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observed through both in vivo and in vitro experiments. There is an enhanced nasal secretion observed along with
local oedema because of the damage of the host cell, which further stimulates the synthesis of inflammatory
mediators. In addition, these reactions can induce sneezing, difficulty breathing by causing airway inhibition and
elevate mucosal temperature. These viruses, when released, chiefly affect the lower respiratory tract, with the signs
and symptoms existing clinically. Also, the virus further affects the intestinal lymphocytes, renal cells, liver cells
and T-lymphocytes. Furthermore, the virus induces T-cell apoptosis, causing the reaction of the T-cell to be erratic,
resulting in the immune system's complete collapse.24, 25

5.1 Mode of transmission

In fact 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 of

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susceptible individuals. Hence, hand hygiene is equally as important as the use of appropriate PPE, like face masks,
to break the transmission cycle of the virus; both hand hygiene and face masks help to lessen the risk of COVID-19
transmission (315). Medical staff are in the group of individuals most at risk of getting COVID-19 infection. This is
because they are exposed directly to infected patients. Hence, proper training must be given to all hospital staff on
methods of prevention and protection so that they become competent enough to protect themselves and others from
this deadly disease (316). As a preventive measure, health care workers caring for infected patients should take
extreme precautions against both contact and airborne transmission. They should use PPE such as face masks (N9S
or FFP3), eye protection (goggles) gowns, and gloves to nullify the risk of infection (299). The human-to-human
transmission reported in SARS-CoV-2 infection occurs mainly through droplet or direct contact. Due to this finding,
frontline health care workers should follow stringent infection control and preventive measures, such as the use of
PPE, to prevent infection (110). The mental health of the medical/health workers who are involved in the COVID-19
outbreak is of great

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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%,
noninvasive ventilation in 13%, mechanical ventilation in 4%, extracorporeal membrane oxygenation CECMO) 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
[median 9 d]

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wrought havoc China and caused pandemic situation in the worldwide population, leading to discase outbreaks that
have not been controlled to date, although extensive efforts are being put in place to counter this virus (25). This
virus has been proposed to be designated/named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by
the International Committee on Taxonomy of Viruses (ICTV), which determined the virus belongs to the Severe
acute respiratory syndrome-related coronavirus category and found this virus is related to SARS-CoVs (26). SARS-
CoV-2 is a member of the order Nidovirales, family Coronaviridae, subfamily Orthocoronavirinae, which is
subdivided into four genera, viz., Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus (3,
27). The Benera Alphacoronavirus and Betacoronavirus originate from bats, while Gammacorona virus and
Deltacoronavirus have evolved from bird and swine gene pools (24, 28, 29, 275).

Coronaviruses possess an unsegmented, single stranded, positive-sense RNA genome of around 30 kb, enclosed by a
5'-cap and 3-poly(A) tail (30). The genome of SARS-CoV-2 is 29,89 1 bp long, with a G+C content of 38% (31).
These viruses are encircled with an envelope containing viral

Image 55

4.2 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 uncoating 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.22, 23

5 PATHOGENESIS
Coronaviruses are tremendously precise and mature in most of the airway epithelial cells as observed through both
in vivo and in vitro

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between 4 and -70°C. Urine samples must also be collected using a sterile container and stored in the laboratory at a
temperature that ranges between 4 and -70°C.32

7 PREGNANCY

Currently, there is a paucity of knowledge and data related to the consequences of COVID-19 during pregnancy. 40-42
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. 41-43 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

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8 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 handwash 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
meter 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 sterilise 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 minimise the risk of exposure to COVID-19 during outbreaks.53

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6.5 Specimen Collection and storage

A nasopharyngeal and oropharyngeal swab should be collected using Dacron or polyester flocked swabs. It should
be transported to the laboratory at a temperature of 4°C and stored in the laboratory between 4 and -70°C on the
basis of the number of days and, in order to increase the viral load, both nasopharyngeal and oropharyngeal swabs
should be placed in the same tube. Bronchoalveolar lavage and nasopharyngeal aspirate should be collected in a
sterile container and transported similarly to the laboratory by maintain a temperature of 4°C. Sputum samples,
especially from the lower respiratory tract, should be collected with the help of a sterile container and stored,
whereas tissue from a biopsy or autopsy should be collected using a sterile container along with saline. However,
both should be stored in the laboratory at a temperature that ranges between 4 and -70°C. Whole blood for detecting
the antigen, particularly in the first week of illness, should be collected in a collecting tube and stored in the
laboratory between 4 and-70°C. Urine samples must also be collected using a sterile container and stored

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differs from that in SARS-CoV in the five residues critical for ACE2 binding, namely Y455L, L486Ę, N493Q.
D494S and T501N52 (FIG. 3b,c). Owing to these residue changes, interaction of SARS-CoV-2 with its receptor
stabilizes the two virus-binding hotspots on the surface ofhACE2 (REF.50) (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-CoV50,52,53 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
TMPRS$2 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 TMPRS$2 and cathepsin L have cumulative effects with furin on
activating virus entry55. Analysis of the cryo-electron 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 states50,51`,58,59. A lying-down conformation of the SARS-CoV-2 S protein may not be in favour
of receptor binding but is helpful for immune evasion55.

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turtles, ducks, fish, Siamese crocodiles, and other animal meats without any fear of COVID-19. The Chinese
government is encouraging people to feel they can return to normalcy. However, this could be a risk, as it has been
mentioned in advisories that people should avoid contact with live-dead animals as much as possible, as SARS-
CoV-2 has shown zoonotic spillover. Additionally, we cannot rule out the possibility of new mutations in the same
virus being closely related to contact with both animals and humans at the market (284). In January 2020, China
imposed a temporary ban on the sale of live dead animals in wet markets. However, now hundreds of such wet
markets have been reopened without optimizing standard food safety and sanitation practices (286). With China
being the most populated country in the world and due to its domestic and international food exportation policies,
the whole world is now facing the menace of COVID-19, including China itself. Wet markets of live-dead animals
do not maintain strict food hygienic practices. Fresh blood splashes are present everywhere, on the floor and
tabletops, and such food customs could encourage many pathogens to adapt, mutate, and jump the species barrier.
As a result, the whole world is suffering from novel SARS-CoV-2, with more than
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Significance of frequent and good hand hygiene and sanitation practices needs to be given due emphasis (249-252).
Future explorative research needs to be conducted with regard to the fecal-oral transmission of SARS-CoV-2, along
with focusing on environmental investigations to find out if this virus could stay viable in situations and
atmospheres facilitating such potent routes of transmission. The correlation of fecal concentrations of viral RNA
with disease severity needs to be determined, along with assessing the gastrointestinal symptoms and the possibility
of fecal SARS-CoV-2 RNA detection during the coVID-19 incubation period or convalescence phases of the disease
(249-252). The lower respiratory tract sampling techniques, like bronchoalveolar lavage fluid aspirate, are
considered the ideal clinical materials, rather than the throat swab, due to their higher positive rate on the nucleic
acid test (148). The diagnosis of COVID19 can be made by using upper-respiratory-tract specimens collected using
nasopharyngeal and oropharyngeal swabs. However, these techniques are associated with unnecessary risks to health
care workers due to close contact with patients (152). Similarly, a single patient with a high viral load was reported
to contaminate an entire endoscopy room by shedding the virus, which may remain viable for at

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considerable proiccii01n 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 for 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

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visible signs of infection, making it challenging to identify animals actively excreting MERS-CoV that has the
potential to infect humans. However, they may shed MERS-CoV through milk, urine, feces, and nasal and eye
discharge and can also be found in the raw organs (108). In a study conducted to evaluate the susceptibility of
animal species to MERS-CoV infection, Ilamas and pigs were found to be susceptible, indicating the possibility of
MERS-CoV circulation in animal species other than dromedary camels (109).

Following the outbreak of SARS in China, SARS-CoV-like viruses were isolated from Himalayan palm civets
(Paguma larvata) and raccoon dogs (Nyctereutes procyonoides) found in a live-animal market in Guangdong,
China. The animal isolates obtained from the live-animal market retained a 29-nucleotide sequence that was not
present in most of the human isolates (78). These findings were critical in identifying the possibility of interspecies
transmission in SARS-CoV. The higher diversity and prevalence of bat coronaviruses in this region compared to
those in previous reports indicate a host/pathogen coevolution. SARS-like coronaviruses also have been found
circulating in the Chinese horseshoe bat (Rhinolophus sinicus) populations. The in vitro and in vivo studies carried

Image 64

mask and practice cough hygiene. Caregivers should be asked to wear a surgical mask when in the same room as
patient and use hand hygiene every 15-20 min. The greatest risk in COVID-19 is transmission to healthcare workers.
In the SARS outbreak of 2002, 21% of those affected were healthcare workers [31]. Till date, almost 1500
healthcare workers in China have been infected with 6 deaths. The doctor who first warned about the virus has died
too. It is important to protect healthcare workers to ensure continuity of care and to prevent transmission of infection
to other patients. While COVID-19 transmits as a droplet pathogen and is placed in Category B of infectious agents
(highly pathogenic HSN1 and SARS), by the China National Health Commission, infection control measures
recommended are those for

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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). 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

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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/hydroxychloroquine 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

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Animal Models and Cell Cultures

For evaluating the potential of vaccines and therapeutics against CoVs, including SARS-CoV, MERS-CoVs, and the
presently emerging SARS-CoV-2, suitable animal models that can mimic the clinical disease are needed (211, 212).
Various animal models were assessed for SARS- and MERS- CoVs, such as mice, guinea pigs, golden Syrian
hamsters, ferrets, rabbits, nonhuman primates like rhesus macaques and marmosets, and cats (185,213-218). The
specificity of the virus to hACE2 (receptor of SARS-Cov) was found to be a significant barrier in developing animal
models. Consequently, a SARS-CoV transgenic mouse model has been developed by inserting the hACE2 gene into
the mouse genome (219). The inability of MERS-CoV to replicate in the respiratory tracts of animals (mice,
hamsters, and ferrets) is another limiting factor. However, with genetic engineering, 288-330* MERS-CoV
genetically modified mouse model was developed and now is in use for the assessment of novel drugs and vaccines
against MERS-CoV (220). In the past, small animals (mice or hamsters) have been targeted for being closer to a
humanized structure, such as mouse DPP4 altered with human DPP4 (hDPP4), hDPP4-transduced mice, and
hDPP4-Tg mice (transgenic for expressing

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animal species Is necessary to prevent the possibility of virus spread and initiation of an outbreak due to zoonotic
spillover (1). Personal protective equipment (PPE), like face masks, will help to prevent the spread of respiratory
infections like COVID-19. Face masks not only protect from infectious aerosols but also prevent the transmission of
disease to other susceptible individuals while traveling through public transport systems (313). Another critical
practice that can reduce the transmission of respiratory diseases is the maintenance of hand hygiene. However, the
efficacy of this practice in reducing the transmission of respiratory viruses like SARS-CoV-2 is much dependent
upon the size of droplets produced. Hand hygiene will reduce disease transmission only if the virus is transmitted
through the formation of large droplets (314). Hence, it is better not to overemphasize that hand hygiene will prevent
the transmission of SARS-CoV-2, since it may produce a false sense of safety among the general public that further
contributes to the spread of COVID-19. Even though airborne spread has not been reported in SARS-CoV-2
infection, transmission can occur through droplets and fomites, especially when there is close, unprotected contact
between infected and susceptible individuals. Hence, hand hygiene is

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health emergency on 31 January 2020; subsequently, on 11 March 2020, they declared it a pandemic situation. At
present, we are not in a position to effectively treat COVID-19, since neither approved vaccines nor specific
antiviral drugs for treating human CoV infections are available (7-9). Most nations are currently making efforts to
prevent the further spreading of this potentially deadly virus by implementing preventive and control strategies. In
domestic animals, infections with CoVs are associated with a broad spectrum of pathological conditions. Apart from
infectious bronchitis virus, canine respiratory CoV, and mouse hepatitis virus, CoVs are predominantly associated
with gastrointestinal diseases (10). The emergence of novel CoVs may have become possible because of multiple
CoVs being maintained in their natural host, which could have favored the probability of genetic recombination
(10). High genetic diversity and the ability to infect multiple host species are a result of high-frequency mutations in
CoVs, which occur due to the instability of RNA-dependent RNA polymerases along with higher rates of
homologous RNA recombination (10, 11). Identifying the origin of SARS-CoV-2 and the pathogen's evolution will
be helpful for disease surveillance (12), development of

Image 70.

with SARS and MERS (117). SARS-CoV-2 invades the lung parenchyma, resulting in severe interstitial
inflammation of the lungs. This is evident on computed tomography (CT) images as ground-glass opacity in the
lungs. This lesion initially involves a single lobe but later expands to multiple lung lobes (118). The histological
assessment of lung biopsy samples obtained from COVID-19-infected patients revealed diffuse alveolar damage,
cellular fibromyxoid exudates, hyaline membrane formation, and desquamation of pneumocytes, indicative of acute
respiratory distress syndrome (I19). It was also found that the SARS-CoV-2-infected patients often have
lymphocytopenia with or without leukocyte abnormalities. The degree of lymphocytopenia gives an idea about
disease prognosis, as it is found to be positively correlated with disease severity (118). Pregnant women are
considered to have a higher risk of getting infected by COVID-19. The coronaviruses can cause adverse outcomes
for the fetus, such as intrauterine growth restriction, spontaneous abortion, preterm delivery, and perinatal death.
Nevertheless, the possibility of intrauterine maternal-fetal transmission (vertical transmission) is low and was not
seen during either the SARS- or MERS-CoV outbreak (120). However,

Image 71

the comprehensive sequence analysis of the SARS-CoV-2 RNA genome identified that the CoV from Wuhan is a
recombinant virus of the bat coronavirus and another coronavirus of unknown origin. The recombination was found
to have happened within the viral spike glycoprotein, which recognizes the cell surface receptor. Further analysis of
the genome based on codon usage identified the snake as the most probable animal reservoir of SARS-CoV-2 (143).
Contrary to these findings, another genome analysis proposed that the genome of SARS-CoV-2 is 96% identical to
bat coronavirus, reflecting its origin from bats (63). The involvement of bat-derived materials in causing the current
outbreak cannot be ruled out. High risk is involved in the production of bat-derived materials for TCM practices
involving the handling of wild bats. The use of bats for TCM practices will remain a severe risk for the occurrence
of zoonotic coronavirus epidemics in the future (139). Furthermore, the pangolins are an endangered species of
animals that harbor a wide variety of viruses, including coronaviruses (144). The coronavirus isolated from Malayan
pangolins (Manis javanica) showed a very high amino acid identity with COVID-19 at E (100%), M (98.2%), N
(96.7%), and S genes (90.4%). The RBD of S protein

Image 72

other clinical trials in different phases are still ongoing elsewhere.

Immunomodulatory agents. SARS-CoV-2 triggers a strong immune response which may cause cytokine
storm syndrome60,61 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 support146. Tocilizumab and sarilumab, two types of interleukin-6
(1L-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 proinflammatory 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 (REF148),

Image 73

such instance was in 2002-2003 when a new coronavirus of the B genera and with origin in bats crossed over to
humans via the intermediary host of palm civet cats in the Guangdong province of China. This virus, designated as
severe acute respiratory syndrome coronavirus affected 8422 people mostly in China and Hong Kong and caused
916 deaths (mortality rate 11%) before being contained [4]. Almost a decade later in 2012, the Middle East
respiratory syndrome coronavirus (MERS-CoV), also of bat origin, emerged in Saudi Arabia with dromedary camels
as the intermediate host and affected 2494 people and caused 858 deaths (fatality rate 34%) [5]

Origin and spread of COvID-19 1, 2, 6 In December 2019, adults in Wuhan, capital city of Hubei province and a

Image 74

lower respiratory tracts. Acute viral interstitial pneumonia and humoral and cellular immune responses were
observed48,75. Moreover, prolonged virus shedding peaked early in the course of infection in asymptomatic
macaques69, and old monkeys showed severer interstitial pneumonia than young monkeys76, which is similar to what
is seen in patients with COVID-19. In human ACE2-transgenic mice infected with SARS-CoV-2, typ- ical
interstitial pneumonia was present, and viral antigens 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 strain. Golden hamsters also showed typical symptoms after being infected with
SARS-CoV-2 REF77). 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 transmission 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 years9,13,60,80,81, However, clinical manifestations differ with age. In general, older men (>60 years old)
with co-morbidities are more likely to develop severe respiratory disease that requires hospitalization

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helicase activity.

Among the evaluated compounds, 4-(cyclopent1-en-3-ylamino)-5-[2-(4-iodophenyl)hydrazinyl]-4H-1,2,4-triazole-

3-thiol and 4-(cyclopent-1 -en-3-ylamino)-5-[2-(4- chlorophenyl)hydraziny!]-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 discase
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 and strongly neutralizing antibodies
provided considerable protection in mice against a MERS-

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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, he 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). Superspreading 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 superspreading 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).

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Swine acute diarrhea syndrome coronavirus (SADS-CoV) was first identified in suckling piglets having severe
enteritis and belongs to the genus Alphacoronavirus (106). The outbreak was associated with considerable scale
mortality of piglets (24,693 deaths) across four farms in China (134). The virus isolated from the piglets was almost
identical to and had 95% genomic similarity with horseshoe bat (Rhinolophus species) coronavirus HKU2,
suggesting a bat origin of the pig virus (106,134, 135). It is also imperative to note that the SADS-CoV outbreak
started in Guangdong province, near the location of the SARS pandemic origin (134). Before this outbreak, pigs
were not known to be infected with bat-origin coronaviruses. This indicates that the bat-origin coronavirus jumped
to pig by breaking the species barrier. The next step of this jump might not end well, since pigs are considered the
mixing vessel for influenza A viruses due to their ability to be infected by both human and avian influenza A viruses
(136). Similarly, they may act as the mixing vessel for coronaviruses, since they are in frequent contact with both
humans and multiple wildlife species. Additionally, pigs are also found to be susceptible to infection with human
SARS-CoV and MERS-CoV, making this scenario a nightmare (109, 137). It is

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assessed intrauterine vertical transmission of COVID-19 infection in nine infants born to infected mothers, found
that none of the infants tested positive for the virus.45 Likewise, there was no evidence of intrauterine infection
caused by vertical transmission in the SARS and MERS epidemics.43 The CDC asserts that infants born to mothers
with confirmed COVID-19 are considered persons under investigation (PUI) and should be temporarily separated
from the mother and isolated. 46

7.1 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. This includes wearing a facemask and practising hand

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and SARS, along with adopting and strengthening a few precautionary measures owing to the unknown nature of
this novel virus (36, 189). Presently, the main course of treatment for severely affected SARS-CoV-2 patients
admitted to hospitals includes mechanical ventilation, intensive care unit (TCU) admittance, and symptomatic and
Supportive therapies. Additionally, RNA synthesis inhibitors (lamivudine and tenofovir disoproxil fumarate),
remdesivir, neuraminidase inhibitors, peptide (EK1), anti-inflammatory drugs, abidol, and Chinese traditional
medicine (Lianhuaqingwen and ShuFengJieDu capsules) could aid in COVID-19 treatment. However, further
clinical trials are being carried out concerning their safety and efficacy (7). It might require months to a year(s) to
design and develop effective drugs, therapeutics, and vaccines against COVID-19, with adequate evaluation and
approval from regulatory bodies and moving to the bulk production of many millions of doses at commercial levels
to meet the timely demandof mass populations across the globe (9). Continuous efforts are also warranted to identify
and assess viable drugs and immunotherapeutic regimens that revealed proven potency in combating other viral
agents similar to SARS-CoV-2. COVID-19 patients showing severe signs are

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We assessed the nucleotide percent similarity using the MegAlign software program, where the similarity between
the novel SARS-CoV-2 isolates was in the range of 99.4% to 100%. Among the other Serbecovirus CoV sequences,
the novel SARS-CoV 2 sequences revealed the highest similarity to bat- SL-CoV, with nucleotide percent identity
ranges between 88.12 and 89.65%. Meanwhile, earlier reported SARS-CoVs showed 70.6 to 74.9% similarity to
SARS-CoV-2 at the nucleotide level. Further, the nucleotide percent similarity was 55.4%, 45.5% to 47.9%, 46.2%
to 46.6%, and 45.0% to 46.3% to the other four subgenera, namely. Hibecovirus, Nobecovirus, Merbecovirus, and
Embecovirus, respectively. The percent similarity index of current outbreak isolates indicates a close relationship
between SARS-CoV-2 isolates and bat- SL-CoV, indicating a common origin. However, particular pieces of
evidence based on further complete genomic analysis of current isolates are necessary to draw any conclusions,
although it was ascertained that the current novel SARS-CoV-2 isolates belong to the subgenus Sarbecovinus in the
diverse range of betacoronaviruses. Their possible ancestor was hypothesized to be from bat CoV strains, wherein
bats might have played a crucial role in harboring this class of viruses.

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Coronavirus is the most prominent example of a virus that has crossed the species barrier twice from wild animals to
humans during SARS and MERS outbreaks (79, 102). The possibility of crossing the species barrier for the third
time has also been suspected in the case of SARS-CoV-2 (COVID-19). Bats are recognized as a possible natural
reservoir host of both SARS-CoV and MERS-CoV infection. In contrast, the possible intermediary host is the palm
civet for SARS-CoV and the dromedary camel for MERS-CoV infection (102). Bats are considered the ancestral
hosts for both SARS and MERS (103). Bats are also considered the reservoir host of human coronaviruses like
HCoV-229E and HCoV-NL63 (104). In the case of COVID-19, there are two possibilities for primary transmission:
it can be transmitted either through intermediate hosts, similar to that of SARS and MERS, or directly from bats
(103). The emergence paradigm put forward in the SARS outbreak suggests that SARS-CoV originated from bats
(reservoir host) and later jumped to civets (intermediate host) and incorporated changes within the receptor-binding
domain (RBD) to improve binding to civet ACE2. This civet-adapted virus, during their subsequent exposure to
humans at live markets, promoted further adaptations that resulted in the epidemic strain (104). Transmission can
also

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(96.7%), and S genes (904%). The RBD of S protein in CoV isolated from pangolin was almost identical (one amino
acid difference) to that of SARS-CoV-2. A comparison of the genomes suggests recombination between pangolin-
CoV-like viruses with the bat-CoV-RaTG13-like virus. All this suggests the potential of pangolins to act as the
intermediate host of SARS-CoV-2 (145). Human-wildlife interactions, which are increasing in the context of climate
change (142), are further considered high risk and responsible for the emergence of SARS-CoV. COVID-19 is also
Suspected of having a similar mode of origin. Hence, to prevent the occurrence of another zoonotic spillover (1),
exhaustive coordinated efforts are needed to identify the high-risk pathogens harbored by wild animal populations,
conducting surveillance among the people who are susceptible to zoonotic spillover events (12), and to improve the
biosecurity measures associated with the wildlife trade (146). The serological surveillance studies conducted in
people living in proximity to bat caves had earlier identified the serological confirmation of SARS-related CoVs in
humans. People living at the wildlife-human interface, mainly in rural China, are regularly exposed to SARS-related
CoVs (147). These findings will not have any significance until a

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amnotransierase, bilirubin, and, especialiy, D-uiimer (244). 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 n patien 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 (123).

CORONAVIRUSES IN ANIMALS AND ZOONOTIC LINKS-A BRIEF 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 (20, 30, 79,

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Origin and Spread of COVID-19 [1,2, 6]

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 1st 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

Image 85

involved in the COVID-19 outbreak is of great importance, because the strain on their mental wellbeing will affect
their attention, concentration, and decision-making capacity. Hence, for control of the COVID-19 outbreak, rapid
steps should be taken to protect the mental health of medical workers (229). Since the living mammals sold in the
wet market are suspected to be the intermediate host of SARS CoV-2, there is a need for strengthening the
regulatory mechanism for wild animal trade (13). The total number of COVID-19 confirmed cases is on a
continuous rise and the cure rate is relatively low, making disease control very difficult to achieve. The Chinese
government is making continuous efforts to contain the disease by taking emergency control and prevention
measures. They have already built a hospital for patients affected by this virus and are currently building several
more for accommodating the continuously increasing infected population (230). The effective control of SARS
CoV-2/COVID-19 requires high-level interventions like intensive contact tracing, as well as the quarantine of
people with suspected infection and the isolation of infected individuals. The implementation of rigorous control and
preventive measures together might control the Ro number and reduce the transmission risk (228). Considering the
zoonotic

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route warrants the introduction of negative fecal viral nucleic acid test results as one of the additional discharge
criteria in laboratory-confirmed cases of COVID-19 (326). The COVID-19 pandemic does not have any novel
factors, other than the genetically unique pathogen and a further possible reservoir. The cause and the likely future
outcome are just repetitions of our previous interactions with fatal coronaviruses. The only difference is the time of
occurrence and the genetic distinctness of the pathogen involved. Mutations on the RBD of CoVs facilitated their
capability of infecting newer hosts, thereby expanding their reach to all corners of the world (85). This is a potential
threat to the health of both animals and humans. Advanced studies using Bayesian phylogeographic reconstruction
identified the most probable origin of SARS-CoV-2 as the bat SARS-like coronavirus, circulating in the
Rhinolophus bat family (86).

Phylogenetic analysis of 10 whole-genome sequences of SARS-CoV-2 showed that they are related to two CoVs of
bat origin, namely, bat-SL-CoVZc45 and bat-SL-CoVZXC21, which were reported during 2018 in China (17). It
was reported that SARS-CoV-2 had been confined to use ACE2 as an entry receptor while exhibiting an RBD
similar

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and Middle East respiratory syndrome coronavirus (MERS-CoV), but has lower fatality. The global impact of this
new epidemic is yet uncertain.

Keywords: 2019-nCOV, SARS-CoV-2, COVID-19, Pneumonia, Review

Introduction

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]. Til os/03/2020 around 96,000 cases of coronavirus disease 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. This article gives a bird's eye view about

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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.53-65 Hydroxychloroquine 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 immunomodulating agent used as adjunct therapy in some
protocols based on a theoretical mechanism and limited preliminary data. 66

15 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 on

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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 li-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 atenuated 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.

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10 RECOMBINANT SUBUNIT VACCINE

Clover Biopharmaceuticas 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.

11 CLINICAL MANAGEMENT AND 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. 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

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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).

VACCINES, THERAPEUTICS, AND DRUGS

Recently emerged viuses, 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 therapeutics, and drug regimens
to counter emerging

Image 92
(181). CEPI has also funded Moderna to develop a vaccine for COVID-19 in partnership with the Vaccine Research
Center (VRC) of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of
Health (NIH) (182). By employing mRNA vaccine platform technology, a vaccine candidate expressing SARS-
CoV-2 spike protein is likely to go through clinical testing in the coming months (180). On 16 March 2020, Jennifer
Haller became the first person outside China to receive an experimental vaccine, developed by Moderna, against this
pandemic virus. Moderna, along with China's CanSino Biologics, became the first research group to launch small
clinical trials of vaccines against COVID-19. Their study is evaluating the vaccine's safety and ability to trigger
immune responses (296). Scientists from all over the world are trying hard to develop working vaccines with robust
protective immunity against COVID-19. Vaccine candidates, like mRNA-1273 SARS-CoV-2 vaccine, IN0-4800
DNA coronavirus vaccine, and adenovirus type 5 vector vaccine candidate (Ad5-nCoV), are a few examples under
phase I clinical trials, while self-amplifying RNA vaccine, oral recombinant COVID-19 vaccine, BNT162, plant-
based COVID-19 vaccine, and li-Key peptide COVID-19 vaccine are

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14 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

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The results of the studies related to SARS-CoV-2 viral loads reflect active replication of this virus in the upper
respiratory tract and prolonged viral shedding after symptoms disappear, including via stool. Thus, the current case
definition needs to be updated along with a reassessment of the strategies to be adopted for restraining the SARS-
CoV-2 outbreak spread (248). In some cases, the viral load studies of SARS-CoV-2 have also been useful to
recommend precautionary measures when handling specific samples, e.g., feces. In a recent survey from 17
confirmed cases of SARS-CoV-2 infection with available data (representing days 0 to 13 after onset), stool samples
from nine cases (53%; days 0 to 11 after onset) were positive on RT-PCR analysis. Although the viral loads were
lower than those of respiratory samples (range, 550 copies per ml to 1.21 x 105 copies per ml), this has essential
biosafety implications (151).

The samples from 18 SARS-CoV-2-positive patients in Singapore who had traveled from Wuhan to Singapore
showed the presence of viral RNA in stool and whole blood but not in urine by real-time RT-PCR 288). Further,
novel SARS-CoV-2 infections have been detected in a variety of clinical specimens, like bronchoalveolar lavage
fluid,

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wearing a facemask and practising 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.42

7.2 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 hospitalisation, 11-31% of them required admission to the intensive care unit, and 4-11% died. 50

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All clinicians should keep themselves updated about recent developments including global spread of the disease.
Non-essential international travel should be avoided at this time. People should stop spreading myths and false
information about the disease and try to allay panic and anxiety of the public.

Conclusions
This new virus outbreak has challenged the economic, medical and public health infrastructure of China and to some
extent, of other countries especially, fits neighbors. 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. efforts should be made to

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assays offer high accuracy in the diagnosis of SARS-CoV-2, but the current rate of spread limits its use due to the
lack of diagnostic assay kits. This will further result in the extensive transmission of COVID-19, since only a
portion of suspected cases can be diagnosed. In such situations, conventional serological assays, like enzyme-linked
immunosorbent assay (ELISA), that are specific to COVID-19 IgM and IgG antibodies can be used as a high-
throughput alternative (149). At present, there is no diagnostic kit available for detecting the SARS-CoV-2 antibody
(150). The specific antibody profiles of COVID-19 patients were analyzed, and it was found that the IgM level
lasted more than 1 month, indicating a prolonged stage of virus replication in SARS-CoV-2-infected patients. The
IgG levels were found to increase only in the later stages of the disease. These findings indicate that the specific
antibody profiles of SARS-CoV-2 and SARS-Cov were similar (325). These findings can be utilized for the
development of specific diagnostic tests against COVID-19 and can be used for rapid screening. Even though
diagnostic test kits are already available that can detect the genetic sequences of SARS-COV. 2 (95), their
availability is a concern, as the number of COVID-19 cases is skyrocketing (155, 157). A major problem associated
with this diagnostic kit is

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infected by human beings. However, evidence of cat- to-human transmission is lacking and requires further studies
(332). Rather than waiting for firmer evidence on animal-to-human transmission, necessary preventive measures are
advised, as well as following social distancing practices among companion animals of different households (331).
One of the leading veterinary diagnostic companies, IDEXX, has conducted large-scale testing for COVID-19 in
specimens collected from dogs and cats. However, none of the tests turned out to be positive (334). In a study
conducted to investigate the potential of different animal species to act as the intermediate host of SARS-CoV-2, it
was found that both ferrets and cats can be infected via experimental inoculation of the virus. In addition, infected
cats efficiently transmitted the disease to naive cats (329). SARS-CoV-2 infection and subsequent transmission in
ferrets were found to recapitulate the clinical aspects of COVID-19 in humans. The infected ferrets also shed virus
via multiple routes, such as saliva, nasal washes, feces, and urine, post infection, making them an ideal animal
model for studying disease transmission (337). Experimental inoculation was also done in other animal species and
found that the dogs have low susceptibility, while the chickens,

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6.3 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 thee practising clinicians by assisting them in diagnosis. Similarly, there are
studies published on COVID-19 which are comprised of the serological data on clinical samples. 38, 39

6.4 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

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performance (Table 2) (80, 245, 246). The viral loads of SARS-CoV-2 were measured using N-gene- specific
quantitative RT-PCR in throat swab and sputum samples collected from COVID-19-infected individuals. The results
indicated that the viral load peaked at around 5 to 6 days following the onset of symptoms, and it ranged from 10 4 to
107 copies/ml during this time (151). In another study, the viral load was found to be higher in the nasal swabs than
the throat swabs obtained from COVID-19 symptomatic patients (82). Although initially it was thought that viral
load would be associated with poor outcomes, some case reports have shown asymptomatic individuals with high
viral loads (247). Recently, the viral load in nasal and throat swabs of 17 symptomatic patients was determined, and
higher viral loads were recorded soon after the onset of symptoms, particularly in the nose compared to the throat.
The pattern of viral nucleic acid shedding of SARS-CoV-2-infected patients was similar to that of influenza patients
but seemed to be different from that of SARS-CoV patients. The viral load detected in asymptomatic patients
resembled that of symptomatic patients as studied in China, which reflects the transmission perspective of
asymptomatic or symptomatic patients having minimum signs and symptoms (82). Another study,