Epidemiology Clinical Features and Geographical Distribution

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Viral gastroenteritis occurs throughout the world.

The incubation period of rotavirus gastroenteritis is 1-2 days with a sudden onset of illness with watery diar rhoea lasting 4-7 days, vomiting and rapid dehydration. The spectrum of illness ranges from mild to severe. Virtually all children become infected during the first 3-5 years of life, but severe diarrhoea and dehydration occur primarily in children under the age of 3 years.

Rotavirus is also an important cause of nosocomial gastroenteritis. Rotavirus infection in adults occurs among those caring for children with diarrhoea, in travellers and in the elderly. The virus is transmitted mainly by the faecal-oral route.

The incubation period of SRSVs ranges from 10 to 48 h; diarrhoea, vomiting or both last for 1-2 days. The illness occurs typically in older children and adults, and is uncommon in preschool children. Outbreaks occur in schools, camps and holiday centres, hospitals, cruise ships and so on, and are associated with ingestion of contaminated drinking or recreational water (swimming pools), uncooked shellfish, eggs, cold foods and salads. The faecal-oral route alone does not, however, explain the explosive outbreaks that have been documented. Very large numbers of virus particles are present in vomit and vomiting is often projectile, so aerosol transmission, particularly in enclosed spaces, is likely.

Human astrovirus infections occur in childhood, often without symptoms, and in the elderly, and occasionally as the cause of foodborne outbreaks of diarrhoea. Transmission is by the faecal-oral route, person-to-person contact and possibly fomites. The seasonal incidence is highest during the winter.

Pathology

The pathogenesis of rotavirus infection is based on increasing necrosis of the gut epithelium, leading to loss of villi, loss of digestive enzymes, reduction of absorption and increased osmotic pressure, resulting in diarrhoea. These changes are followed by increased fluid secretion. The onset of dehydration may be rapid. Pathological changes in the ileum resulting from infection with SRSVs include blunting of intestinal villi, crypt hyperplasia and cytoplasmic vacuolation and lymphocytic infiltration of the lamina propria.

Pathological changes observed in animals infected with species-specific astroviruses reveal infection of mature enterocytes at the tip of the villi of the small intestine.

Diagnosis

Specific diagnosis of viral gastroenteritis is relatively easy by electron microscopy and immune electron microscopy of faecal extracts. The principal routine techniques for rotavirus include ELISA and passive particle agglutination. Molecular techniques are also available. Enteric ad-enoviruses are detected in faecal extracts mainly by ELISA using subgroup F-specific monoclonal antibodies, and by electron microscopy and immune electron micro scopy. Laboratory diagnosis of SRSVs and astroviruses is by electron microscopy or immune electron microscopy, ELISA and RT-PCR.

Management and Treatment

Oral rehydration with fluids containing sugar and electrolytes is most important, and in severe cases, particularly in children, rapid fluid replacement intravenously is a life-saving measure. If the ability to drink is lost, parent-eral administration of fluid is a medical emergency. Oral bismuth subsalicylate has been found to be beneficial in children with acute watery diarrhoea.

Antibiotics have no place in the treatment of viral gastroenteritis and specific antiviral therapy is not available.

In general, travellers' diarrhoea does not require intensive treatment apart from general supportive measures, but blood in the stools and persistent diarrhoea longer than a few days requires urgent medical attention and laboratory investigation.

Protective Measures and Prevention

General food and water hygiene measures and strict personal hygiene are important, as are sensible precautions with the consumption of food and water. Viruses causing gastroenteritis are highly contagious and spread can be rapid. Careful handwashing, personal hygiene, disinfection, and safe disposal of contaminated material and faeces are important. Outbreaks in hospitals, nurseries, holiday centres and cruise ships require meticulous application of these measures.

A rotavirus vaccine, a rhesus-based rotavirus vaccine-tetravelent (RRV-TV), has been licensed in the USA and elsewhere. RRV-TV is a live attenuated oral vaccine which incorporates a rhesus monkey rotavirus strain (with human serotype G3 specificity) and three singlegene human-rhesus reassortants. Immunisation early in life, which mimics the child's first natural infection, will not prevent all subsequent disease but should prevent most cases of severe rotavirus diarrhoea including hospital admission for treatment. The US Advisory Committee on Immunization Practices (1999a) recommends routine immunisation with three oral doses of RRV-TV for infants at the age of 2, 4 and 6 months. This vaccine can be administered together with DPT, Hib vaccine, oral polio vaccine, inactivated polio vaccine and hepatitis B vaccine. RRV-TV is effective but has now been withdrawn owing to a number of adverse events.

Vaccines against other viruses causing gastroenteritis are not available.

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