Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Equine Infectious Anemia, EIA

Synonyms: Swamp Fever, Mountain Fever, Slow Fever, Equine Malarial Fever, Coggins Disease


Equine infectious anemia (low blood cell count, low hemoglobin) is caused by a virus that is primarily transmitted by biting flies (horse and deer flies) or reused needles, but may also be spread by contaminated instruments (including dental equipment), blood transfusions or the transfer from a mare to foal in utero.

EIA is endemic in the United States, but much more common in the South. Although some infected horses do not show any signs of the disease others develop a fever, weakness, or swelling of the lower limbs or abdomen. It has a 30% mortality rate in seriously infected horses. EIA may cause abortion in pregnant mares.

DIAGNOSIS is with the well known Coggins test.

TREATMENT: There is no cure and no vaccine. Euthanasia or permanent quarantine are currently the only accepted approaches.

EIA is a reportable disease, meaning that if a horse has or is suspected of having this disease, vets are required to report it to agricultural authorities (usually the State Veterinarian). These authorities may investigate the case as part of a larger effort to monitor equine health and coordinate with other states and the USDA APHIS in preventing the spread of illness or disease on a national and international level.

my vet's role


Once a horse contracts EIA they are infected for life and must be stabled in quarantine facilities or euthanized. Often, state law requires that they be branded as EIA "reactors."

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
more observations

Questions To Ask Your Vet:
  • Should we retest my horse to confirm this diagnosis?
  • Should we test all of my other horses?
  • If I decide to quarantine my horse, what are the state requirements for transport and long-term stabling?
  • If my pregnant mare tests positive for EIA, what are the chances she passes it onto her foal?
  • When can we test for EIA in the foal?

Good facilities management to decrease the population of flies is recommended, including the use of fans, screens, fly repellant and fly masks and sheets. Keep horse in protected stalls during times of high fly activity. Have your vet perform a Coggins test on your horse at least yearly. Never reuse syringes or needles on multiple horses.

Author: Doug Thal DVM Dipl. ABVP