Also known as:

  • EIA
  • Swamp Fever
  • Mountain Fever
  • Slow Fever
  • Equine Malarial Fever
  • Coggins Disease

What is Equine Infectious Anemia?

Equine infectious anemia is caused by the equine infectious anemia virus (EIAV).2 EIA cannot be transmitted to humans but is very contagious among horses and other members of the Equidae family. EIA can be found all over the world, excluding Iceland, Japan and a few other countries. In August 2011, an outbreak in Arkansas resulted in the death of 40 horses.1

How is EIA transmitted?

EIA is transmitted through biting insects, especially horse flies. It can also be spread through the use of contaminated needles or surgical equipment and through blood transfusions. Additionally, studies have found the virus in milk, which suggest it can be transmitted to nursing foals.

What are the symptoms of EIA?

Symptoms can be tricky with EIA because they mimic those of other diseases, such as anthrax, influenza, and encephalitis. Most commonly seen is a high fever, decrease in appetite, depression, and, in severe cases, anemia, jaundice, tachycardia, ventral pitting edema, or blood-stained feces. However, some horses that are infected with the disease do not develop acute symptoms. In these cases, the horse appears healthy but will eventually show signs of illness during work or stressful situations. They may also have swelling under their chest and lower legs and develop a fever on occasion. 

How do I know if my horse has EIA?

The most common way to test for EIA is the Coggins test, developed by Dr. Leroy Coggins in the early 1970s. Ordinarily, your horse will need to obtain a negative Coggins to be able to show, travel across state lines, or be sold.

There are different types of Coggins tests, such as the enzyme-linked immunosorbent assays (ELISAs) and the agar gel immunodiffusion (AGID). The ELISAs can detect the virus earlier than the AGID but can also produce false positives, which later have to be confirmed or denied by the AGID test. ELISAs are generally only used in auctions or other circumstances where a speedy result is necessary. Specific guidelines vary by state but the AGID is the most universally accepted test for transport of a horse. Results from an AGID test usually take about 24 hours. 

What is the prognosis for a horse diagnosed with EIA?

Unfortunately, there is no cure or vaccine for EIA. Therefore, once a horse is diagnosed, they must be quarantined and all other horses on the premises tested. About five percent of horses with EIA that develop acute clinical symptoms die within two to three weeks2. In horses that survive the initial phase of EIA, the symptoms seem to disappear, but they are still infected and become carriers of the disease. The symptoms may recur under stress or working conditions. The infected horses must remain quarantined for the duration of their lives, approximately 200 yards from other horses. In certain circumstances, the horse may need to be euthanized. 

What are the current recommendations to prevent against the spread of EIA?

  • Use disposable needles for the treatment and vaccination of horses
  • Never use one needle on multiple horses
  • Test horses regularly
  • Quarantine new horses for at least 30 days and until a negative Coggins is reported
  • Use insect repellant and insect control on your property


1Lenz, Dr. Thomas R. "EIA." American Quarter Horse Journal. (2011): 10. Print.
2Spickler, Anna Rovid. "Equine Infectious Anemia." "11 Aug 2009 (Last Updated)." At

Equine Infectious Anemia