Viral gastroenteritis is a common illness in humans, with high morbidity reported worldwide and substantial mortality reported in developing countries. In recent years, caliciviruses have emerged as an important cause of viral gastroenteritis in people of all age groups and the main cause of outbreaks of gastroenteritis in such institutions as nursing homes and hospitals. Numerous outbreaks of Calicivirus infection have been linked to the consumption of food prepared by infected food-handlers.
The human caliciviruses have been divided into 2 genera on the basis of genome organization, morphology, and genetic and antigenic properties. Norwalk virus is the prototype strain for the genus “Norwalk-like viruses” (NLVs). These small, round-structured viruses are most commonly found in association with illness in humans. Sapporo virus is the prototype strain for the genus “Sapporo-like viruses” (SLVs), which can infect humans as well.
The cloning and characterization of the Norwalk virus genome has allowed the development of molecular detection assays that have been applied in molecular epidemiological studies. By now, it has become apparent that the NLV genus is in fact a very diverse group of viruses and that multiple variants or genotypes cocirculate in the community. Similarly, SLVs were found to consist of a group of related viruses.
Some studies involving volunteer subjects and numerous outbreak investigations have been performed to improve understanding of the course of infection and disease in healthy adult volunteers or in outbreaks of gastroenteritis. These studies have resulted in the so-called “Kaplan criteria,” which are considered highly indicative for caliciviral gastroenteritis outbreaks: an incubation period of 15–50 h, presence of acute symptoms (including vomiting) in more than one-half of cases and/or diarrhea, average duration of symptoms of 12–60 h, a high attack rate, and stool samples that test negative for bacterial pathogens.
SLV infection was more common among children aged <1 year than it was among children aged ⩾1 year. Again, a high prevalence of antibodies against SLV in adults has been described elsewhere and SLV infections were rarely detected in people aged >12 years, which suggests the induction of protective immunity after exposure to the viruses during childhood. However, the high prevalence of SLV infection in children aged <6 months would suggest the absence of maternal antibodies.
Microbiology: Current Research