Coronaviruses were first isolated from chickens in 1937. After the discovery of Rhinoviruses in the 1950's, ~50% of colds still could not be ascribed to known agents. In 1965, Tyrrell and Bynoe used cultures of human ciliated embryonal trachea to propagate the first human coronavirus (HCoV) in vitro. There are now approximately 15 species in this family, which infect not only man but cattle, pigs, rodents, cats, dogs and birds (some are serious veterinary pathogens, especially chickens).