Norwalk agent-like particles associated with gastroenteritis in human beings.

Currently, 6 agents of viral gastroenteritis with properties similar to the Norwalk agent have been described. These are the Hawaii, Montgomery County, W, Ditchling, and Cockle agents, as well as the Norwalk agent. These agents are 25 to 27 nm in diameter, are nonenveloped, and have a buoyant density of 1.38 to 1.40 g/cc in CsCl. Multiple antigenic types exist among these agents. These particles have been detected by immune electron microscopy in feces of acutely ill patients. None has been successfully cultivated in vitro, and suitable animal models of disease do not exist. Studies in volunteers indicate that acute infection is associated with a reversible histopathologic change in the jejunal mucosa and with transient malabsorption. Pathogenesis of these changes remains unknown. Other similar agents will likely emerge from ongoing studies.