Covid-19: Viral Pathogenesis and The Host Immune Response.

Abstract

COVID-19, a pandemic caused by a betacoronavirus known as SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2) has recorded 18 354 342 number of cases and 696 147 deaths globally as of August 5, 2020. It was first recorded in Wuhan, China in 2019. The virus bears close resemblance to SARS-CoV-1 and MERS-CoV that have emerged and caused outbreaks of deadly human diseases. The main component of the virus responsible for the host range specific tropism and pathogenicity is the S-glycoprotein. The primary route of transmission of infection is through human to human via close contact, usually through spraying of droplets from sneeze or cough of an infected person. The incubation period for COVID-19 following viral infection is between 2 to 14 days. The target cells of SARS-CoV-2 are those cells that highly expressed ACE2 (angiotensin-converting enzyme 2). Viral receptor binds to the ACE2, to allow the virus entry into the cell via endosomal pathway. The host innate immune system detects the viral infection by using pattern recognition receptors which result in activation of downstream signalling cascade. Understanding the virulence factors contributing to pathology, host immune responses and strategies employed by the virus in bypassing host immune response is paramount in developing therapeutic options that can help to tackle the COVID-19 pandemics.