Overview of viral gastroenteritis.

Diarrheal illnesses in humans have been recognized since antiquity. Such illnesses continue to take a great toll of lives, with a disproportionately high mortality in infants and young children in developing countries. Bacteriologic and parasitologic advances made during the past century led to the discovery of the etiology of some of the diarrheal illnesses, but the etiology of the major portion remained unknown. It was assumed that viruses caused most of these illnesses because: (i) bacteria were recovered from only a small proportion of episodes, and (ii) bacteria-free filtrates were found to induce gastroenteritis in adult volunteer studies. However, an etiologic agent could not be recovered despite the "golden age" of virology in the 1950's and 1960's when tissue culture technology enabled the discovery of numerous cultivatable enteric viruses, none of which emerged as an important etiologic agent of gastroenteritis. The discoveries of the Norwalk virus in 1972, and of rotaviruses in 1973, both without the benefit of in vitro tissue culture systems, ushered in a new era in the study of the etiology of viral gastroenteritis. The Norwalk virus was found to be an important cause of non-bacterial epidemic gastroenteritis in adults and older children, and rotaviruses were shown to be the single most important etiologic agents of severe diarrheal illnesses of infants and young children in both developed and developing countries. With the major advances in the study of rotaviruses, there is a high degree of optimism that in the not-too-distant future, a rotavirus vaccine will be available. In addition, the recent molecular biologic advances in the study of the Norwalk and Norwalk-like viruses, now firmly established as caliviviruses, represent a major new horizon in the study of these viruses.