Abstract
Etiologic investigations of infectious diarrhea were long limited to bacteria and protozoa. The advent of electron microscopy and molecular biology showed that diarrhea could also be caused by viruses, both in humans and in other animals. In 1969, electron microcopy was used to show, for the first time, the responsibility of a virus in a case of calf diarrhea. This "reo-like virus "was subsequently identified as a rotavirus, and was shown only four years later to be responsible for severe diarrhea in young children. Noroviruses, and particularly the human virus Norwalk, were subsequently discovered, followed by coronavirus, sapovirus, pestivirus, astrovirus, enteric adenoviruses, torovirus, and picobirnavirus. Some of viruses found in animals, and particularly rotaviruses, can also infect humans. Rotaviruses have been identified in numerous animal species and are generally host-specific, but zoonotic transmission has been suggested by cross-infection (especially in experimental models), by genetic studies showing a close relationship between certain human and animal rotaviruses, and by the discovery of new animal genotypes during epidemiological surveillance of human rotaviroses. Some animal strains of norovirus, sapovirus, picobirnavirus and astrovirus are genetically related to human strains, but their human transmission has not been demonstrated.