COVID-19 : Pathogenesis & Transmission

Full-genome sequencing and phylogenic analysis indicated that the coronavirus that causes COVID-19 is a beta coronavirus in the same subgenus as the severe acute respiratory syndrome (SARS) virus (as well as several bat coronaviruses), but in a different clade. The structure of the receptor-binding gene region is very similar to that of the SARS coronavirus, and the virus has been shown to use the same receptor, the angiotensin-converting enzyme 2 (ACE2), for cell entry. The Coronavirus Study Group of the International Committee on Taxonomy of Viruses has proposed that this virus be designated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

Human coronavirus infects and kills epithelial cells of the upper respiratory tract. Virus replicates best at 33° C to 35° C; therefore, it prefers the upper respiratory tract. The envelope glycoprotein helps this virus survive the gastrointestinal tract. SARS-CoV and MERS-CoV replicate at 37° C, kill cells and initiate inflammatory responses in the lung.

The virus is most likely spread by aerosols. Most human coronaviruses cause an upper respiratory tract infection, accounting for approximately 10% to 15% of upper respiratory tract infections in humans. The disease is similar to the common cold caused by rhinoviruses but with a longer incubation period (average, 3 days). The infection may exacerbate a preexisting chronic pulmonary disease, such as asthma or bronchitis, and on rare occasions may cause pneumonia.