Understand COVID-19

What is SARS-CoV-2 and COVID-19?

A new strain of a highly contagious coronavirus, similar to SARS-CoV, was identified in Wuhan, China, in December 2019. This new strain is known as SARS-CoV-2 and causes the disease COVID-19. SARS-CoV-2 is NOT the same as the coronaviruses that cause mild illness, such as the common cold. It is spread from person to person through respiratory droplets (i.e., cough, sneezes, talks) produced from an infected person.

On March 11, 2020, COVID-19 was declared a pandemic by the World Health Organization (WHO). The disease had spread across several countries and affected many people. On March 13, 2020, a national emergency was declared in the United States concerning the COVID-19 outbreak. The WHO and CDC have recommended face masks and social distancing (6 ft, or 2 m) to mitigate the spread of COVID-19.

SARS-CoV-2: An Overview of Virus Structure, Transmission and Detection

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is an enveloped, single-stranded RNA virus of the family Coronaviridae. The members of the family Coronaviridae are enveloped and positive stranded RNA viruses that share structural similarities and are composed of 16 non-structural proteins and 4 structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N). Coronaviruses cause diseases with symptoms ranging from those of a mild common cold to more severe ones such as COVID-19 caused by SARS-CoV-21,2.

SARS-CoV-2 is transmitted from person-to-person primarily via respiratory droplets, while indirect transmission through contaminated surfaces is also possible3,4,5. The incubation period for COVID-19 ranges from 2-14 days following exposure. Most cases show symptoms approximately 4-5 days after exposure 6,7,8. The spectrum of symptomatic infection ranges from mild characterized by fever, cough, fatigue, loss of smell and taste, shortness of breath to critical, which may require hospitalization9,10. While most COVID-19 symptomatic cases are not severe, severe illness occurs predominantly in adults with underlying medical conditions or advanced age and requires intensive care. Critical cases requiring intensive care are characterized by e.g., respiratory failure, shock and/or multiple organ dysfunction, or failure9,11,12.

When infected with SARS-CoV-2, the immune system mounts an immune response, including production of specific antibodies against viral antigens. Both IgM and IgG have been detected as early as day 5 after symptom occur13, 14. Anti-SARS-CoV-2 IgM and IgG often appear simultaneously, and some cases have been reported where IgG appears before IgM, limiting its diagnostic utility14,15.

References

1) Su, S. et al. (2016). Trends Microbiol. 24(6), 490-502.
2) Zhu, N. et al. (2020). N Engl J Med. 382(8), 727-733.
3) J, Liao X (2020). Emerg Infect Dis. 26(6): Epub ahead of print. doi: http://dx.doi.org/10.3201/eid2606.200239/PubMed
4) Chan JF (2020). Lancet. 395(10223), 514–23.
5) Ong SWX (2020). JAMA. Epub ahead of print. http://dx.doi.org/10.1001/jama.2020.3227  PubMed
6) Chan, J.F. et al. (2020). Lancet. 395, 514-523
7) WHO. https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200403- sitrep-74-covid-19-mp.pdf. Published April 3, 2020. Accessed April 15, 2020.
8) Lauer, S.A. et al. (2020). Ann Intern Med. 172(9), 577-82.
9) Rothe, C. et al. (2020). N Engl J Med. 382(10), 970-971.
10) Kupferschmidt, K. Study claiming new coronavirus can be transmitted by people without symptoms was flawed. Science. https://www.sciencemag.org/news/2020/02/paper-non-symptomatic-patient-transmitting-coronavirus-wrong. Published February 4, 2020. Accessed April 15, 2020.
11) Bai, Y. et al. (2020). JAMA. 323(14), 1406-1407.
12) Mizumoto, K. et al. (2020). Euro Surveill. 25(10), 2000180.
13) Liu, W. et al. (2020). J Clin Microbiol. 58(6), e00461-2.
14) To, K. et al. (2020). Lancet Infect Dis. 20(5), 565-74.
15) Long, Q. et al. (2020). medRxiv. https://doi.org/10.1101/2020.03.18.20038018.