disease mapping by employing geographical information systems (GIS), such as the GIS software Kosmo 3.1, web-based real-time tools and dashboards, apps, and advances in information technology (356-359). Researchers have also developed a few prediction tools/models, such as the prediction model risk of bias assessment tool (PROBAST) and critical appraisal and data extraction for systematic reviews of prediction modeling studies (CHARMS), which could aid in assessing the possibility of getting infection and estimating the prognosis in patients; however, such models may suffer from bias issues. and, hence, cannot be considered completely trustworthy, which necessitates the development of new and reliable predictors (360). Recently emerged viruses, such as Zika, Ebola, and Nipah viruses, and their grave threats to humans have begun a race in exploring the designing and developing of advanced vaccines, prophylactics, hera peutics, and drug regimens to counter emerging

 helicase activity. Among the evaluated compounds, 4-(cyclo-pent- 1-en-3-ylamino)-5-[2-(4- iodo-phenyl) hydra-zinyl]-4H-1,2,4-triazole-3-thiol and

4-(cyclopent-1-en-3-ylamino)-5-[2-(4- chlorophenyl)hydrazinyl]-4H-1,2,4-triazole-3-thiol were found to be the most potent. These compounds were used for in silico studies, and molecular docking was accomplished into the active binding site of MERS-CoV helicase nsp13 (21). Further studies are required for evaluating the therapeutic

potential of these newly identified compounds in the management of COVID-19 infection. Passive Immunization/Antibody Therapy/Mab Monoclonal antibodies (MAbs) may be helpful in

the intervention of disease in CoV-exposed individuals. Patients recovering from SARS showed robust neutralizing antibodies against this CoV infection (164). A set of MAbs aimed at the MERS- CoV S protein-specific domains, comprising six specific epitope groups interacting with receptor- binding, membrane fusion, and sialic acid-binding sites, make up crucial entry tasks of S protein (198, 199). Passive immunization employing weaker

·         strongly

·         antibodies

·         neutralizing

provided viruses in nasal washes, saliva, urine and faeces for up to 8 days after infection, and a few naive ferrets with only indirect contact were positive for viral RNA, suggesting airborne transmission. In addition, transmission of the virus through the ocular surface and prolonged presence of SARS-CoV-2 viral RNA in faecal samples were also documented 101,102. Coronaviruses can persist on inanimate surfaces for days, which could also be the case for SARS-CoV-2 and could pose a prolonged risk of infection ¹03. These findings explain the rapid geographic spread of COVID-19, and public health interventions to reduce transmission will provide benefit to mitigate the epidemic, as has proved successful in China and several other countries, such as South Korea 89,104,105. infections clinically or through routine lab tests. Therefore travel history becomes important. However, as the epidemic spreads, the travel history will become irrelevant. Treatment is essentially supportive and symptomatic.  Mild illness should be managed at home with counseling about danger signs. The usual principles are maintaining hydration and nutrition and controlling fever and cough. Routine use of antibiotics and antivirals such as oseltamivir should be avoided in confirmed cases. In hypoxic patients, provision of oxygen through nasal prongs, face mask, high flow nasal had >95% homology with the bat coronavirus and > 70% similarity with the SARS-CoV. Environmental samples from the Huanan sea food market also tested positive, signifying that the virus originated from there [7]. The number of cases started increasing exponentially, some of which did not have exposure to the live animal market, suggestive of the fact that human-to-human transmission was occurring [8]. The first fatal case was reported on 11th Jan 2020. The massive migration of Chinese during the Chinese New Year fuel led the epidemic. Cases in other provinces of China, other countries (Thailand, Japan and South Korea in quick succession) were reported in people who were returning from Wuhan. Transmission to healthcare workers caring for patients was described on 20th Jan, 2020. By 23rd January, the 11 million population of Wuhan identified angiotensin receptor 2 (ACE₂) as the receptor through which the virus enters the respiratory mucosa [11]. The basic case reproduction rate (BCR) is estimated to range from 2 to 6.47 in various modelling studies [11]. In comparison, the BCR of SARS was 2 and 1.3 for pandemic flu H1N1 2009 [2].

 

Clinical Features:

The clinical features of COVID-19 are varied, ranging from asymptomatic state to acute respiratory distress syndrome and multi organ dysfunction. The common clinical features include fever (not in all), cough, sore throat, headache, fatigue, headache, myalgia and breathlessness. Conjunctivitis has also been described. Thus, they are indistinguishable from other rocniratoru infections. In a cuhcot pandemic flu where patients were asked to resume work/school once afebrile for 24 h or by day 7 of illness. Negative molecular tests were not a prerequisite for discharge. At the community level, people should be asked to avoid crowded areas and postpone non-essential travel to places with ongoing transmission. They should be asked to practice cough hygiene by coughing in sleeve/ tissue rather than hands and practice hand hygiene frequently every 15-20 min. Patients with respiratory symptoms should be asked to use surgical masks. The use of mask by healthy people in public places has not shown to protect against respiratory viral infections and is currently not recommended by WHO. However, in China, the public has been asked to wear masks in public and especially in crowded places and large scale gatherings are prohibited (entertainment parks etc).

Immunomodulatory agents:

 

 SARS-CoV-2 triggers a strong immune response which may cause cytokine storm syndrome 60,61. Thus, immunomodulatory agents that inhibit the excessive inflammatory response may be a potential adjunctive therapy for COVID-19. Dexamethasone is a corticosteroid often used in a wide range of conditions to relieve inflammation through its anti-inflammatory and immunosuppressant effects. Recently, the RECOVERY trial found dexamethasone reduced mortality by about one third in hospitalized patients with COVID-19 who received invasive mechanical ventilation and by one fifth in patients receiving oxygen. By contrast, no benefit was found in patients without respiratory support¹ +-146 Tocilizumab and sarilumab, two types of interleukin-6 (IL-6) receptor-specific antibodies previously used to treat various types of arthritis, including rheumatoid arthritis, and cytokine release syndrome, showed effectiveness in the treatment of severe COVID-19 by attenuating the cytokine storm in a small uncontrolled trial¹47. Bevacizumab is an anti-vascular endothelial growth factor (VEGF) medication that could potentially reduce pulmonary oedema in patients with severe COVID-19. Eculizumab is a specific monoclonal antibody that inhibits the pro inflammatory complement protein C5 Preliminary results showed that it induced a drop of inflammatory markers and C-reactive protein levels, suggesting its potential to be an option for the treatment of severe COVID-19 (REF. 148). appeared asymptomatic". Another serological study detected SARS-CoV-2 neutralizing antibodies in cat serum samples collected in Wuhan after the COVID-19 outbreak, providing evidence for SARS-CoV-2 infection in cat populations in Wuhan, although the potential of SARS-CoV- transmission from cats to humans is currently uncertain.

 

 Receptor use and pathogenesis

SARS-CoV-2 uses the same receptor as SARS-CoV, angiotensin-converting enzyme 2 (ACE2)",. Besides human ACE2 (hACE2), SARS-CoV-2 also recognizes ACE2 from pig, ferret, rhesus monkey, civet, cat, pangolin, rabbit and dog'1.3.48.9, The broad receptor usage of SARS-CoV-2 implies that it may have a wide host range, and the varied efficiency of ACE2 usage in different animals may indicate their different susceptibilities to SARS-CoV-2 infection. The S1 subunit of corona- virus is further divided into two functional domains, an N-terminal domain and a C-terminal domain. Structural and biochemical analyses identified a 211 amino acid region (amino acids 319-529) at the S1 C-terminal domain of SARS-CoV-2 as the RBD, which has a key role in virus entry and is the target of neutralizing antibodies.

 

Breastfeeding and infant care

The data available to date is limited and cannot confirm whether or not COVID-19 can be transmitted through breast milk.40 Assessing the presence of COVID-19 in breast milk samples from six patients showed negative result.45 The CDC points out that in case of a confirmed or suspected COVID-19 infection, the decision of whether or how to start or continue breastfeeding should be made by the mother in collaboration with the family and healthcare practitioners.47 Careful precautions need to be taken by the mother to prevent transmitting the disease to her infant through respiratory droplets during breastfeeding. differs from that in SARS-CoV in the five residues critical for ACE2 binding, namely Y455L, L486F, N493Q, D494S and T501N52. Owing to these residue changes, interaction of SARS-CoV-2 with its receptor stabilizes the two virus-binding hotspots on the surface ofhACE2 (REF.5%) (FIG. 3d). Moreover, a four-residue motif in the RBM of SARS-CoV-2 (amino acids 482-485: G-V-E-G) results in a more compact conformation of its hACE2-binding ridge than in SARS-CoV and enables better contact with the N-terminal helix of hACE2 (REF.50). Biochemical data confirmed that the structural features of the SARS-CoV-2 RBD has strengthened its hACE2 binding affinity compared with that of

SARS-CoV 50,52,53 Similarly to other coronaviruses, SARS-CoV-2 needs proteolytic processing of the S protein to activate the endocytic route. It has been shown that host proteases participate in the cleavage of the S protein and activate the entry of SARS-CoV-2, including transmembrane protease serine protease 2 (TMPRSS2), cathepsin L and furin47,54,55. Single-cell RNA sequencing data showed that TMPRSS2 is highly expressed in several tissues and body sites and is co-expressed with ACE2 in nasal epithelial cells, lungs and bronchial branches, which explains some of the tissue tropism of SARS-CoV-2 (REFS 56,57). SARS-CoV-2 pseudovirus entry assays revealed that TMPRSS2 and cathepsin L have cumulative effects with furin on activating virus entry 55. Analysis of the cryoelectron microscopy structure of SARS-CoV-2 S protein revealed that its RBD is mostly in the lying-down state, whereas the SARS-CoV S protein assumes equally standing-up and lying-down conformational states 50,51,58,59. A lying-down conformation of theSARS-CoV-2 S protein may not be in favour of receptor binding but is helpful for immune evasion55. lower respiratory tracts. Acute viral interstitial pneumonia and humoral and cellular immune responses were observed 48,75. Moreover, prolonged virus shedding peaked early in the course of infection in asymptomatic macaques, and old monkeys showed severer interstitial pneumonia than young monkeys", which is similar to what is seen in patients with COVID-19. In human ACE2-transgenic mice infected with SARS-CoV-2, typical interstitial pneumonia was present, and viral anti- gens were observed mainly in the bronchial epithelial cells, macrophages and alveolar epithelia. Some human ACE2-transgenic mice even died after infection 70,71 In wide-type mice, a SARS-CoV-2 mouse-adapted strain with the N501Y alteration in the RBD of the S protein was generated at passage 6. Interstitial pneumonia and inflammatory responses were found in both young and aged mice after infection with the mouse-adapted strain74. Golden hamsters also showed typical symptoms after being infected with SARS-CoV-2 (REF.77). In other animal models, including cats and ferrets, SARS-CoV-2 could efficiently replicate in the upper respiratory tract but did not induce severe clinical symptoms43,78. As trans- mission by direct contact and air was observed in infected ferrets and hamsters, these animals could be used to model different transmission modes of COVID-19 (REFS77-79). Animal models offer important information for understanding the pathogenesis of SARS-CoV-2 infection and the transmission dynamics of SARS- CoV-2, and are important to evaluate the efficacy of antiviral therapeutics and vaccines.

 

Clinical and epidemiological features

It appears that all ages of the population are susceptible to SARS-CoV-2 infection, and the median age of infection is around 50 years 9,13,60,80,81. However, clinical manifestaions differ with age. In general, older men (>60 years old) with co-morbidities are more likely to develop severe respiratory disease that requires hospitalization vaccine, and li-Key peptide COVID-19 vaccine are under preclinical trials (297). Similarly, the WHO, on its official website, has mentioned a detailed list of COVID-19 vaccine agents that are under consideration. Different phases of trials are ongoing for live attenuated virus vaccines, formaldehyde alum inactivated vaccine, adenovirus type 5 vector vaccine, LNP-encapsulated mRNA vaccine, DNA plasmid vaccine, and S protein, S-trimer, and Ii-Key peptide as a subunit protein vaccine, among others (298). The process of vaccine development usually takes approximately ten years, in the case of inactivated or live attenuated vaccines, since it involves the generation of long-term efficacy data. However, this was brought down to 5 years during the Ebola emergency for viral vector vaccines. In the urgency associated with the COVID-19 outbreaks, we expect a vaccine by the end of this year (343). The development of an effective vaccine against COVID-19 with high speed and precision is the combined result of advancements in computational biology, gene synthesis, protein engineering, and the invention of advanced manufacturing platforms (342). The recurring nature of the coronavirus outbreaks calls for the development of a pan-coronavirus vaccine that can produce cross-reactive antibodies.

Immunoglobulin therapy:

 

 Convalescent plasma treatment is another potential adjunctive therapy for COVID-19. Preliminary findings have suggested improved clinical status after the treatment ¹53,154. The FDA has provided guidance for the use of COVID-19 convalescent plasma under an emergency investigational new drug application. However, this treatment may have adverse effects by causing antibody-mediated enhancement of infection, transfusion-associated acute lung injury and allergic transfusion reactions. Monoclonal antibody therapy is an effective immuno- therapy for the treatment of some viral infections in select patients. Recent studies reported specific monoclonal antibodies neutralizing SARS-CoV-2 infection minimum signs and symptoms (82). Another study, conducted in South Korea, related to SARS-CoV-2 viral load, opined that SARS-CoV-2 kinetics were significantly different from those of earlier reported CoV infections, including SARS-CoV (253). SARS- CoV-2 transmission can occur early in the viral infection phase; thus, diagnosing cases and isolation attempts for this virus warrant different strategies than those needed to counter SARS-CoV. Studies are required to establish any correlation between SARS- CoV-2 viral load and cultivable virus. Recognizing patients with fewer or no symptoms, along with having modest detectable viral RNA in the oropharynx for 5 days, indicates the requirement of data for assessing SARS-CoV-2 transmission dynamics and updating the screening procedures in the clinics (82). From experience with several outbreaks associated with known emerging viruses, higher pathogenicity of a virus is often associated with lower transmissibility. Compared to emerging viruses like Ebola virus, avian H7N9, SARS-CoV, and MERS-CoV, SARS-CoV-2 has relatively lower pathogenicity and moderate transmissibility (15). The risk of death among individuals infected with COVID-19 was calculated using the infection fatality risk (IFR). The IFR was found to be in the range of 0.3% to 0.6%, which is comparable to that of a previous Asian influenza pandemic (1957 to 1958) (73, 277).

Notably, the reanalysis of the COVID-19 pandemic curve from the initial cluster of cases pointed considerable human-to-human to transmission. It is opined that the exposure history of SARS CoV-2 at the Wuhan seafood market originated from human-to-human transmission rather than animal-to-human transmission (74); however, in light of the zoonotic spillover in COVID-19, is too early to fully endorse this idea (1). Following the initial infection, human-to-human transmission has been observed with a preliminary reproduction number (Ro) estimate of 1.4 to 2.5 (70, 75), and recently it is estimated to be 2.24 to 3.58 (76). In another study, the average reproductive number of Coronaviruses are a diverse group of viruses infecting many different animals, and they can cause mild to severe respiratory infections in humans. In 2002 and 2012, respectively, two highly pathogenic coronaviruses with zoonotic origin, severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), emerged in humans and caused fatal respiratory illness, making emerging coronaviruses a new public health concern in the twenty-first century¹. At the end of 2019, a novel coronavirus designated as SARS-CoV-2 emerged in the city of Wuhan, China, and caused an outbreak of unusual viral pneumonia. Being highly transmissible, this novel coronavirus disease, also known as coronavirus disease 2019 (COVID-19), has spread fast all over the world 2,3. It has overwhelmingly surpassed SARS and MERS in terms of both the number of infected people and the spatial range of epidemic areas. The ongoing outbreak of COVID-19 has posed an extraordinary threat to global public health 45. In this Review, we summarize the current understanding of the nature of SARS-CoV-2 and COVID-19. On the basis of recently published findings, this comprehensive Review covers the basic biology of SARS-CoV-2, including the genetic characteristics, the potential zoonotic origin and its receptor binding. Furthermore, we will discuss the clinical and epidemiological features, diagnosis of and countermeasures against COVID-19.

 

Emergence and spread:

In late December 2019, several health facilities in Wuhan, in Hubei province in China, reported clusters of patients with pneumonia of unknown cause. Similarly to patients with SARS and MERS, these patients showed symptoms of viral pneumonia, including fever, cough .The pathogenesis of SARS-CoV-2 infection in humans manifests itself as mild symptoms to severe respiratory failure. On binding to epithelial cells in the respiratory tract, SARS-CoV-2 starts replicating and migrating down to the airways and enters alveolar epithelial cells in the lungs. The rapid replication of SARS-CoV-2 in the lungs may trigger a strong immune response. Cytokine storm syndrome causes acute respiratory distress syndrome and respiratory failure, which is considered the main cause of death in patients with COVID-19 (REFS60,61). Patients of older age (>60 years) and with serious pre-existing diseases have a greater risk of developing acute respiratory distress syndrome and death 62-64 (FIG. 4). Multiple organ failure has also been reported in some COVID-19 cases9,13,65.

 Histopathological changes in patients with COVID-19 occur mainly in the lungs. Histopathology analyses showed bilateral diffused alveolar damage, hyaline membrane formation, desquamation of pneumocytes and fibrin deposits in lungs of patients with severe COVID-19. Exudative inflammation was also shown in some cases. Immunohistochemistry assays detected SARS-CoV-2 antigen in the upper airway, bronchiolar epithelium and submucosal gland epithelium, as well as in type I and type II pneumocytes, alveolar macrophages and hyaline membranes in the lungs 13,60,66,67 Animal models used for studying SARS-CoV-2 infection pathogenesis include non-human primates (rhesus macaques, cynomolgus monkeys, marmosets and African green monkeys), mice (wild-type mice (with mouse-adapted virus) and human ACE2-transgenic or human ACE2-knock-in mice), ferrets and golden hamsters 43,48,68-74. In non-human primate animal models, most species display clinical features similar to those of patients with COVID-19, including virus shedding, virus replication and host responses to SARS-CoV-2 infection 69,72,73. For example, in the rhesus macaque model, high viral loads were detected in the upper and countries have a fragile health system that can be crippled in the event of an outbreak. Effective management of COVID-19 would be difficult for low-income countries due to their inability to respond rapidly due to the lack of an efficient health care system (65). Controlling the imported cases is critical in preventing the spread of COVID-19 to other countries that have not reported the disease until now. The possibility of an imported case of COVID-19 leading to sustained human-to-human transmission was estimated to be 0.41. This can be reduced to a value of 0.012 by decreasing the mean time from the onset of symptoms to hospitalization and can only be made possible by using intense disease surveillance systems (235). The silent importations of infected individuals (before the manifestation of clinical signs) also contributed significantly to the spread of disease across the major cities of the world. Even though the travel ban was implemented in Wuhan (89), infected persons who traveled out of the city just before the imposition of the ban might have remained undetected and resulted in local outbreaks (236). Emerging novel diseases like COVID-19 are difficult to contain within the country of origin, since globalization has led to a world without borders. Hence, international collaboration plays a vital role Currently, our knowledge on the animal origin of SARS-CoV-2 remains incomplete to a large part. The reservoir hosts of the virus have not been clearly proven. It is unknown whether SARS-CoV-2 was transmitted to humans through an intermediate host and which animals may act as its intermediate host. Detection of RaTG13, RmYN02 and pangolin coronaviruses implies that diverse coronaviruses similar to SARS-CoV-2 are circulating in wildlife. In addition, as previous studies showed recombination as the potential origin of some sarbecoviruses such as SARS CoV, it cannot be excluded that viral RNA recombination among different related coronaviruses was involved in the evolution of SARS-CoV-2. Extensive surveillance of SARS-CoV-2- related viruses in China, Southeast Asia and other regions targeting bats, wild and captured pangolins and other wildlife species will help us to better understand the zoonotic origin of SARS-CoV-2. Besides wildlife, researchers investigated the susceptibility of domesticated and laboratory animals to SARS-CoV-2 infection. The study demonstrated experimentally that SARS-CoV-2 replicates efficiently in cats and in the upper respiratory tract of ferrets, whereas dogs, pigs, chickens and ducks were not susceptible to SARS-CoV-2 (REF. 43). The susceptibility of minks was documented by a report from the Netherlands on an outbreak of SARS-CoV-2 infection in farmed minks. Although the symptoms in most infected minks were mild, some developed severe respiratory distress and died of interstitial pneumonia44. Both virological and serological testing found evidence for natural SARS-CoV-2 infection in two dogs from households with human cases of COVID-19 in Hong Kong, but the dogs encircled with an envelope containing viral nucleocapsid. The nucleocapsids in CoVs are in helical symmetry, which reflects an atypical attribute in positive-sense RNA viruses (30). The electron micrographs of SARS-CoV-2 revealed a diverging spherical outline with some degree of pleomorphism, virion diameters varying from 60 to 140 nm, and distinct spikes of 9 to 12 nm, giving the virus the appearance of a solar corona (3). The CoV genome is arranged linearly as 5'-leader-UTR- replicase-structural genes genes (S-E-M-N)-3′ UTR- poly(A) (32). Accessory genes, such as 3a/b, 4a/b, and the hemagglutinin-esterase gene (HE), are also seen intermingled with the structural genes (30). SARS-CoV-2 has also been found to be arranged similarly and encodes several accessory proteins, although it lacks the HE, which is characteristic of some beta coronaviruses (31). The positive-sense genome of CoVs serves as the mRNA and is translated to polyprotein la/lab (ppla/lab) (33). A replication-transcription complex (RTC) is formed in membrane vesicles (DMVs) by nonstructural proteins (nsps), encoded by the polyprotein gene (34). Subsequently, the RTC synthesizes a nested set of sub-genomic RNAs (sg RNAs) via discontinuous transcription (35).

 

THE VIRUS (SARS-CoV-2):

Coronaviruses are positive-sense RNA viruses having an extensive and promiscuous range of natural hosts and affect multiple systems (23, 24). Coronaviruses can cause clinical diseases in humans that may extend from the common cold to more severe respiratory diseases like SARS and MERS (17, 279). The recently emerging SARS-CoV-2 has wrought havoc in China and caused a pandemic situation in the worldwide population leading to considerable protection in mice against a MERS- CoV lethal challenge. Such antibodies may play a crucial role in enhancing protective humoral responses against the emerging CoVs by aiming appropriate epitopes and functions of the S protein. The cross-neutralization ability of SARS-CoV RBD- specific neutralizing MAbs considerably relies on the resemblance between their RBDs; therefore, SARS-CoV RBD-specific antibodies could cross- neutralized SL CoVs, i.e., bat-SL-CoV strain WIV1 (RBD with eight amino acid differences from SARS- CoV) but not bat-SL-CoV strain SHC014 (24 amino acid differences) (200). Appropriate RBD-specific MAbs can be recognized by a relative analysis of RBD of SARS- CoV-2 to that of SARS-CoV, and cross-neutralizing SARS-CoV RBD-specific MAbs could be explored for their effectiveness against COVID-19 and further need to be assessed clinically. The U.S. biotechnology company Regeneron is attempting to recognize potent and specific MAbs to combat COVID-19. An ideal therapeutic option suggested or SARS-CoV-2 (COVID-19) is the combination therapy .comprised of MAbs and the drug remdesivir (COVID-19) (201). The SARS-CoV-specific human MAb CR3022 is found to bind with SARS-CoV-2 RBD, indicating its potential as a therapeutic agent species barrier. A recent, suffering from novel SARS-CoV-2, with more than 4,170,424 cases and 287,399 deaths across the globe. There is an urgent need for a rational international campaign against the unhealthy food practices of China to encourage the sellers to increase hygienic food practices or close the crude live-dead animal wet markets. There is a need to modify food policies at national and international levels to avoid further life threats and economic consequences from any emerging or reemerging pandemic due to close animal-human interaction (285).

 World Even though individuals of all ages and sexes are susceptible to COVID-19, older people with an underlying chronic disease are more likely to become severely infected (80). Recently, individuals with asymptomatic infection were also found to act as a source of infection to susceptible individuals (81). Both the asymptomatic and symptomatic patients secrete similar viral loads, which indicates that the transmission capacity of asymptomatic or minimally symptomatic patients is very high. Thus, SARS-CoV-2 transmission can happen early in the course of infection (82). Atypical clinical manifestations have also been reported in COVID-19 in which the only reporting symptom was fatigue. Such patients may lack respiratory signs, such as fever, cough, and sputum (83). Hence, the clinicians RBD, indicating its potential as a therapeutic agent in the management of COVID-19. It can be used alone or in combination with other effective neutralizing antibodies for the treatment and prevention of COVID-19 (202). Furthermore, SARS-CoV-specific neutralizing antibodies, like m396 and CR3014, failed to bind the S protein of SARS-CoV- 2, indicating that a particular level of similarity is mandatory between the RBDs of SARS-CoV and SARS-CoV-2 for the cross-reactivity to occur. Further assessment is necessary before confirming the effectiveness of such combination therapy. In addition, to prevent further community and nosocomial spread of spread of COVID-19, the post procedure risk management program should not be neglected (309). Development of broad-spectrum inhibitors against the human coronaviral pathogens will help to facilitate clinical trials on the effectiveness of such inhibitors against endemic and emerging coronaviruses (203). A promising animal study revealed the protective effect of passive immunotherapy with immune serum from MERS- immune camels on mice infected with MERS-CoV (204). Passive immunotherapy using convalescent is another strategy that can be used for treating COVID-19-infected, critically ill patients (205).

 Serological testing

 

Serological surveys are also considered to be one of the most effective ones in facilitating outbreak investigation and it also helps us to derive a retrospective assessment of the disease by estimating the attack rate.32 According to the recent literature, paired serum samples can also help clinicians to diagnose COVID-19 in case of false negative results in NAAT essays.37 The literature also declared that the commercial and non-commercial serological tests are under consideration in order to support the practicing clinicians by assisting them in diagnosis. Similarly, there are studies published on COVID-19 which are comprised of the serological data on clinical samples.

 

Viral sequencing

Apart from confirming the presence of virus in the specimens, viral sequencing is also quite useful in monitoring the viral genomic mutations, which plays a very significant role in influencing the performance of the medical countermeasures inclusive of the diagnostic test. Genomic sequencing of the virus can also help further in developing several studies related to molecular epidemiology.32 as an entry receptor while exhibiting an RBD similar to that of SARS-CoV (17, 87, 254, 255). Several countries have provided recommendations to their people traveling to China (88, 89). Compared to the previous coronavirus outbreaks caused by SARS- CoV and MERS-CoV, the efficiency of SARS-CoV- 2 human-to-human transmission was thought to be less. This assumption was based on the finding that health workers were affected less than they were in previous outbreaks of fatal coronaviruses (2). Super spreading events are considered the main culprit for the extensive transmission of SARS and MERS (90, 91). Almost half of the MERS-CoV cases reported in Saudi Arabia are of secondary origin that occurred through contact with infected asymptomatic or symptomatic individuals through human-to-human transmission (92). The occurrence of super spreading events in the COVID-19 outbreak cannot be ruled out until its possibility is evaluated. Like SARS and MERS, COVID-19 can also infect the lower respiratory tract, with milder symptoms (27). The basic reproduction number of COVID-19 has been found to be in the range of 2.8 to 3.3 based on real-time reports and 3.2 to 3.9 based on predicted infected cases (84).

Mode of transmission

Infact it was accepted that the original transmission originated from a seafood market, which had a tradition of selling live animals, where the majority of the patients had either worked or visited, although up to now the understanding of the COVID-19 transmission risk remains incomplete. 16 In addition, while the newer patients had no exposure to the market and still got the virus from the humans present there, there is an increase in the outbreak.

 

Viral replication

Usually replication of coronavirus occurs within the cytoplasm and is closely associated with endoplasmic reticulum and other cellular membrane organelles. Human coronaviruses are thought to invade cells, primarily through different receptors. For 229E and OC43, amino peptidase-N (AP-N) and a sialic acid containing receptor, respectively, were known to function in this role. After the virus enters the host cell and un coating process occurs, the genome is transcribed, and then, translated. A characteristic feature of replication is that all mRNAs form an enclosed group of typical 3' ends; only the special portions of the 5' ends are translated. In total, about 7 mRNAs are produced. The shortest mRNA codes and the others can express the synthesis of another genome segment for nucleoprotein. At the cell membrane, these proteins are collected and genomic RNA is initiated as a mature particle type by burgeoning from internal cell membranes.

 

PATHOGENESIS

Coronaviruses are tremendously precise and mature in most of the airway epithelial cells as observed through both in vivo and in vitro COVID-19 patients showing severe signs are treated symptomatically along with oxygen therapy. In such cases where the patients progress toward respiratory failure and become refractory to oxygen therapy, mechanical ventilation is necessitated. The COVID-19-induced septic shock can be managed by providing adequate hemodynamic support (299). Several classes of drugs are currently being evaluated for their potential therapeutic action against SARS-CoV-2. Therapeutic agents that have anti-SARS-CoV-2 activity can be broadly classified into three categories: drugs that block virus entry into the host cell, drugs that block viral replication as well as its survival within the host cell, and drugs that attenuate the exaggerated host immune response (300). An inflammatory cytokine storm is commonly seen in critically ill COVID-19 patients. Hence, they may benefit from the use of timely anti-inflammation treatment. Anti-inflammatory therapy using drugs like glucocorticoids, cytokine inhibitors, JAK inhibitors, and chloroquine/hydroxyl chloroquine should be done only after analyzing the risk/benefit ratio in COVID-19 patients (301). There have not been any studies concerning the application of nonsteroidal anti-inflammatory drugs (NSAID) to COVID-19-infected patients. However, reasonable pieces of evidence are available that link NSAID.

PREGNANCY

 

Currently, there is a paucity of knowledge and data related to the consequences of COVID-19 40-42 during pregnancy. However, pregnant women seem to have a high risk of developing severe infection and complications during the recent 2019-nCoV outbreak.41-43 This speculation was based on previous available scientific reports on coronaviruses during pregnancy (SARS-CoV and MERS-CoV) as well as the limited number of COVID-19 cases.Analysing the clinical features and outcomes of 10 newborns (including two sets of twins) in China, whose mothers are confirmed cases of COVID-19, revealed that perinatal infection with 2019-nCoV may lead to adverse outcomes for the neonates, for example, premature labour, respiratory distress, thrombocytopenia with abnormal liver function and even death.44 It is still unclear whether or not the COVID-19 infection can be transmitted during pregnancy to the foetus through the transplacental route. 42 A recent case series report, which assessed intrauterine vertical transmission of wearing a facemask and practicing hand hygiene before feeding the baby. In addition, it is advisable that breast pumps are cleaned. properly after each use and, if possible, a healthy individual is available to feed the expressed breast milk to the infant.

 

 Children and elderly population

On the basis of the available reports, COVID-19 among children accounted for 1-5% of the confirmed cases, and this population does not seem to be at higher risk for the disease than adults. There is no difference in the COVID-19 symptoms between adults and children. However, the available evidence indicated that children diagnosed with COVID-19 have milder symptoms than the adults, with a low mortality rate. 48, 49 On the contrary, older people who are above the age of 65 years are at higher risk for a severe course of disease. In the United Stated, approximately 31-59% of those with confirmed COVID-19 between the ages of 65 and 84 years old required hospitalization, 11-31% of them. required admission to the intensive care unit, and 4-11% died.

Infection & diseases

Respiratory infection (SARI) and respiratory distress, shock or hypoxaemia. Patients with SARI can be given conservative fluid therapy only when there is no evidence of shock. Empiric antimicrobial therapy must be started to manage SARI. For patients with sepsis, antimicrobials must be administered within 1 hour of initial assessments. The WHO and CDC recommend that glucocorticoids not be used in patients with COVID-19 pneumonia except where there are other indications (exacerbation of chronic obstructive pulmonary disease).5⁹ Patients' clinical deterioration is closely observed with SARI; however, rapidly progressive respiratory failure and sepsis require immediate supportive care interventions comprising quick use of neuromuscular blockade and sedatives, hemodynamic management, nutritional support, maintenance of blood glucose levels, prompt assessment and treatment of nosocomial pneumonia, and prophylaxis against deep venous thrombosis (DVT) and gastrointestinal (Gl) bleeding.60 Generally, such patients give way to their primary illness to secondary complications like sepsis or multi organ system failure.48 Recently, 95 full-length genomic sequences of SARAS-CoV-2 strains available in the National Center for Biotechnology Information and GISAID databases were subjected to multiple-sequence alignment and phylogenetic analyses for studying variations in the viral genome (260). All the viral strains revealed high homology of 99.99% (99.91% to 100%) at the nucleotide level and 99.99% (99.79% to 100%) at the amino acid level. Overall variation was found to be low in ORF regions, with 13 variation sites recognized in 1a, 1b, S, 3a, M, 8, and N regions. Mutation rates of 30.53% (29/95) and 29.47% (28/95) were observed at nt 28144 (ORF8) and nt 8782 (ORF1a) positions, respectively. Owing to such selective mutations, a few specific regions of SARS-CoV-2 should not be considered for designing primers and probes. The SARS-CoV-2 reference sequence could pave the way to study molecular biology and pathobiology, along with developing diagnostics and appropriate prevention and control strategies for countering SARS-CoV-2 (260). Nucleic acids of SARS-CoV-2 can be detected from samples (64) such as bronchoalveolar lavage fluid, sputum, nasal swabs, fiber bronchoscope brush biopsy specimen, pharyngeal swabs, feces, blood, and urine, with different levels of diagnostic performance (Table 2) (80, 245, 246). Heptad repeat 1 (HR1) and heptad repeat 2 (HR2) can interact and form a six-helix bundle that brings the viral and cellular membranes in close proximity, facilitating its fusion. The sequence alignment study conducted between COVID-19 and SARS-CoV identified that the S2 subunits are highly conserved in these CoVs. The HR1 and HR2 domains showed 92.6% and 100% overall identity, respectively (210). From these findings, we can confirm the significance of COVID-19 HR1 and HR2 and their vital role in host cell entry. Hence, fusion inhibitors target the HR1 domain of S protein, thereby preventing viral fusion and entry into the host cell. This is another potential therapeutic strategy that can be used in the management of COVID-19. Other than the specific therapy directed against COVID-19, general treatments play a vital role in the enhancement of host immune responses against the viral agent. Inadequate nutrition is linked to the weakening of the host immune response, making the individual more susceptible. The role played by nutrition in disease susceptibility should be measured by evaluating the nutritional status of patients with COVID-19 (205).

ANTIVIRAL THERAPY

 

COVID-19 is an infectious disease caused by SARS-CoV-2, which is also termed the novel

coronavirus and is diligently associated with the SARS virus. The Ministry of Science and Technology from the People's Republic of China declared three potential antiviral medicines suitable for treating COVID-19. Those three medicines are, namely, Favilavir, chloroquine phosphate and remdesivir. A clinical trial was conducted to test the efficacy of those three drugs, and the results proved that out of the three medicines above only Favilavir is effective in treating the patients with novel coronavirus. The remaining two drugs were effective in treating malaria.62 Likewise a study carried out in the United States by the National Institute of Health proved that remdesivir is effective in treating the Middle East respiratory syndrome coronavirus (MERS- CoV), which is also a type of coronavirus that was transmitted from monkeys. The drug remdesivir was also used in the United States for treating the patients with COVID-19. There has been a proposal to use the combination of protease inhibitors lopinavir-ritonavir for treating the patients affected by COVID-19.62. results of the clinical trial showed that the patients who were given chloroquine had a significant reduction in their body temperature. The clinical trial also showed better recovery among the patients who were given chloroquine and hydroxy chloroquine.63 Hydroxyl chloroquine treatment is significantly associated with viral load reduction as well as disappearance in COVID-19 patients. Further, the outcome is reinforced by azithromycin. The role of lopinavir and ritonavir in the treatment of COVID-19 is uncertain. A potential benefit was suggested by preclinical data, but additional data has failed to confirm it. Tocilizumab is an immune-modulating agent used as adjunct therapy in some protocols based on a theoretical mechanism and limited preliminary data.

HOME CARE

 

Home management may be appropriate for patients with mild infection who can be adequately isolated in the outpatient setting. Management of such patients should focus on prevention of transmission to others, and monitoring for clinical deterioration, which should prompt hospitalization. Interim recommendations on home management of patients with COVID-19 can be found.

Measures

• Ø  All clinicians should keep

        themselves updated about recent

        developments including global

        spread of the disease.

 

• Ø  Non-essential international travel

        should be avoided at this time.

 

• Ø  People should stop spreading.

        myths and false information about

        the disease and try to allay panic.

        and anxiety of the public.

Abstract

There is a new public health crises threatening the world with the emergence and spread of 2019 novel coronavirus (2019-nCoV) or the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus originated in bats and was transmitted to humans through yet unknown intermediary animals in Wuhan, Hubei province, China in December 2019. There have been around 96,000 reported cases of coronavirus disease 2019 (COVID-2019) and 3300 reported deaths to date (05/03/2020). The disease is transmitted by inhalation or contact with infected droplets and the incubation period ranges from 2 to 14 d. The symptoms are usually fever, cough, sore throat, breathlessness, fatigue, malaise among others.

Future perspectives:

 

COVID-19 is the third highly pathogenic human coronavirus disease to date. Although less deadly than SARS and MERS, the rapid spreading of this highly contagious disease has posed the severest threat to global health in this century. The SARS-CoV-2 outbreak has lasted for more than half a year now, and it is likely that Even though a high similarity has been reported between the genome sequence of the new coronavirus (SARS-CoV-2) and SARS-like CoVs, the comparative analysis recognized a furin-like cleavage site in the SARS-CoV-2 S protein that is missing from other SARS-like CoVs (99). The furin- like cleavage site is expected to play a role in the life cycle of the virus and disease pathogenicity and might even act as a therapeutic target for furin inhibitors. The highly contagious nature of SARS- CoV-2 compared to that of its predecessors might be the result of a stabilizing mutation that occurred in the endosome-associated-protein-like domain of nsp2 protein. Similarly, the destabilizing mutation near the phosphatase domain of nsp3 proteins in SARS-CoV- 2 could indicate a potential mechanism that differentiates it from other CoVs (100). Even though the CFR reported for COVID-19 is meager compared to those of the previous SARS and MERS outbreaks, it has caused more deaths than SARS and MERS combined (101). Possibly related to the viral pathogenesis is the recent finding of an 832- nucleotide (nt) deletion in ORF8, which appears to reduce the replicative fitness of the virus and leads to attenuated phenotypes of SARS-CoV-2 (256). Coronavirus is the most prominent example of a challenge with MERS-CoV (169). The intranasal administration of the recombinant adenovirus-based vaccine in BALB/c mice was found to induce long-lasting neutralizing immunity against MERS spike pseudo typed virus, characterized by the induction of systemic IgG, secretory IgA, and lung-resident memory T-cell responses (177). Immuno-informatics methods have been employed for the genome-wide screening of potential vaccine targets among the different immunogens of MERS-CoV (178). The N protein and the potential B-cell epitopes of MERS- COV E protein have been suggested as immune-protective targets inducing both T-cell and neutralizing antibody responses (178, 179). The collaborative effort of the researchers of Rocky Mountain Laboratories and Oxford University is designing a chimpanzee adenovirus-vectored vaccine to counter COVID-19 (180). The Coalition for Epidemic Preparedness Innovations (CEPI) has initiated three programs to design SARS-CoV-2 vaccines (181). CEPI has a collaborative project with Inovio for designing a MERS-CoV DNA vaccine that could potentiate effective immunity. CEPI and the University of Queensland are designing a molecular clamp vaccine platform for MERS-CoV and other pathogens, which could assist in the easier identification of antigens by the immune system (181). CEPI has also funded Modern to develop a explored targeting molecular dynamic simulations, evaluating their interaction with corresponding major histocompatibility complex class I molecules. They potentially induce immune responses (176). The recombinant vaccine can be designed by using rabies virus (RV) as a viral vector. RV can be made to express MERS-CoV S1 protein on its surface so that an immune response is induced against MERS-CoV. The RV vector-based vaccines against MERS-CoV can induce faster antibody response as well as higher degrees of cellular immunity than the Gram-positive enhancer matrix (GEM) particle vector-based vaccine. However, the latter can induce a very high antibody response at lower doses (167). Hence, the degree of humoral and cellular immune responses produced by such vaccines depends upon the vector used. Dual vaccines have been getting more popular recently. Among them, the rabies virus-based vectored vaccine platform is used to develop vaccines against emerging infectious diseases. The dual vaccine developed from inactivated rabies virus particles that express the MERS-CoV S1 domain of S protein was found to induce immune responses for both MERS-CoV and rabies virus. The vaccinated mice were found to be completely protected from challenge with MERS-CoV (169). The intranasal Based on molecular characterization, SARS- CoV-2 is considered a new Betacoronavirus belonging to the subgenus Sarbecovirus (3). A few other critical zoonotic viruses (MERS-related CoV and SARS-related CoV) belong to the same genus. However, SARS-CoV-2 was identified as a distinct virus based on the percent identity with other Betacoronavirus;   conserved open reading frame 1a/b (ORF1a/b) is below 90% identity (3). An overall 80% nucleotide identity was observed between SARS-CoV-2 and the original SARS-CoV, along with 89% identity with ZC45 and ZXC21 SARS- related CoVs of bats (2, 31, 36). In addition, 82% identity has been observed between SARS-CoV-2 and human SARS-CoV Tor2 and human SARS-CoV BJ01 2003 (31). A sequence identity of only 51.8% was observed between MERS-related CoV and the recently emerged SARS-CoV-2 (37). Phylogenetic analysis of the structural genes also revealed that SARS-CoV-2 is closer to bat SARS-related COV. Therefore, SARS-CoV-2 might have originated from bats, while other amplifier hosts might have played a role in disease transmission to humans (31). Of note, the other two zoonotic CoVs (MERS-related CoV and SARS-related CoV) also originated from bats (38, 39). Nevertheless, for SARS and MERS, civet The exploration of fully human antibodies (human single-chain antibodies; HuscFvs) or humanized nanobodies (single-domain antibodies; sdAb, VH/VHH) could aid in blocking virus replication, as these agents can traverse the virus- infected cell membranes (transbodies) and can interfere with the biological characteristics of the replicating virus proteins. Such examples include transbodies to the influenza virus, hepatitis C virus, Ebola virus, and dengue virus (206). Producing similar transbodies against intracellular proteins of coronaviruses, such as papain-like proteases (PLpro), cysteine-like protease (3CLpro), or other nsps, which are essential for replication and transcription of the virus, might formulate a practical move forward for a safer and potent passive immunization approach for virus-exposed persons and rendering therapy to infected patients. In a case study on five grimly sick patients having symptoms of severe pneumonia due to COVID-19, convalescent plasma administration was found to be helpful in patients recovering successfully. The convalescent plasma containing a SARS-CoV-2-specific ELISA (serum) antibody titer higher than 1:1,000 and neutralizing antibody titer more significant than 40 was collected from the recovered patients and used for plasma transfusion.

CONCLUSION

Several years after the global SARS epidemic, the current SARS-CoV-2/COVID-19 pandemic has served as a reminder of how novel pathogens can rapidly emerge and spread through the human population and eventually cause severe public health crises. Further research should be conducted to establish animal models for SARS-CoV-2 to investigate replication, transmission dynamics, and pathogenesis in humans. This may help develop and evaluate potential therapeutic strategies against zoonotic CoV epidemics. Present trends suggest the occurrence of future outbreaks of CoVs due to changes in the climate, and ecological conditions may be associated with human-animal contact. Live- animal markets, such as the Huanan South China Seafood Market, represent ideal conditions for interspecies contact of wildlife with domestic birds, pigs, and mammals, which substantially increases the probability of interspecies transmission of CoV infections and could result in high risks to humans due to adaptive genetic recombination in these viruses (323-325). The COVID-19-associated symptoms are fever, cough, expectoration, headache, and myalgia or fatigue. Individuals with asymptomatic and atypical patients with COVID-19 can be found on the WHO and CDC websites. The corona virus (COVID-19) spreads at an alarming rate all over the world. The outbreak of the virus has confronted the world's economic, medical and public health infrastructure. Elderly and immunocompromised patients also are susceptible to the virus's mortal impacts. Currently, there is no documented cure for the virus and no vaccine has been created, although some treatment protocols have been promising. Therefore, the virus can be controlled with the appropriate prevention strategies. Also, attempts have to be made to formulate systematic strategies to prevent such future zoonotic outbreaks. This new virus outbreak has challenged the economic, medical and public health infrastructure of China and to some extent, of other countries especially, its neigh bours. Time alone will tell how the virus will impact our lives here in India. More so, future outbreaks of viruses and pathogens of zoonotic origin are likely to continue. Therefore, apart from curbing this outbreak.

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