Noroviruses — Challenges to Control

Acute infectious gastroenteritis is an extremely common illness, second in frequency only to acute respiratory illness among North American families. Although it had long been suspected that such illnesses were caused by viruses, it was only after clinical and laboratory studies were carried out over the past three decades that causative viruses were identified.1,2 Among the most prominent are a novel group of viruses originally referred to as Norwalk-like agents — named after Norwalk, Ohio, where an outbreak of illness was caused by the prototype agent — and now called noroviruses.

Noroviruses are small (26 to 35 nm), single-stranded RNA viruses that are nonenveloped and have icosahedral symmetry (see image).2 They are classified as a new genus in the Caliciviridae family, which also contains the genus sapovirus, another cause of gastroenteritis.3 There is no satisfactory animal model for norovirus disease, though infection of gnotobiotic piglets and nonhuman primates has been accomplished. Human noroviruses have not been cultured in vitro, although transfection with viral RNA in human embryonic kidney cells and infection of human intestinal organoid cultures have been reported. Thus, the characteristics and pathogenesis of noroviruses have been elucidated largely through studies of disease in humans and molecular analyses of virus from human stool samples.4

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