Biological mechanisms of viral infection
Coronaviruses are a type of single-stranded positive-sense RNA viruses
characterized by spike-like projections on their surface (Zimmermann P
et al., 2020). Among these viruses, SARS-CoV-2, SARS-CoV, and Middle
East respiratory syndrome coronavirus (MERS-CoV) are examples of
zoonotic viruses capable of infecting humans and leading to severe
respiratory infections. However, it’s important to note that they are
primarily transmitted through animals.
ACE2 receptors are prevalent in various tissues throughout the human
body, particularly on the cells of alveolar epithelium II. The spike
proteins enveloping the coronavirus attach primarily to the ACE2
receptors located on type II alveolar cells, facilitating the injection
of the virus’s RNA into these cells. Subsequently, this RNA essentially
takes control of the cell, compelling it to produce and release numerous
copies of the virus into the alveoli. As a result of this process, the
host cell is destroyed, and fresh coronaviruses infect adjacent cells.
Importantly, this sequence of events can initially occur without the
individual exhibiting any awareness of the infection, leading to
asymptomatic cases. This mechanism is a key factor contributing to the
efficient spread of COVID-19.