Contribution of gut microbiota and multiple organ failure in the pathogenesis of COVID-19 infection

COVID-19, which originated in Wuhan, China, has spread rapidly all over the world. An increasing number of COVID-19 cases are caused by human-to-human transmission via respiratory droplets, coughs, and sneezes. The symptoms of COVID-19 patients are heterogeneous, ranging from mild upper respiratory symptoms (fever, languidness, unstable walking, dry cough, fatigue, and respiratory symptoms) to severe pneumonitis and even acute respiratory distress syndrome (ARDS) or death. COVID-19 invades human respiratory epithelial cells by binding with angiotensin-converting enzyme 2 (ACE2) receptors on human cell surfaces. Death in COVID-19 patients is caused by multiorgan function failure. In addition, systemic immune overactivation due to COVID-19 infection produces elevated expression of proinflammatory cytokines and chemokines, resulting in a so-called cytokine storm, a process that is an important factor in COVID-19 disease progression and multiple organ failure leading to death.