ROTAVIRUS INFECTIONS

ANNA MEREDITH

Royal (Dick) School ofVeterinary Studies, University of Edinburgh, Scotland, UK

Rotaviruses are classified into a single genus within the family Reoviridai. They are 70—75 nm in diameter, icosa- hedral, triple-layered and non-enveloped, and structurally resemble a wheel, hence their name.

The rotavirus genome contains 11 segments of double-stranded RNA, which encodes six structural and six non-structural viral proteins. It is characterized by genetic variability, including point mutations, genomic reassortment and genome rearrangements, leading to considerable diversity within the genus and the continuous emergence of new strains. Seven serological groups (A-G) are recognized, and it is the group A rotaviruses (GARV) that are the most clinically significant as pathogens.

Rotaviruses are one of the most important aetiological agents of severe diarrhoeal disease in animals and humans worldwide. Rotavirus-associated enteritis is a major problem in domestic livestock, particularly in young calves, piglets and foals, but sheep and goats can also be affected. Calves are generally affected within the first 4 weeks of life, and disease involves other diverse infectious agents (bacteria, viruses and protozoa) in addition to rotavirus. Other factors such as herd management, environmental conditions, host nutrition and immune status are also important in determining the severity of disease. Rotavirus has been associated with disease in farmed deer and bison, and gastroenteritis associated with rotavirus and Helicobacter-like organisms has been reported in a 5-month-old farmed reindeer in Japan¹-¹⁴). Porcine GARV are associated with weaning and post-weaning enteritis in piglets, which can occur in both enzootic and epizootic forms in commercial piggeries. Again, co-infections with other enteric pathogens increase disease severity.

A sero- survey of wild European hogs ( Sus scrofa) in the USA failed to find evidence of rotavirus infection. Equine GARV are the major cause of diarrhoea in foals up to 3 months of age. Rotaviruses are not recognized as major pathogens of domestic carnivores, but have been reported in clinically healthy Galapagos sea lions (Zalophus californianus) and Galapagos fur seals (Arctocephalus galapagoensis) pups⁽¹⁵). A GARV is the cause of epizootic diarrhoea of infant mice (EDIM), an important disease of laboratory mice, and a high seroprevalence to rotavirus has been found in wild house mice (Mus domesticus) in Australia¹-¹⁶), in wild mice and rats on pig farms in France⁽¹⁷⁾ and in healthy wild grey squirrels (Sciurus carolinensis) in Wales, UK⁽¹⁸⁾. Recently, rotavirus has been reported in a red squirrel (Sciurus vulgaris) in Scotland, UK, in association with diarrhoea and a colorectal intussusception¹-¹⁹). Rotavirus causes enteritis in weanling domestic rabbits and antibodies to rotavirus have been demonstrated in wild cottontail rabbits (Sylvi- lagus spp.) and snowshoe hares (Lepus americanus) in Canada⁽²⁰⁾.

Rotaviruses have been reported in many avian species, including domestic poultry, guinea fowl, partridges, pheasants and pigeons¹-²¹’²²), but no reports from free-living wild bird species can be found.

Transmission is via the faeco-oral route, and rotaviruses replicate in mature villous enterocytes. The incubation period is short (usually 12—24 hours), and the epithelial cells of the duodenal villi are first to be infected. This is where replication in the cytoplasm occurs, with release of significant numbers of virions that attack the mid and distal small intestine. Rotaviruses are generally believed to be unable to multiply outside the intestinal tract or to invade deeper tissues and cause systemic disease, although this may not always be true in neonates⁽²³⁾.

As viral multiplication progresses, mature enterocytes are sloughed off and immature squamous or cuboidal cells from the crypts take over to cover the villous surface, leading to a sudden change in the ratio of absorption and secretion and thus accumulation of fluid in the intestinal lumen. Concurrent inflammatory changes in the intestinal epithelium and hypermotility lead to severe diarrhoea. Enterocytes are then regenerated and the villi recover; thus rotavirus infection is considered self-limiting, provided that the resultant dehydration and acid-base disturbance is not so significant as to cause death of very young animals. Concurrent infections may also increase disease severity.

Diagnosis is based on clinical signs and demonstration of the virus using techniques such as isolation in MA 104 cell lines, electron microscopy, electropherotyping and various serological tests.

Rotaviruses are extremely resistant in the environment and to many disinfectants.

I n domestic animals, good management and hygiene, vaccination of the dam, ensuring adequate colostrum intake in neonates and use of probiotics are all employed to control disease. Control in wild species has not been described.

Although most rotaviruses are host-restricted, interspecies transmission has been documented, and animal rotaviruses are regarded as a potential reservoir for genetic exchange with human rotaviruses and a zoonotic threat.

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Source: Gavier-Widen D., Meredith A., Duff Paul J. (eds.). Infectious Diseases of Wild Mammals and Birds in Europe. London: Wiley-Blackwell,2012. — 568 p.. 2012

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