Equine Viral Arteritis - Donkey

Introduction

EVA is caused by the equine arteritis virus (EAV), an arterivirus with only one serotype. The virus occurs worldwide and the first outbreak in a horse in the UK occurred in 1993. No clinical outbreaks have occurred since, though infections are occasionally detected. It can affect horses, donkeys, mules and possibly, zebras. To date there are no recorded naturally occurring clinical cases of EVA in donkeys (McCollum, 1995) despite a seroprevalence of 30% in some areas (Paweska, 1993).

Transmission of infection can bevia infected body fluids, particularly by the respiratory route, and to a lesser extent via contaminated fomites. Venereal spread by stallions is significant and similar in the donkey and the horse. Clinically normal but persistently infected males can spread the virus during mating to susceptible sero-negative mares. This disease is accorded great significance by the UK horse industry due to the potential for abortions and consequent economic loss on stud farms.

Clinical features

The main clinical signs seen in the horse include fever, lethargy, depression, swelling of the lower legs, conjunctivitis, swelling around the eye socket, nasal discharge and ‘nettle rash’ swelling of the scrotum and mammary gland. Abortion may also occur in pregnant mares. EVA may occasionally be fatal in the horse but infection is not often apparent.

There are several different strains of the virus with variable pathogenicity. For example, one strain isolated in donkeys and mules in South Africa was shown to be poorly transmitted to horses (Paweska, 1996). Another strain, KY-84, was shown to produce fever in all donkeys tested, with depression and slight nasal and ocular discharge in some (McCollum, 1995). The South African asinine 94 strain produced fever, depression, serous discharge and sometimes mild conjunctivitis in pregnant jennies. Abortion was not noted and the virus could not be detected in the foals (Paweska, 1997).

Diagnosis

The mild clinical signs seen in donkeys can resemble many other mild pyrexic or respiratory infections. Laboratory tests are essential to confirm a diagnosis.

• Virus detection in nasopharyngeal samples, blood, semen and possibly urine
• Virus neutralisation (VN) or polymerase chain reaction (PCR) testing of the semen can be used to detect carrier stallions

Treatment

• Symptomatic
• If a stallion remains a carrier of the virus, castration may prevent venereal spread

Control

• Strong immunity is induced by natural infection or vaccination
• In the UK, the Horserace Betting Levy Board has issued Codes of Practice on EVA (HBLB 2006) detailing control strategies
• Any donkey from a potential EAV area should be tested for carrier status before entering the UK

Following the 1993 outbreak, a killed virus vaccine has become available in the UK to protect stallions from becoming EAV shedders. Presently this has no market authorisation for use in donkeys and efficacy in this species is not known.

References

• Anzuino, J. (2008) Exotic infections In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 14

• HBLB (2006). ‘Codes of Practice on contagious equine metritis (CEM), Equine viral arteritis (EVA), Equine herpesvirus (EHV). Guidelines on strangles’. Horserace Betting Levy Board, London.
• McCollum, W.H., Timoney, P.J., and Tengelsen, L.A. (1995). ‘Clinical, virological and serological responses of donkeys to intranasal inoculation with the KY-84 strain of Equine Arteritis Virus’. J. Comp. Pathol. 112(2). pp 207-211.
• Paweska, J.T. (1997). ‘Effect of the South African asinine-94 strain of equine arteritis virus (EAV) in pregnant donkeys and mares and duration of maternal immunity in foals’. Onderstepoort Journal of Veterinary Research 64(2). pp 147-152.
• Paweska, J.T., Bernard, B.J. (1993). ‘Serolgical evidence of equine arteritis virus in donkeys in South Africa’. Onderstepoort Journal of Veterinary Research 60(2). pp 155-158.
• Paweska, J.T., Aitchison, H., Chirnside, E.D., and Narnard, B.J. (1996). ‘Transmission of the South African asinine strain of equine arteritis virus (EAV) among horses and between donkeys and horses’. Journal of Veterinary Research 63 (3). pp 189-196.

EXOTIC INFECTIONS - DONKEY