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 Table of Contents  
Year : 2020  |  Volume : 6  |  Issue : 1  |  Page : 3-10

Understanding the unusual viral outbreak: Coronavirus disease 2019

1 Rangaraya Medical College, East Godavari District, Andhra Pradesh, India
2 Konaseema Institute of Medical Sciences and Research Foundation, Amalapuram, Andhra Pradesh, India
3 Department of Community Medicine, Government General Hospital, East Godavari District, Andhra Pradesh, India
4 Jawaharlal Nehru Medical College, Wardha, Maharashtra, India

Date of Submission03-May-2020
Date of Decision08-May-2020
Date of Acceptance26-May-2020
Date of Web Publication20-Jul-2020

Correspondence Address:
Tarun Kumar Suvvari
Rangaraya Medical College, Near Bhanugudi Junction, Opposite JNTU, Kakinada, East Godavari District - 533 001, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrsm.jcrsm_30_20

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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the respiratory coronavirus disease 2019 (COVID-19). Coronaviruses are a large family of enveloped, positive-sense, single-stranded RNA viruses, which infect a broad range of vertebrate animals. The SARS-CoV-2 is spread primarily between people through close contact and through respiratory droplets produced from coughs or sneezes by the infected individuals. After entering into the human body, it enters human cells by binding to the angiotensin-converting enzyme 2 receptors, prominently present in lung, kidney, and gastrointestinal tract. Older people and people of all ages with severe chronic medical conditions such as diabetes, lung disease, and heart disease seem to be at higher risk of developing serious COVID-19 illness. There have been four pandemics caused by the emergence of new influenza viruses in the past century such as H1N1 Spanish flu (1918), H2N2 Asian flu (1957), the H3N2 Hong Kong flu (1968), and the H1N1 Swine flu (2009). Community interventions are important response strategies that can reduce the impact of disease. Widespread transmission of the virus could translate the situation into large numbers of people needing medical care at the same time. Better understanding of the complexity and dynamics of influenza pandemics reduces the further risk effect of such critical situations. Global efforts in tackling the virus at this time are focused all together on lessening the spread and impact of this virus.

Keywords: Coronavirus disease 2019, coronavirus, severe acute respiratory syndrome coronavirus-2

How to cite this article:
Suvvari TK, Simhachalam Kutikuppala LV, Babu G K, Jadhav M. Understanding the unusual viral outbreak: Coronavirus disease 2019. J Curr Res Sci Med 2020;6:3-10

How to cite this URL:
Suvvari TK, Simhachalam Kutikuppala LV, Babu G K, Jadhav M. Understanding the unusual viral outbreak: Coronavirus disease 2019. J Curr Res Sci Med [serial online] 2020 [cited 2022 Dec 8];6:3-10. Available from: https://www.jcrsmed.org/text.asp?2020/6/1/3/290248

  Introduction Top

The coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) previously known as 2019 novel coronavirus (2019-nCoV). International Committee on Taxonomy of Viruses on February 11, 2020, announced the name as SARS-CoV-2 because the genetic material of coronavirus responsible for the SARS outbreak in 2003 and 2019-nCoV is similar to each other.[1],[2]

However, using the name SARS may lead to needless panic among people mainly in Asian continent as they were already affected by the SARS outbreak in 2003. Hence, the World Health Organization (WHO) has decided to refer to the virus as COVID-19 or the virus responsible for COVID-19.[2]

Pneumonia of unknown cause was detected in Wuhan city in China and was first reported to the WHO Country Office in China on December 31, 2019. This was the start to the alarming pandemic. On January 7, 2020, the causative virus was identified as novel beta-coronavirus (CoV) of the same subgenus as SARS-CoV by Chinese authorities. China shared the nCoV genetic sequence to other countries for developing specific diagnostic kits on January 12, 2020.[1]

The outbreak was declared as a public health emergency of international concern (PHIEC) on January 30, 2020. This is the sixth time that the WHO has declared a PHEIC since the International Health Regulations came into force in 2005. The outbreak was declared as a pandemic on March 11, 2020. It is the first time the WHO has called an outbreak a pandemic since the H1N1 “swine flu” in 2009.[1],[3]

By April 6, 2020, 1,210,956 confirmed cases and 67,594 deaths were reported globally. The current mortality rate of COVID-19 is 5.58% globally. This article offers an overall perspective about COVID-19. Readers must update themselves with information on COVID-19 due to its continuous evolution,[4]

  Virology Top

CoVs are positive-sense single-stranded RNA viruses. They are enveloped viruses with a helical nucleocapsid. The diameter is 60–140 nm approximately. There is no virion polymerase. In electron microscope, prominent club-shaped spikes in the form of crown (in Latin coronam means crown) can be seen. The spikes are made up of glycoproteins.[5]

CoVs belong to the Order – Nidovirales, Family – Coronaviridae, Subfamily – Orthocoronavirinae. The four genera of CoVs are – alpha-CoV, beta-CoV, delta-CoV, and gamma-CoV. Beta-CoV further has five subgenera or lineages. Till date, seven human CoVs are discovered.[6]

  • HCoV-OC43 and HCoV-HKU1 are beta-CoV of lineage A
  • HCoV-229E and HCoV-NL63 are alpha-CoV
  • SARS-CoV and SARS-CoV-2 are beta-CoV of lineage B
  • Middle East respiratory syndrome (MERS)-CoV is beta-CoV of lineage C.

Most research studies based on genomic characterization of COVID-19 reveal the gene sources of alpha-CoV and beta-CoV. The two main sero types are 229E and OC43. The genome of 2019-nCoV has nucleotide identity of 89% with bat SARS-like CoVZXC21 and 82% with human SARS-CoV.[7]

The full-length genome sequence of COVID-19 and other available genomes of beta-CoV showed that the closest relationship was with the bat SARS-like CoV strain Bat CoV RaTG13 with an identity of 96%. Hence, the study reveals that SARS-CoV-2 may evolved from bats.[8]

  History Top

In the past two decades, there were two incidents where major outbreaks occurred due to CoVs.

The SARS outbreak occurred between November 2002 and July 2003. It was caused by SARS-CoV and led to 8422 people being infected, with 916 deaths and a mortality rate of 11%. The virus mainly affected people in South China and Hong Kong. The virus was reported to have been transported to humans from civets.[9],[10]

The MERS outbreak took place in September 2012 and was caused by MERS-CoV. A total of 2494 cases with 858 deaths were reported globally, with a mortality rate of 34.4%. A majority of the cases were from Saudi Arabia and the virus was transmitted to humans from dromedary camels.[11],[12]

  Epidemiology Top

The current outbreak of COVID-19 originated in Wuhan city, Hubei province, China, in December 2019 as a cluster of pneumonia cases of unknown cause. Most of the patients were operating dealers or vendors in the Huanan seafood market. On December 31, 2019, severe cases of pneumonia were reported to the China National Health Commission.[13],[14]

Huanan seafood wholesale market was closed on January 1, 2020, as environmental swabs taken from the seafood market showed positive results, indicating that the virus may have originated from there. It supported the theory that 2019-nCoV is a zoonotic virus but the animal source had not been identified. On January 11, 2020, the first death due to COVID-19 was reported in China.[13],[14]

Large scale people migration around the Chinese New Year contributed to the coronavirus outbreak. The number of cases rose exponentially and human to human tranmission was confimed in China by january 2020. Cases in countries other than Cina were reported in people with a travel history to Wuhan.[13],[14]

The first case was confirmed in Thailand on January 8, 2020; in Nepal on January 13, 2020; and in Japan on January 14, 2020. A total of 319 cases of 2019-nCoV were reported outside of China as of February 10, 2020. On February 3, 2020, an outbreak of COVID-19 on Cruise Ship Diamond Princess was reported.[14],[15]

Many countries had put screening mechanisms in airports to detect the people with COVID-19 symptoms, placing them in isolation, and testing them for COVID-19. From December 31, 2020, to February 11, 2020, a total of 43,101 confirmed cases and 1018 (2%) deaths were reported globally, in which 7333 patients are reported as severe (17%).[13],[14]

The meeting of first emergency committee was conducted on January 22 and 23, 2020. In India, the first case was reported in India on January 30, 2020. On January 31, 2020, Italy confirmed first positive having a travel history from Wuhan.[13],[14]

On March 11, 2020, the WHO declared COVID-19 as pandemic. By March 15, Italy had 21,157 confirmed cases with 1441 deaths, declaring it a national emergency.[3],[13]

By April 6, 2020, 1,210,956 confirmed cases and 67,594 deaths were reported globally affecting 209 countries and territories around the world and two international conveyances: The Diamond Princess Cruise ship in Japan and MS Zaandam Cruise ship in America.[4],[16]

By April 6, 2020, the USA became the most affected country with 369,522 positive cases followed by Spain with 140,510 positive cases and Italy in the third position with 132,547 positive cases. China held the sixth position with 81,740 positive cases with the highest recovered cases of 77,167 (94%).[5] The current mortality rate of COVID-19 is 5.58% globally.[16]

By April 6, India had 4789 positive cases with 124 deaths in 31 states and union territories; Maharashtra with the highest number of 868 positive cases followed by Tamil Nadu with 621 positive cases.[17]

  Spread and Transmission Top

  • From person to person – It is mainly transmitted by the respiratory aerosol when infected person speaks, coughs, or sneezes and between people who are in close contact (generally within 6 feet)
  • From contact with contaminated surfaces or objects
  • Fecal transmission of COVID-19 can occur, but its contribution is low.[18],[19]

Infection can be transmitted by asymptomatic people before onset of symptoms through large droplets generated during coughing and sneezing. However, it is significant that the infection appears to have been transmitted during the incubation period. The fact that asymptomatic persons are the potential sources of 2019-nCoV infection may warrant a reassessment of transmission dynamics of the current outbreak.[20],[21]

The main fear is about the community spread of the COVID-19 which may lead to huge death tolls, especially in India. Community spread means that people have been infected with the virus in an area, including some who are not sure how or where they became infected.[22],[23]

There is no evidence that companion animals such as dogs or cats can be infected with the nCoV. However, on March 16, 2020, a dog that died in Hongkong tested positive for COVID-19. SARS-CoV-2 can be transmitted in all areas, irrespective of climatic conditions. The SARS-CoV-2 cannot be transmitted through the mosquito bite.[24],[25]

Some research studies showed that there is no evidence for the intrauterine or transplacental transmission of SARS-CoV-2 from infected mothers to their progeny. The infected women can breast feed their babies as there is no evidence that COVID-19 can be transmitted through the breast milk.[26],[27]

The people of healthcare department and medical care workers are at high risk due to the close contact with infected patients. There could be chance of transmission of COVID-19 from dead body to family members and health workers. Standard precautions should be followed by healthcare workers while handling dead bodies of COVID-19.[28]

Smokers are prone to get infected with COVID-19 as the act of smoking means that fingers (and possibly contaminated cigarettes) are in contact with lips which increase the possibility of transmission of virus from hand to mouth. Smokers may also already have lung disease or reduced lung capacity which would greatly increase risk of serious illness. Smoking increases oxygen needs and reduces the ability of the body to use oxygen properly that put infected people at higher risk of serious lung conditions such as pneumonia.[29]

  Pathogenesis and Pathophysiology Top

People of all ages can be infected by the nCoV-2019, but individuals at highest risk for severe disease and death include people aged over 60 years and those with underlying conditions such as hypertension, diabetes, cardiovascular diseases, chronic respiratory diseases, and cancer. Disease in children appears to be relatively rare and mild with low number of cases reported among individuals aged<18 years.[30]

SARS-CoV-2 attacks primarily ciliated bronchial epithelial cells and type-2 pneumocytes. The binding of the SARS-CoV-2 to angiotensin-converting enzyme-2 (ACE-2) on the surface of respiratory epithelium may contribute to dysregulation of fluid balance that causes edema in the alveolar space. MERS-CoV binds to CD26 on the respiratory mucosa.[31]

CoV infection is typically limited to the mucosal cells of the respiratory tract. Many are asymptomatic and may play a role in spread of infection. Pneumonia caused by the SARS-CoV is characterized by the diffuse edema, resulting in hypoxia.[31]

The genomic data of the nCoV responsible for COVID-19, SARS CoV-2 show that its spike protein contains some unique adaptations. One of these adaptations provides special ability of this CoV to bind to a specific protein on human cells called ACE2. SARS-CoV-2 binds to target cells through ACE2, which is expressed in the lungs. The virus accesses host cells through the enzyme ACE2, which is most abundant in the type II alveolar cells of the lungs; hence, lungs are the organs most affected by COVID-19. The virus also affects gastrointestinal organs as ACE2 is abundantly expressed in the glandular cells of gastric, duodenal, and rectal epithelium as well as endothelial cells and enterocytes of the small intestine.[32],[33]

Some research studies revealed that there are higher viral loads in the nose than in the throat. There is no difference in the viral loads between symptomatic and asymptomatic patients, which suggests the transmission potential of asymptomatic or mild symptomatic patients.[34]

Incubation period means the time between entry of the virus into the body and beginning of symptoms of the disease. Most of the research articles stated that the incubation period of COVID 19 is between 1 to 14 days.[35]

The basic reproductive number (R0) of COVID-19 is higher than SARS and MERS. The estimated average range is from 2.0 to 6.47 according to various modeling studies.[36]

The autopsy report of COVID-19 patients reveals that the histological examination of the lung showed bilateral diffuse alveolar damage with interstitial fibrosis, fibromyxoid exudation, and infiltrated immune cells in the alveoli. Most of the infiltrated cells are macrophages, monocytes, and CD4-postive cells. The lung showed evident desquamation of type 2 pneumocytes and hyaline membrane formation, indicating acute respiratory distress syndrome. Moderate amount of multinucleated giant cells, lymphocytes, eosinophils, and neutrophils were also observed. While the 2019-nCoV mainly affects the lungs, the infection may involve in the damage of heart, blood vessels, liver, kidney, and other organs.[37]

The pathogenesis and pathophysiology are explained in [Figure 1] as flowchart.[32],[38]
Figure 1: Pathogenesis and pathophysiology of coronavirus disease 2019

Click here to view

  Clinical Signs and Laboratory Findings Top

People infected with COVID-19 generally develop signs and symptoms, including mild respiratory symptoms and fever; on an average of 5–6 days after infection (mean incubation period 5–6 days, range 1–14 days). The symptoms of COVID-19 are nonspecific and can range from asymptomatic to pneumonia and death.[39]

According to the Report of WHO-China Joint Mission on COVID-19, the typical symptoms are presented in [Table 1].[40]
Table 1: Typical symptoms of COVID 19

Click here to view

Other symptoms include nasal congestion, nausea or vomiting, anorexia, diarrhea, myalgia, and hemoptysis. Some COVID-19-infected patients show unusual symptoms such as anosmia (lack of sense of smell), dysgeusia (lack of sense of taste), and conjunctivitis.[40],[41]

Laboratory findings of COVID-19 patients are presented in [Table 2].[42],[43]
Table 2: Laboratory findings of COVID-19 patients

Click here to view

People infected with COVID may be classified as:[44]

  1. Mild type shows mild clinical symptoms and does not show any pneumonia in computed tomographic (CT) scan
  2. Common type shows fever and respiratory tract symptoms and shows pneumonia in the CT scan
  3. Severe type shows respiratory distress and low oxygen saturation
  4. Critical type shows respiratory failure and shock leading to organ failure which requires mechanical ventilation and intensive care unit monitoring.

  Diagnosis Top

Diagnosis of COVID-19 is mainly based on epidemiological history, clinical manifestations and laboratory testing in the form of Nucleic acid detection. CT chest may often be contributory.[33]

The two commonly used nucleic acid detection technologies for SARS-CoV-2 are real-time quantitative polymerase chain reaction (RT-qPCR) and high-throughput sequencing. RT-qPCR is the most common, effective, straightforward method for detection.[45]

The WHO suggest collecting the specimens from both the upper respiratory tract (naso and oropharyngeal samples) and lower respiratory tract, such as expectorated sputum, endotracheal aspirate, or bronchoalveolar lavage. The samples must be stored at 4°C. The genetic material extracted from the saliva or mucus sample is amplified through the reverse polymerase chain reaction which provide results in 4–6 h.[46]

CT scans have a great clinical diagnostic value for COVID-19. High-resolution CT of the chest is useful for early diagnosis and evaluation of disease severity of patients. The typical CT images show bilateral pulmonary parenchymal ground-glass and consolidative pulmonary opacities, sometimes with a rounded morphology and a peripheral lung distribution.[47]

Differential diagnosis

It includes the all viral, bacterial, and fungal infections infecting the respiratory system of humans. In imaging diagnosis, it is difficult to distinguish COVID-19 from the pneumonias caused by influenza A and B virus, cytomegalovirus, adenovirus, and other viral and bacterial pneumonias. We also need to differentiate the COVID-19 from bacterial pneumonia, mycoplasma pneumonia, and chlamydia pneumonia.[48]

Pathogenic factors, first symptoms, travel history, laboratory examination, and chest CT manifestations play a key role in confirmation of COVID-19 disease. The travel history has a major role; we should confirm that the suspect has a foreign travel history or to areas having local and community transmission or contact with patients with foreign travel history or contact with COVID-19-infected patients.[49]

  Treatment Top

According to the WHO, the Centers for Disease Control and Prevention (CDC), and the FDA, there are currently no medications or vaccines proven to be effective for the treatment or prevention of SARS-CoV-2.[50]

Small studies in France, China, and South Korea revealed that the patients who received a combination of hydroxychloroquine and azithromycin tested negative and were virologically cured within 6 days of treatment.[51],[52],[53]

Other drugs such as rintatolimod, azvudine, danoprevir, plitidepsin, Sarilumab and tocilizumab (interleukin-6 inhibitors) are in experimental stages and convalescent plasma and corticosteroids have shown promise so far in the treatment of COVID-19.[50]

Some vaccines that are in clinical trials are presented in [Table 3].[50]
Table 3: Some vaccines that are in clinical trials

Click here to view

The WHO recommended to avoid the use of ibuprofen and similar anti-inflammatory drugs as they can act as “an aggravating factor” in COVID-19 infections.[54]

  Prevention and Control Top

Extensive measures to reduce person-to-person transmission of COVID-19 are to control the outbreak, which can include social distancing, self-quarantine, and lockdown. Self-quarantine is the individual and impactful approach in the early prevention of infection. It also helps in breaking the chain of transmission.[55]

Special efforts and attention to reduce transmission and provide protection should be applied in susceptible populations, including children, healthcare providers, and elderly people. Possibly due to a weak immune system that permits faster progression of viral infection, the early death cases of COVID-19 outbreak occurred primarily in the elderly people.[56]

How can we prevent ourselves from coronavirus disease 2019?[57]

  • Wash your hands regularly with soap and water or clean them with alcohol-based hand rub
  • Maintain at least 1-m distance between you and people coughing or sneezing
  • Avoid touching your face
  • Cover your mouth and nose when coughing or sneezing
  • Stay home if you feel unwell
  • Wear a mask while going out or interacting with other people as there is shortage of masks for healthcare workers
  • Refrain from smoking and other activities that weaken the lungs
  • Practice physical distancing by avoiding unnecessary travel and staying away from large groups of people
  • Clean and disinfect the frequently touched surfaces daily.

Doctors and healthcare workers are at the frontline of any outbreak response and as such are exposed to hazards that put them at risk of infection to COVID-19. They must wear personal protective equipment (PPE), N-95 masks, surgical masks, gloves, goggles, and gowns while dealing with the COVID-19-infected patients. They must perform hand hygiene with alcohol-based hand rub before and after all patient contact, contact with potentially infectious material, and before putting on and upon removal of PPE, including gloves. Use soap and water if hands are visibly soiled.[58]

  Conclusion Top

As the COVID-19 is a pandemic, every human must take part to fight against this global threat by following personal hygiene, self- and mandatory quarantine, and social distancing.

A vigorous approach needs to be taken with patients who are critically ill with SARS-CoV-2, including ventilator support. Dynamic investment in public health, critical care infrastructure, and capacity is crucial to respond effectively to epidemics and pandemics like COVID-19. It is critical to improve international surveillance, control, cooperation, coordination, and communication about this major outbreak and to be even better prepared to respond to future new public health threats.

People's cooperation and support also play a major role in tackling these disease conditions; the further spread of virus is in the hands of people only. Finally, “Stay-Quarantined – Stay Safe.”

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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