Equine Infectious Anemia

Courtnee Morton, DVM
By Courtnee Morton, DVM on Apr. 25, 2022
Beautiful, brown horses on the farm during the sunrise.

In This Article


What Is Equine Infectious Anemia (EIA)?

EIA is a blood-borne infection caused by a Lentivirus, a virus in the same genus as HIV that causes AIDS in humans. It is spread by horseflies or deer flies (from an infected horse to another) and can also potentially be spread from infected/uncleaned needles, tattoo equipment, and blood transfusions from untested horses.

This infection was first noted in the U.S. in the early 1900s. Case numbers were high until the 1970s, with many fatalities and humane euthanasia was required in severe cases. Now, euthanasia is very rare. Most outbreaks can be traced back to people (re-use of needles, unclean equipment, etc.), but outbreaks are still seen worldwide.

Symptoms of Equine Infectious Anemia

Clinical signs of EIA arise typically within one to four weeks after infection. There are three phases:

  • Acute: Clinical signs can range from a fever lasting a few days to small hemorrhages, weight loss, edema, weakness, and disorientation, or rarely, death.

  • Chronic: Signs include repeated fever, chronic weight loss, and anemia. This virus lives in a horse’s tissues and will always be infectious to other horses.

  • Inapparent form: There may be no clinical signs at all, but periods of stress (travel, illness, etc.) immunosuppression or the use of steroids can induce a flare-up.

How Veterinarians Diagnose Equine Infectious Anemia

Several tests help vets diagnose EIA, including:

  • Coggins testing: Consists of a thorough physical exam and extracting blood if EIA is suspected, or for routine travel. If your horse shows signs of anemia or has a fever, blood work will be done to check for decreased platelets and increased white cell counts.

  • AGID and ELISA testing:

    • AGID testing takes more than  24 hours to complete and detects antibodies to the virus. Because the virus causes lifelong infection, this is a true positive.

    • ELISA testing can be completed in less than an hour. The test is more sensitive, but less specific. Any positive results should be re-tested with an AGID.

Treatment of Equine Infectious Anemia

There is no known treatment for EIA, and an EIA-positive horse must be isolated permanently more than 200 yards away from other horses. This is to prevent a horsefly from biting an infected horse, then flying to another close by and spreading the virus. If adequate isolation is not an option, humane euthanasia is required.

Prevention of EIA in Horses

Several precautions can be taken to prevent the spread of EIA, including:

  • Requiring negative Coggins testing before purchasing a new horse

  • Only participate in events or board at barns requiring proof of a negative Coggins test

  • Fly control

  • Quarantining horses that have a fever

  • Never re-use needles, IV sets, or syringes

Equine Infectious Anemia FAQs

What happens if my horse tests positive for EIA?

Within 24 hours of a positive result, your horse will be placed in quarantine more than 200 yards from other horses until confirmation testing and classification is complete.

How contagious is equine infectious anemia?

This disease can spread through a horse population very rapidly, even if an inapparent carrier is new to the barn. Luckily, positive cases are quite rare, and most cases can be traced back to blood-contaminated materials.

Can EIA be cured?

There is no known cure for equine infectious anemia. If a patient survives an acute infection, they may progress to a chronic carrier with occasional fever flare-ups but must live in isolation.

What is a Coggins test?

A Coggins test is a screening required for interstate travel that determines if a horse is a carrier for EIA. Most shows and barns require proof of a negative Coggins test for a horse to compete or be boarded.

Featured Image: iStock.com/Dace Znotina

Courtnee Morton, DVM


Courtnee Morton, DVM


Dr. Courtnee Morton is a 2017 Ross University School of Veterinary Medicine graduate. Since graduation, she completed an equine internship...

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