Equine Infectious Anaemia
Equine infectious anaemia (EIA) is a virus disease of horses, mules and donkeys. It is caused by a retrovirus, belonging to the Lentivirus group, related to the virus that causes HIV in humans. It is a notifiable disease in the UK, signs include intermittent fever, weakness, anaemia and emaciation. In some instances it can be fatal, but more typically it becomes a chronic infection where animals become carriers that can infect other horses. EIA can be transmitted by transfer of blood by biting insects and occurs typically in low-lying swampy areas, hence its alternative name ‘swamp fever’.
Clinical outcomes of EIA infection
Animals may be acutely, subclinically or chronically infected. The incubation period is variable, ranging from a few days for acute infection to a few months for subacute.
Acute infection– rapid onset of full blown disease, signs include high fever, anaemia, swelling of the abdomen and legs. In some cases the horse may die suddenly.
Subacute infection– slow progression of disease, symptoms may include recurrent fever, weight loss, enlarged spleen, anaemia, swelling of the lower chest, abdomen and legs.
Chronic infection– horse tires easily, may have recurrent fever and anaemia. The animal may relapse to the subacute or acute form, even several years after the original infection. Chronically infected horses can apread the disease to other animals.
Control of disease
There is currently no vaccine available for EIA. Outbreaks are controlled by horse movement restriction of affected and in-contact animals. Diagnosis is based upon the Coggins test, which detects antibodies to EIA in infected horses [link to Diagnostic laboratory services]. This test is also used to screen horses before breeding or travel abroad.
The image below shows an example of the Coggins test, which is an immunodiffusion assay. Virus antigen is placed in the central well and diffuses outwards. Wells A and C contain positive sera, well B contains a negative sample. The black areas show where antibody in the positive sera have bound to virus antigen and formed a precipitate.
