Etiology of COVID-19

 Etiology means the causation of a disease, where one or more factors are combined to cause the illness. In the case of COVID-19, etiological studies are helpful to determine the factors causing illness and they are required to pave the way for advanced treatment options. The main etiology for COVID-19 is immunopathogenesis which can be explained in terms of different stages of infection. This book chapter summarizes the etiology of COVID-19, different stages of COVID-19 infection, and the innate and adaptive immune response of the host to 2019-nCoV. In the early stages of infection, mild viral infection targets the nasal epithelial cells, followed by bronchial epithelial cells, and alveolar pneumocytes. In the moderate type of infection, Type-II pneumocytes are induced by the associated viral pyroptosis that leads to the triggering of IL-1β inflammatory signals, which is regarded as a localized inflammatory response. In the severe type of infection, exuberant cytokine storm syndrome (CSS) causes inflammation of the lungs, enhanced vascular hyper-permeability, and diffuse alveolar damage (DAD). As a result of the above effects, the severe stage of infection is characterized by pneumonia, ARDS (acute respiratory distress syndrome), and ALI. The infection causes CSS hyper-inflammation which additionally causes SIRS (Systemic inflammatory response syndrome). This SIRS finally leads to septic shock and multiple organ damage. Organ dysfunction for the liver, heart, and kidney is another problem for patients. 

Keywords: 2019-nCoV, ARDS, COVID-19 biomarkers, CSS (Cytokine storm Syndrome), Pneumonia, Pulmonary phase, Pyroptosis, Stages of COVID-19, SIRS