Equine Infectious Anemia (EIA): Symptoms, Testing, and Management

Equine infectious anemia (EIA) is a blood-borne infection caused by a Lentivirus, a virus in the same genus as human immunodeficiency virus (HIV) that causes acquired immunodeficiency syndrome (AIDS) in humans.

What Is Equine Infectious Anemia (EIA)?

Also known as swamp fever or horse malaria, equine infectious anemia was first noted in the United States in the early 1900s. Case numbers were high until the 1970s, with many fatalities. Humane euthanasia was required in severe cases.

EIA is a reportable disease, so if a horse is diagnosed with the disease, it must be reported to public health authorities.

Most outbreaks of EIA can be traced back to people (re-use of needles and using unclean equipment between horses, etc.), as well as biting insects.

Always make sure you have plenty of needles and syringes on hand. NEVER re-use needles between horses or for multiple injections.

Equine Infectious Anemia Symptoms

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

Acute Symptoms

Sudden onset of equine infectious anemia can cause the following symptoms:

• Fever

• Small hemorrhages

• Weight loss

• Edema (swelling)

• Weakness

• Disorientation

• Death

Chronic Symptoms

Equine infectious anemia can become chronic over time, with symptoms such as:

• Repeated fever
• Chronic weight loss
• Anemia

Chronic EIA 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 (lowering of the body’s defense system against illness), or the use of steroids such as dexamethasone or prednisolone can induce a flare-up.

How Is Equine Infectious Anemia Transmitted in Horses?

Equine infectious anemia is spread by horseflies or deer flies. These flies bite an infected horse and carry the virus to other horses when they bite them.

The disease can also potentially be spread from infected/uncleaned needles, tattoo equipment (such as for racehorses), and blood transfusions from untested horses.

Pregnant mares may also pass the infection to their foal through milk.

Equine Infectious Anemia Tests

For surveillance purposes, all horses must undergo Coggins testing. This test 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 blood cell counts.

In order to diagnose equine infectious anemia, two blood tests are available through 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 equine infectious anemia. An EIA-positive horse must be permanently isolated more than 200 yards away from other horses.

Isolation is required to prevent a horsefly from biting an infected horse, then flying to another horse close by and spreading the virus.

If adequate isolation is not an option, humane euthanasia is often required in order to protect other horses.

How To Prevent Equine Infectious Anemia in Horses

Currently, there’s no vaccine available for equine infectious anemia.

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 or share needles, IV sets, or syringes