Equine Infectious Anaemia - Donkey

Introduction

Equine infectious anaemia is caused by the equine infectious anaemia virus (EIAV), a retrovirus of the lentivirus group. In the horse the disease is known as 'swamp fever' and was first described in France in the middle of the 19th century. Cases have been sporadically detected in several European countries.

The virus is distributed worldwide and infects all species of equidae. Large biting insects mechanically transmit disease from infected donkeys, mules or horses. The infection can also be spread by the use of contaminated needles and, to a limited extent, by direct contact between animals (DEFRA 2006).

In the horse, morbidity is variable and dependent on the strain and the quantity of virus transmitted. Infected animals may or may not show clinical signs of disease. In donkeys the virus is generally asymptomatic if they are otherwise healthy. This may be partly explained by the lower viral burden in infected donkeys compared to infected horses. However, there may be strains that are more pathogenic to donkeys (Cook, 2001). Once infected, horses may be carriers for many years. This may also be the case in donkeys.

Clinical features

Almost exclusively in horses, clinical signs include initial mild and nonspecific pyrexia. In severe acute cases death may occur. Chronic cases exhibit 'anaemia, weight loss, petechial haemorrhage and oedema. The virus may evade the detection of the immune system via ‘antigenic drift’, and multiply. Horses that survive the acute phase often experience recurrent bouts of the disease, declining in frequency until the animal becomes an unapparent carrier.

Diagnosis

• Serological testing is available using an agar gel immunodiffusion test (Coggins test). Note that antibodies are detected later in the infection in donkeys than in horses

Treatment

• If clinical signs appear, treatment is supportive and symptomatic

Control

• No vaccine is available
• Control of the potentially infective carrier animal
• Vector control
• Good hygiene and biosecurity e.g. when using veterinary instruments between equids

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

• Cook, S. J., Cook, R. F., Montelaro, R. C., and Issel, C. J. (2001). ‘Differential responses of Equus caballus and Equus asinus to infection with two pathogenic strains of equine infectious anaemia virus’. Veterinary Microbiology 79. pp 93-109.
• DEFRA (2006). ‘A Code of Practice for Equine Infectious Anaemia’. http://www.defra.gov.uk/animalh/diseases/notifiable/pdf/eia-cop0806.pdf. (curently not available but other link available is http://www.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/eia/index.htm)

EXOTIC INFECTIONS - DONKEY