Basic Virology and Pathophysiology of COVID-19

Abstract

The world welcomed the year 2020 with the spread of the novel coronavirus. The pandemic of COVID-19 has claimed numerous lives with the counts constantly rising day by day. SARS-CoV-2 is a single-stranded RNA virus containing a genome of approximately 30,000 base pairs. It belongs to the family Coronaviridae. Genomic characterization has revealed that it is a zoonotic virus that has somehow jumped to humans. SARS-CoV-2 complies with the general morphological characteristics of coronaviruses and has a diameter of about 70-90 nm. Spike, membrane, envelope, and nucleocapsid proteins comprise the main structural proteins of the virus and help in its transmission and pathogenesis. Its genome contains at least six open reading frames (ORFs) at the 5′ end which encode pp1a and pp1b proteins. These produce nonstructural proteins which are required for optimum function of the virus particle. The structural proteins are coded for by the ORFs near the 3′-end of the genome. SARS-CoV-2 displays typical viral internalization and amplification cycles inside the host cell to which it binds by the spike protein. This spike protein displays specific amino acid sequences in its receptor binding domain which enable it to form a strong bond to host receptor. Host cells produce different immune products as a reaction to SARS-CoV-2 infection. These are responsible for controlling the progress of infection. However, they can lead to acute respiratory distress and other tissue injuries if produced in uncontrolled quantities. Histopathological examinations of affected organs show cytopathic effects due to viral infection. A lot has been written on COVID-19—its typical and atypical symptoms, mode of spread, organ systems affected, and ways of prevention. However, an understanding of what the virus contains and actually looks like (structure), its classification and evolution (position on the phylogenetic tree), and the ways in which it can infect and produce disease in the host (pathophysiology) is important to develop strategies for prevention and mitigation of the ailment caused by the novel coronavirus. This chapter presents a detailed description of the basic virology and pathophysiology of SARS-CoV-2.