Infectionwith these viruses affects the intestine and is common cause of gastrointestinalillness. Different strains of Norwalk-like viruses circulate in the community at any one time and have been named after the place where they were first detected. NLV are not sensitive by mild detergents, or di-ethyl ether, or chloroform. Exposure is by contact with infected individuals or faecally-contaminatedwater or other materials. Environmental contamination as a result of uncontrollable diarrhoea and projectilevomiting may lead to a high proportion of secondary cases.
Cooked shellfish are less of a hazard.
There are no animal models nor can they be grown incellculture. Inpractice this usually means a faecal specimen must be taken within48 hours of the onset of symptoms. This method of detection is not practical for environ- mental samples. The PCR method has been developed for clinical material and is only now being adapted for use on water andassociated material. Seeding experiments using PCR as the detection method have successfully recovered Norwalk-like virusesfrom shellfish, and recently batches implicated in transmissionof disease have been found to contain viruses.