History of strain

Many viral epidemics have been reported in the last 20 years. The best known examples include the severe acute respiratory coronavirus syndrome (SARS-CoV) from 2002 to 2003, with approximately 8000 cases and 800 deaths, and H1N1 influenza, in 2009.  In 2012, around 2,500 cases and 800 deaths recorded due to Middle East RespiratorySyndrome coronavirus (MERS-CoV), which was first identified in Saudi Arabia. The novel MERS coronavirus, which was suspected of having originated in bats, was similar to other coronaviruses.  It was believed to have transferred from bats to other species prior to being transmitted to humans. Camels were also identified as a possible MERS reservoir.

The new virus was first known as 2019-nCoV. Then, it wasrenamed SARS-CoV-2, as it is very similar to the SARS-CoVs. Genetically, COVID-19 is less similar to SARS-CoV and MERS-CoV. Nucleocapsid protein (N), an envelope protein (E), and membrane protein (M) are different in terms of their arrangement among beta coronaviruses.

Anatomy (Structure of COVID and COVID-19)

The glycoprotein-studied envelope for electron microscopy has initially been classified into the Coronaviridae family based on the crown and halo-like appearance;this classification is supported by the particular chemical attributes and replication of these viruses. Coronavirus structure comprises protein-encompassing RNA, spike protein, and lipid membranes.   Similarly, there are spherical or pleomorphic enveloped particles that contain RNA, associated with the nucleoprotein containing single-stranded (positive-sense) inside a matrix protein capsid. The envelope includes projections of club-shaped glycoprotein.

Coronaviruses consist of enveloped virus particles of around 120 nm of diameter. Glycoprotein spikes in club-shaped surfaces give the viruses a crown-like or coronal appearance.  The nucleocapsid, which is a protein shell known as the capsid, is helical or tube-like and contains viral nucleic acids. A special strand of positive sensory RNA consists of the coronavirus genome.

It is assumed that Coronaviridae normally comprises two genes, Coronavirus and Torovirus, which vary in the morphology of nucleocapsid. Coronaviruses are the main agents of human, poultry, and bovine gastrointestinal disease. Amongst all known RNA viruses, coronaviruses have the largest genomes (26.4e31.7 kb). The numbers of small ORFs vary between preserved genes (ORF1ab, spike, envelope, membrane, and nucleocapsid) and, in separate sections, downstream to the nucleocapsid gene.

A specific fragment of the N-terminal inside the spike protein incorporates distinctive features of the viral genome. At least six ORFs are in the genome of a typical CoV, except for gamma coronavirus. A frameshift is included in ORF1a and ORF1b of coronavirus from which two polypeptides are formed, pp1a and pp1ab. These polypeptides are transformed into 16 nsps with a virally encoded 3CLpro-like or Main Protease (Mpro) chymotrypsin-like protease and one or two papain-like proteases. Both the structural and accessory proteins encode the CoV sgRNAs.

The majority of human coronaviruses are in one of two groups: 229E and OC43. This results in differences in both antigenic and culturing requirements. In human embryonic fibroblast cultures, 229E-like coronaviruses will typically be isolated. Oc43-like viruses in suckling mouse brains may be isolated and modified for growth. Between these two forms, there is little antigenic cross-reaction.  This triggers a similar disease and indistinguishable epidemics.