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Calciniviral infections
Caliciviral infections in humans are among the most common causes of viral-induced vomiting and diarrhoea, with illness lasting 1-4 days. Human caliciviruses (HCV) are commonly identified in faecal specimens from patients with diarrhoea. These viruses are very widely distributed worldwide and infection is very common. The most frequent source of infection appears to be contaminated food/beverages; these may cause up to 90% of food-related gastroenteritis outbreaks. Consumption of seafood is often implicated. There is strong evidence for ocean sources (reservoirs) of the viruses. For this reason, caliciviral diseases can be difficult or impossible to contain and eradicate. Pathogenic caliciviruses can be expected to continue emerging from the sea in unexpected forms at unexpected times in unexpected places.
The family Caliciviridae is divided into five groups, tentatively designated distinct genera. Four are known human pathogens: Sapporo, Norwalk-like small round structured viruses, hepatitis E, and the marine (animal) caliciviruses, while the fifth group, which includes RHD virus, is not yet proven to be a human pathogen.

The two period 1930-1970 saw the development of understanding concerning the marine/animal group of caliciviruses which are infective across species. By 1982, 11 species of pinnipeds and cetaceans of the North Pacific Ocean and Bering Sea (monk seals, California sea lions, northern sea lions, northern elephant seals, northern fur seals, walrus, gray whales, sei whales, sperm whales, bowhead whales, and Pacific bottlenosed dolphins) were known to be susceptible to calicivirus infection, as was an ocean fish, the opaleye perch [Girella nigricans]. Furthermore, in many instances, the virus had crossed the intertidal zone to infect terrestrial species.

On the basis of these data and the established ocean ranges of known calicivirus host species, the shores of Mexico, the USA, Canada, Russia, Korea, Japan, China, and perhaps others bordering the North Pacific Ocean had been regularly exposed to large numbers of marine caliciviruses. By this time, antibodies to two of the viral serotypes were reported in human patients in the USA. Cumulatively, these findings lead to the conclusion that fish and perhaps other ocean products provide a vehicle for transmission of these marine caliciviruses to terrestrial animals. The magnitude of potential exposure to marine caliciviruses from the sea is substantial. Marine caliciviruses remain viable more than 14 days in seawater. Since 1976, viral traffic across the land/sea interface has been observed repeatedly; also clinical caliciviral disease in humans.

Many caliciviruses are catholic in their choice of hosts; one type is known naturally to occur in five genera of seals, cattle, three genera of whales, donkeys, fox, and humans - and has additional susceptible hosts - paleyefish, horses, domestic swine, and primates.

Disease conditions involving calicivirus infections include blistering of the skin (particularly on the appendages and around the mouth), pneumonia, abortion, encephalitis, myocarditis, myositis, hepatitis, diarrhoea and coagulation/haemorrhage.Caliciviruses have the inherent potential and adaptive mechanisms to successfully parasitize essentially all organ systems of the many animal species that have been examined in detail.

Caliciviral infections in humans, among the most common causes of viral-induced vomiting and diarrhoea, are caused by the Norwalk and Sapporo calciviruses and the hepatitis E agent. Human caliciviruses have been resistant to [in vitro] cultivation, and direct study of their origins and reservoirs outside infected humans or water and foods (such as shellfish contaminated with human sewage) has been difficult. Modes of transmission, other than direct faecal-oral routes, are not well understood. In contrast, animal viruses found in ocean reservoirs, which make up a second calicivirus group, can be cultivated in vitro. These viruses can emerge and infect terrestrial hosts, including humans.

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