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Enteric Viruses

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It’s not just Hepatitis A and Norovirus that can make you sick…

Enteric viruses other than hepatitis A virus and the noroviruses have occasionally been implicated in foodborne disease. These include rotaviruses, astroviruses, hepatitis E virus, picornaviruses, adenoviruses and parvoviruses. Most of the enteric viruses contain RNA rather than DNA, the exceptions being adenoviruses and parvoviruses. Foodborne enteric viruses are inert particles which do not replicate in food. They require human cells to multiply. Enteric viruses can pass through the gastrointestinal tract and are resistant to environmental stresses including heat and acid. Most enteric viruses are stable at pH 2-3 (so are not inactivated by stomach acid) and in the presence of lipid solvents. They resist freezing and drying. All foodborne viruses are transmitted by the faecal-oral route and are human–specific (although animal strains of the same virus may also exist).

Adenoviruses Astroviruses Hepatitis E Parvoviruses Picornaviruses Rotaviruses
These non-enveloped DNA viruses can cause a wide range of illnesses, from mild respiratory infections in children to serious multi-organ disease. Of the many types of adenovirus, only two types, 40 and 41, are generally associated with faecal–oral spread and gastroenteritis (especially in children). Most infections are subclinical or mild. The enteric adenoviruses, types 40 and 41, are difficult to grow in cell culture, whereas most other non-faecal types can be cultured. Transmission is generally via faecally–contaminated water and evidence for foodborne transmission has not been documented.
Astroviruses infect animals and humans and cause gastroenteritis. Some strains replicate in cell culture. Generally associated with infection in young children <1 year although they may also cause a mild infection in adults. Epidemiological evidence of transmission by foods is limited, but infections via contaminated shellfish and water have been reported. Infectious dose < 100 virus particles.

Survival

Astroviruses survive heating for 30 min at 50ºC.

Hepatitis E virus belongs to the calicivirus group and is non-culturable. It occurs widely in Asia, Africa and Latin America, where waterborne outbreaks are common. It has rarely been identified elsewhere. The virus infects the liver and symptoms of hepatitis are produced following a 22-60 day incubation period. The disease is self-limiting and does not progress to a carrier or chronic state. Transmission is generally via faecally–contaminated water and evidence for foodborne transmission has not been documented.
The role of parvoviruses in human gastroenteritis is uncertain, although clearly documented in many animal species. There is limited evidence of parvovirus association with foodborne disease but it has been linked with consumption of contaminated shellfish. Parvovirus was identified in all stools examined from a large UK gastroenteritis outbreak of >800 cases. This outbreak was attributed to consumption of contaminated cockles. But association is not correlation. Parvo is largely something that infects domestic pets.
This group includes poliovirus, Coxsackie B viruses and ECHO viruses, many of which are culturable. They do not cause gastroenteritis but are transmitted by the faecal-oral route and excreted in faeces. Polioviruses were the first to be recognised as foodborne. Wild strains are now rare and much of the world is polio-free. Outbreaks of foodborne illness associated with Coxsackie virus and ECHO virus have been reported.
Rotaviruses are the major cause of childhood gastroenteritis world-wide. In developing countries, deaths are common among children < 5 years. Although the disease occurs in all age groups, it is mild and usually asymptomatic in adults. Infection is generally not recognised as foodborne but outbreaks associated with food and water have been reported in a number of countries. Many rotaviruses can be grown in cell culture. Rotaviruses infect both humans and animals; some human strains are closely related to animal strains.

Infectious dose

< 100 virus particles.

Survival

Human rotavirus can survive for several weeks in river water at 20ºC and at 4ºC.

Inactivation

Heating at 50ºC for 30 min reduces infectivity by 99%, and infectivity is rapidly lost at pH levels < 3.0 and > 10.0. Normal cooking temperatures should be sufficient to inactivate rotaviruses.

Sources of infection

Contaminated water, care-givers, food handlers, general adult population.

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