Horse Equine Infectious Anaemia (EIA): The Coggins Test

Equine infectious anaemia is a serious viral disease of horses with no vaccine or cure. The Coggins test is the cornerstone of international prevention, and understanding EIA is essential for responsible horse ownership.

Key Facts

Equine infectious anaemia (EIA) is caused by a lentivirus (family Retroviridae, related to HIV) that permanently infects equids — horses, donkeys, mules, and zebras
The virus is transmitted primarily by biting insects (horse flies, deer flies) and through blood contamination of needles, instruments, or blood products
Infected horses become lifelong carriers; there is no cure and no licensed vaccine — infected horses must be permanently quarantined or euthanised in most countries
Clinical signs range from acute severe disease (high fever, depression, rapid weight loss, oedema) to chronic wasting or inapparent carrier state
The Coggins test (agar gel immunodiffusion, AGID) detects antibodies against EIA virus; horses must test negative before interstate transport or international movement in many jurisdictions
In the United States, approximately 500–1,000 horses test EIA-positive annually; globally, prevalence varies significantly, with Brazil having particularly high rates in some regions
Once positive, regulations in the US require the horse to be permanently identified (tattooed/branded), kept in isolation from other equids, or euthanised
The disease is a major concern for equestrian sports, breeding programmes, and international horse movement, as export/import require Coggins testing

Welfare Considerations

Horses with active EIA experience significant suffering from recurrent febrile episodes, severe anaemia causing lethargy and breathlessness, oedema, and progressive wasting. The psychosocial welfare impact on permanently quarantined horses — isolated from conspecifics, often in remote conditions, for the rest of their lives — is substantial. Social isolation violates a fundamental welfare need for these highly gregarious animals. Horses that are euthanised due to EIA positive status — even if currently healthy or inapparent carriers — represent a welfare tragedy for individual animals, though this reflects the lack of treatment options and the prevention imperative. Humane euthanasia where isolation welfare cannot be guaranteed is considered the more ethical option in these cases by many equine welfare authorities.

What You Can Do

Ensure your horse has a current Coggins test result — required for travel and competition and good biosecurity practice
Use disposable needles and syringes, and never share equipment between horses
Control biting insects on your property through removal of standing water, appropriate fly control, and stabling during peak insect activity
If purchasing a horse, always request a current negative Coggins test result before completing the sale
Support research into EIA vaccine development — this would transform the welfare and management of the disease globally