Adenoviruses were discovered in 1953 and constitute a family of viruses originally isolated from the respiratory tract of man and other animals. The adenovirus family has been subdivided into two genera, mastadenovirus and aviadenovirus, referring to the virus isolated from mammalian and avian hosts, respectively. The human adenoviruses comprise 33 different serotypes. The low numbered types cause mild respiratory infections in humans, but they have not been considered to be of major clinical importance.