coronavirus
Corona viruses were first discovered in the 1930s when an acute respiratory infection of domesticated chickens was shown to be caused by infectious bronchitis virus. Human corona viruses were discovered in the 1960s . Corona viruses are a group of related RNA viruses that cause diseases in mammals and birds . In humans, these viruses cause respiratory tract infections that can range from mild to lethal. Mild illnesses include some cases of the common cold (which is also caused by other viruses, predominantly rhinoviruses ), while more lethal varieties can cause SARS , MERS , and COVID-19 . Symptoms in other species vary: in chickens, they cause an upper respiratory tract disease , while in cows and pigs they cause diarrhea . There are as yet no vaccines or antiviral drugs to prevent or treat human corona virus infections. How did Covid-19 start? The disease appears to have originated from a Wuhan seafood market where wild animals, including marmots, birds