General characteristics

Although the rotavirus and the Norwalk family of viruses are the leading causes of viral gastroenteritis, a number of other viruses have been implicated in outbreaks, including astroviruses, caliciviruses, enteric adenoviruses and parvovirus. Astroviruses, caliciviruses, and the Norwalk family of viruses possess well-defined surface structures and are sometimes identified as "small round structured viruses" or SRSVs. Viruses with smooth edge and no discernible surface structure are designated "featureless viruses" or "small round viruses" (SRVs). These agents resemble enterovirus or parvovirus, and may be related to them.

Astroviruses are unclassified viruses with a five or six pointed star shape as observed on the particles under the electron microscope. At least five human serotypes have been identified in England.

Caliciviruses are classified in the familyCaliciviridae. Four serotypes have been identified in England.

Enteric adenoviruses represent serotypes 40 and 41 of the familyAdenoviridae.

Parvoviruses belong to the familyParvoviridae, the only group of animal viruses to contain linear single-stranded DNA. T The Ditchling, Wollan, Paramatta, and cockle agents are candidate parvoviruses associated with human gastroenteritis.

Disease symptoms

Common names of the illness caused by these viruses are acute nonbacterial infectious gastroenteritis and viral gastroenteritis.

Viral gastroenteritis is usually a mild illness characterized by nausea, vomiting, diarrhoea, malaise, abdominal pain, headache, and fever. The infectious dose is not known but is presumed to be low.

A mild, self limiting illness usually develops 10 to 70 hours after contaminated food or water is consumed and lasts for 2 to 9 days. The clinical features are milder but otherwise indistinguishable from rotavirus gastroenteritis. Co-infections with other enteric agents may result in more severe illness lasting a longer period of time.

Diagnosis

Specific diagnosis of the disease can be made by some laboratories possessing appropriate reagents.

Identification of the virus present in early acute stool samples is made by immune electron microscopy and various enzyme immunoassays. Confirmation often requires demonstration of seroconversion to the agent by serological tests on acute and convalescent serum pairs.

Associated foods

Viral gastroenteritis is transmitted by the fecal-oral route via person-to-person contact or ingestion of contaminated foods and water. Ill food handlers may contaminate foods that are not further cooked before consumption. Enteric adenovirus may also be transmitted by the respiratory route. Shellfish have been implicated in illness caused by a parvo-like virus.

Prevention

The disease can be prevented by proper hygiene and thorough heating (over 80°C) of the foods.

Risk populations

The target populations for astro and caliciviruses are young children and the elderly. Only young children seem to develop illness caused by the enteric adenoviruses. Infection with these viruses is widespread and seems to result in development of immunity. Parvoviruses infect all age groups and probably do not ilicit a permanent immunity.