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.