sars-cov, mers-cov, sars-cov-2 comparison of three emerging coronaviruses

In december 2019, in wuhan, china began the outbreak of the new severe acute respiratory syndrome coronavirus-2 (sars-cov-2) epidemic. as a result of rapid spread, it turned into a pandemic announced by who on march 11, 2020. sars-cov-2 is an etiological factor of a new disease called covid-19. the virus is transmitted mainly through the droplet route. in most cases, it causes mild symptoms such as fever, dry cough, weakness, and muscle pain; less common symptoms include sore throat, runny nose, diarrhea, and chills. however, among people with impaired immunity and comorbidities, as well as among older people, it leads to lifethreatening complications in the form of acute respiratory distress syndrome (ards), sepsis, and septic shock. moreover, sars-cov-2 is the third highly pathogenic in humans and easily spreading coronavirus after the virus of a severe acute respiratory syndrome (sars) in 2002 - 2003 and virus of the middle east respiratory syndrome (mers) in 2012. this review summarizes current information on the emergence, origin, diversity, and common characteristics, as well as the epidemiology of the above three highly contagious coronaviruses.