The first is sporadic gastroenteritis in infants, which most frequently is caused by rotavirus. Most of these infections are caused by caliciviruses. The third is sporadic acute gastroenteritis of adults, which is most likely caused by caliciviruses, rotaviruses, astroviruses, or adenoviruses. The pathogenesis of acute viral gastroenteritis in humans is not completely understood. The most extensive studies have been done with rotavirus because these viruses, unlike caliciviruses, will infect animal models and tissue cultures.
Rotaviruses attach and enter mature enterocytes at the tips of small intestinal villi.
They cause structural changes to the small bowel mucosa, including villus shortening and mononuclear inflammatory infiltrate in the lamina propria. Morphologic abnormalities can be minimal, and recent studies demonstrate that rotavirus can be released from infected epithelial cells without destroying them. Viral attachment and entry into the epithelial cell without cell death may be enough to initiate diarrhea. The epithelial cell synthesizes and secretes numerous cytokines and chemokines, which can direct the host immune response and potentially regulate cell morphology and function. Recent studies also suggest that one of the nonstructural viral proteins may act as an enterotoxin, promoting active chloride secretion mediated through increases in intracellular calcium concentration.