Rotaviruses

Introduction

There  are 5 distinct antigenic groups of rotaviruses; A to E. A is the most commonly seen and studied and this is further subdivided to G and P types.Rotaviruses are thought to be mostly species specific, but some transmission between species occurs. Group A is present in all mammals, where as group B and C are only common in pigs.Strains are known to vary in virulence, but they are always confined to the gut.

The incubation period of the virus is around 1- 4 days and the disease is most prevalent in neonates, where is can be very severe and even fatal. The disease occurs in neonates that have had a failure of passive transfer of colostrum, as rotavirus antibodies are found in colostrum and would provide protection from the disease for around for some time (species dependent). Transmission is via the faeco-oral route and the virus is highly infectious and will spread rapidly through a group of animals. The young tend to excrete the virus clinically or sub-clinically in their faeces as passive maternal anitbodies wane.

The target tissue of the virus is the small intestine enteroycte. The villi become stunted and so difficulty to digest food will occur. The virus is confined to the gut, i.e. there is no viraemia.

Signalment

Will affect neonates of most species, but particularly pigs and calves. Rotavirus is NOT associated with diarrhoea in dogs and cats.

Clinical Signs

The characteristic clinical sign on the disease is proliferent 'white scour'. The onset of diarrhoea is acute and can in severe cases lead to sudden death. Other clinical signs include depression, dehydration and weight loss.

Diagnosis

Signalment and clinical signs are suggestive of the condition.

Care should be taken when examining faeces, as rotavirus is usually present in the faeces of clinically normal neonatal animals. ELISA and Latex agglutination tests can be performed on faecal samples. Blood tests for serology can be used to show rising antibody titres, but this is not useful as the majority of animals have high levels of rotavirus antibody from maternal antibodies (passive immunity).

Treatment and Control

There is no 'treatment' for this disease although fluids can be given to provide supportive therapy if severe dehydration is present.

Control measures include ensuring maternal antibody transfer to rotavirus has occured by the ingestion of colostrum in the first 24hours of life. This is the most important method of preventing this disease. Other control mechanisms include general hygiene strategies and management systems e.g. 'all in/ all out' systems and isolation of sick animals.

There is a dam vaccine avaliable in the UK in cattle. It is primarily used for beef suckler herds and is given pre-calving to ensure the dam has enough antibodies in her colostrum and to increase length of protection whilst the calf is suckling. It is not used in dairy herds as the calves are usually fed batch milk after 24hours. There is no vaccine in the UK for sows.

References

Brown, C.M, Bertone, J.J. (2002) The 5-Minute Veterinary Consult- Equine', Lippincott, Williams & Wilkins
Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science
Bridger, J and Russell, P (2007) Virology Study Guide, Royal Veterinary College 
Cowart, R.P. and Casteel, S.W. (2001) An Outline of Swine diseases: a handbook, Wiley-Blackwell
Divers, T.J. and Peek, S.F. (2008) Rebhun's diseases of dairy cattle, Elsevier Health Scieneces
Taylor, D.J. (2006) Pig Diseases (Eighth edition), St Edmunsdbury Press ltd