Epidemiology, transmission and pathogenesis of SARS-CoV-2

The severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2) has caused Coronavirus disease-2019 (COVID-19), the worst pandemic of the 21st century. Globally, millions of lives have been lost due to COVID-19. Transmission of SARS-CoV-2 occurs human-to-human through air droplets. SARS-CoV-2 is thought to originate from a bat Coronavirus, which might have reached human beings through intermediate hosts. SARS-CoV-2 causes a variable degree of illness in human beings, including patients being an asymptomatic, mild, moderate, and severe disease, which requires hospitalization. The common symptoms of COVID-19 include fever, cough, myalgia, dyspnea, sore throat, anosmia, ageusia, and diarrhea. The pathogenesis of COVID-19 involves the attachment, entry, and replication of the virus in the host cells. The gains entry into human cells through engagement of angiotensin-converting enzyme 2 receptor with its spike proteins. The overproduction of highly inflammatory cytokines results in a cytokine storm, leading to an increased risk of acute respiratory distress syndrome, coagulopathy, and multiorgan failure. This chapter provides insight into the epidemiology, transmission, and pulmonary and extrapulmonary pathogenesis of COVID-19.