Novel Agents of Viral Enteritis in Humans

Considerable information has recently emerged regarding certain "groups" of novel viruses associated with gastroenteritis in humans. The viruses reviewed here are 20-35 nm in diameter and can be detected in the stools of acutely ill individuals with gastroenteritis. These viruses can be conveniently divided into four "groups": Norwalk-like agents, caliciviruses, astroviruses, and other small round viruses. The evidence for the etiologic association of these agents with gastroenteritis varies from agent to agent but is most extensive for the Norwalk-like agents, of which the Norwalk serotype is a major cause of epidemic gastroenteritis. Human caliciviruses appear to be relatively common causes of gastroenteritis in children, particularly in Japan and the United Kingdom. Astroviruses have been reported as occasional causes of gastroenteritis in children and adults in various parts of the world. The epidemiological significance of the other small round viruses is unknown. Because of the difficulty of cultivating these agents in vitro, biochemical and antigenic characterization of these agents is incomplete. An understanding of the pathogenesis of disease and of the roles of immune responses to infection is similarly at a primitive stage. The recent development of sensitive and efficient assays for detection of several of these agents and the reports that certain strains of human caliciviruses and astroviruses can be cultivated in vitro should facilitate characterization and epidemiological studies of these agents. Systematic, prospective epidemiological studies of these agents in well-defined populations of various age groups are sorely needed for definition of the relative importance of each agent in human disease. Such information is essential for the consideration of appropriate control measures.