Rotaviruses and other diarrheal viruses.

Rotaviruses represent 80% of recognized viral etiologies and 140 million ca ses of diarrhea per year. They strike young children with similar frequency throughout the world but the mortality rate is high in developing countrie s only with some 870.000 deaths per year (WHO, 1997). Rotaviruses belong to the family of Reoviridae they are segmented bicatenary RNA viruses, which explains heir generic variability! The presence of mixed infections, the es tablishment for some rime already of a molecular epidemiology by electropho retypes. The viruses are "naked" and thus resistant to the outside environm ent; their massive elimination, 10(8) to 10(10)viral particles per gram of faeces, begins with the first day of diarrhea. They are found in used water and can also be concentrated by shellfish, the environment thus constitute s a notable reservoir for the virus. Oral-faecal transmission is facilitate d by deficient sanitary conditions. The 11 fragments of the genome each cod ify for 1 viral protein; 2 surface proteins, VP4 and VP7, bring about the f ormation of neutralizing antibodies, which are important for the protection and determination of different serotypes. A non structural protein- NSP4- would seem to intervene in the cytopathogen ic effect and may act as a veritable viral enterotoxine. Numerous animal sp ecies are infected by rotaviruses which are district from the human ones. T he pathology as it affects animals is of economic importance and of interes t as an experimental and vaccinal model. Between human and animal rotavirus es there can be genetic rematchings and the VP6 protein is an antigen commo n to the group. The description of the other viruses responsible for diarrhea has benefited from widespread use of electronic microscopes from the very first years of study of rotaviruses. These other viruses belong to 6 different types: adenovirus, calicivirus, a strovirus, Norwalk agent and related viruses, coronavirus, enterovirus. The y therefore have a structural and antigenic polymor phism but, except for t he coronavirus, they are all "naked" virions with resistance in outside env ironments and means of transmission analogous to he rotaviruses. Clinical s igns of viral gastroenterites, the age of the patient and epidemiological c ircumstances help in making an etiological diagnosis; the biological diagno sis has been simplified for the rotaviruses and the adenoviruses. Epidemics related to food or of hydric and nosocomial origin, especially those due t o the Norwalk agent, are under-declared and more frequent than those of bac terial origin. The prevention of dangers related to faeces, the improvement of sanitary conditions, health education, and better nutrition contribute to rotavirus prevention, but rotavirus diarrheas, the incidence of which is similar in developed and developing countries, would be more efficiently c ontrolled through vaccination.