Equine Infectious Anemia

Last Modified: December 10, 2025

USDA APHIS Animal Diseases

Equine infectious anemia (EIA) is a viral, and sometimes fatal, disease that only affects equids (horses, ponies, zebras, mules, and donkeys). There is no treatment. EIA can be difficult to recognize and may be confused with other diseases. It is found in nearly all countries worldwide, including the United States. It is a reportable animal disease in all States. It is not a threat to human health.

Clinical signs range from mild to severe and appear within a few weeks after infection. However, it may take 60 days or more for the horse to test positive.

Infected animals that survive the disease become virus carriers and can infect other equids for life. They must either be euthanized or permanently isolated from other equids to prevent transmission. Carriers may also experience clinical flare-ups, often following stress or strenuous work.

What to look for:

Fever
Decreased appetite
Severe anemia
Sudden death
Jaundice (yellow discoloration of mucous membranes)
Rapid breathing, rapid heart rate
Swollen limbs
Bleeding from the nose or red/purple spots on mucous membranes
Blood-stained feces

· Chronically infected horses may show no clinical signs.

How to Prevent:

Biting, blood-feeding flies, such as horseflies or deerflies, can spread the virus from one animal to another. Historically, this has been the primary way EIA has spread. Animals can also get the virus from unclean or re-used needles and syringes, blood transfusions, and contaminated instruments, such as IV sets, dental instruments, and tattoo equipment. This type of human-facilitated transmission is now the most common way EIA spreads in the United States, particularly among current or former Quarter Horse racehorses, many with ties to unsanctioned (bushtrack) racing.

To prevent the spread of this disease:

Control biting flies on your property to reduce your animal's exposure.
Never reuse needles, syringes, or IV sets.
Only use licensed and approved blood products.
Make sure blood transfusions are performed only by licensed veterinarians using blood products from donor horses that have tested negative for EIA and other blood-borne infections like equine piroplasmosis.
Test your horses, ponies, mules, and donkeys annually for EIA.
Call your veterinarian if you suspect EIA in any equid. Immediately move horses, ponies, mules, or donkeys that you think might have EIA at least 200 yards away from other equids on your property.

How it is treated

There is no treatment or vaccine. Because infected animals become lifelong carriers, they must be permanently isolated and quarantined or euthanized.