An overview of coronaviruses including the SARS-2 coronavirus - Molecular biology, epidemiology and clinical implications

Abstract

Coronavirus infections have emerged as epidemic and pandemic threats in last two decades. After the H1N1 influenza pandemic in 2009, recently diagnosed novel betacoronavirus or severe acute respiratory syndrome coronavirus (SARS-CoV)-2 has spread across 203 countries and territories in all 5 major continents. World Health Organization (WHO) declared this as a public health emergency of international concern on January 30, 2020. Subsequently on February 11, 2020 a new name was given to this disease i.e. COVID-19 by an expert group from WHO. As of April 12, 2020, 10:00 CET, GMT+2:00, 1,696,588 confirmed cases and 105,952 confirmed deaths have been reported to the WHO. (Coronavirus disease 2019, situation report 83). It possibly originated from a small animal market in Wuhan, China. A cluster of patients were admitted with unusual pneumonia not responding to treatment in various hospitals. Epidemiological, genomic analysis and correlation with other coronaviruses led to the isolation of new coronavirus, closely resembling the bat coronaviruses, from such patients in Wuhan. They were identified as the SARS-CoV-2. This virus infection presents as influenza like illness in the affected people. Fever, cough, respiratory distress with fatigue, diarrhea, nausea and vomiting are common symptoms seen in adults. This may progress on to severe respiratory distress, hypoxia, need for oxygen supplementation and ventilator support as seen in patients in the SARS-CoV-1 epidemic (2003) in Guangdong, China. The transmissibility of SARS-CoV-1 was less as compared to SARS-CoV-2 infection, and it was well controlled with good public health efforts. The present COVID-19 epidemic is still in the acceleration phase of 3 and 4 in various countries. Without any effective antiviral agents available at present, the need of the hour is early case detection, isolation of cases, use of good preventive care measures by the household contacts and in the hospital set up. The results of ongoing clinical trials on hydroxychloroquine, azithromycin alone or in combination and a new antiviral agent remdesivir may help to treat some of the infections. A need for effective vaccine is being seen an as good preventive strategy in this pandemic. However the results of clinical trials and incorporation of vaccines in public health programs is a long way to go.

Keywords: Betacoronavirus; COVID-19; Coronavirus; SARS-CoV-1; SARS-CoV-2; Wuhan.

Fig. 1

The total no. of COVID-19 cases in the continents (China and other countries) as on April 12, 2020. Cases reported in accordance with the applied case definition and testing strategies in the affected countries. https://www.ecdc.europa.eu/geographical distribution-2019-ncov-cases.

Fig. 2

Distribution of COVID-19 deaths in all continents as on 12 April 2020. Deaths reported in accordance with the applied case definition and testing strategies in the affected countries. https://www.ecdc.europa.eu/geographicaldistribution-2019-ncov-deaths.

Fig. 3

Geographical distribution of COVID-19 cases world wide as of 12 April 2020. ECDC data.

Fig. 4

a) Diagrammatic expression of a coronavirus virion: Various structural proteins which form the coronavirus particle and the genome, single stranded RNA are shown. (Adapted from Li G, et al. Journal of Medical Virology, 25 January 2020). b) Artistic impression of coronavirus virions developed from an electron micrograph.

Fig. 5

Various structural and non-structural genes encoding for proteins of the 2019-nCoV and the genome nucleotide position. ORF = open reading frames, S = structural protein, N = nucleocapsid. Modified from original Fig. 1 showing genome characterization of 2019-nCoV WIV04 and the similarity plot based on the full length genome sequence of the isolate with sequences of other coronaviruses like the SARS-CoVBJ01, batSARSr-CoV and 3 other bat coronaviruses (batSARSr-CoV W1V1, bat coronavirus RaTG13 & ZC45). Nature, Vol. 579,12 March 2020.