Noroviruses (previously termed Norwalk and Norwalk-like viruses) are non-enveloped RNA viruses classified in the Caliciviridae family. The group is described collectively as small round structured viruses.
Pathology of illness: Noroviruses cause gastroenteritis in adults and children. The illness is relatively mild and symptoms include nausea, vomiting, diarrhoea, fever and abdominal pain with an incubation period of 1–4 days, usually followed by recovery without complications (Grohmann & Lee 2003). Onset occurs 24–48 hours after infection and the acute phase of the illness generally lasts between 1 and 2 days (ICMSF 1996). Norwalk virus causes illness by invading and damaging the gastrointestinal tract. Infection may not confer long-term immunity.
Human Norovirus may cause epidemic gastroenteritis amongst all age groups and may be the most significant cause of infectious intestinal illness. Attack rates for small round structured virus seafood-associated gastroenteritis in outbreaks are relatively high, with rates of 56 per cent to 89 per cent being reported (Kirkland et al. 1996; Linco & Grohmann 1980).
