EIA or Swamp Fever or Horsey AIDS

A disease that is incurable.  A disease for which there is no vaccine.  A lentivirus. Transferable by sharing saliva, blood products, dirty needles or surgical equipment, through mother’s milk, and via semen.  Sounds like HIV, but it isn’t.  It is Equine Infectious Anemia.  It has all the same characteristics of HIV/AIDS except it is a disease of horses and other equidae.  Like HIV/AIDS, once infected a horse is forever contagious, though at various stages of the disease the animal can be more or less contagious. Like HIV/AIDS it is a disease that attacks the immune system.

The HorseThere are commonly 3 forms of EIA.  In the acute form the concentration of the disease in the blood is very high.  The immune system of animals in the acute form is highly compromised.  Some animals may simply die while others will suffer from organ failure or be constantly fatigued and severely ill.  In the chronic form the animal may have high concentrations of the disease in its cells.  These animals may alternate between apparently healthy and very ill.  They may degrade over time, losing weight and becoming more and more sickly.  Animals in both the chronic and acute forms are all extremely contagious.  There is also a form known as unapparent carriers.  These animals are not sick.  They have a very low concentration of the disease in their cells, and have even been known to pass a Coggins test.  This form is quite possibly the most dangerous form of the disease.  The animal could pass a Coggins test today, have an increase in the concentration of the disease tomorrow and infect other animals, and be back to normal a day or two later.1

The disease is spread by infected mosquitos, horse flies and other biting or blood sucking insects.  Unlike diseases like Western Equine Encephalomyelitis or West Nile Virus, the concentration of the disease in the blood is high enough the horse can infect any blood sucking insect that bites it, making this disease even more contagious. While humans can be a conduit by which the disease can be spread, they are not susceptible to the disease.  In other words, humans can not get sick from EIA.2

Symtoms and Testing

Many shows and show venues now require any horses attending be accompanied by a certificate stating the horse is free of Swamp Fever or EIA.  The test, known as a Coggins Test must have been performed within the previous 6 months prior to a show.  Controversy exists regarding this test.  As stated above, a horse can test negative today and be contagious the next day.  Whether it is because the horse has the unapparent form, or it was just bitten after testing, or the disease hadn’t completed its incubation period a negative test can be misleading, and give a false sense of security.

Symptoms of the disease include:

  • Depression
  • Anorexia
  • decreased appetite
  • lower stamina
  • fatigue
  • fever
  • weight loss
  • rapid breathing
  • watery eye discharge
  • swelling of legs, lower abdomen and chest
  • changes in gait
  • wobbly gait
  • abortion in pregnant mares
  • yellowish mucous membranes

These symptoms alone do not mean the horse has EIA.  The veterinarian will have to do a Coggins Test to be sure.  Either way, if you suspect your horse has EIA remove it from the herd immediately.  Also remove,EIA in Alberta 2013 but not to the same pen, any animal that has been in contact with the infected horse, especially if the animal is showing any of the symptoms.  If the Coggins Test returns a positive result, all animals will have to be tested.  The first animal will be immediately and forever quarantined or humanely euthanized, as will any other animal returning a positive test.  Due to the fact the virus live in the cells of the animal, it is 100% incurable, and currently there is no vaccination in North America, though a live vaccine is being tested in the U.S..  The animal may be asymptomatic for years, but is still contagious.  The only options with EIA positive animals is euthanasia or quarantine in a netted pen, away from any other equidae.  Anyone working with the horse must wear quarantine clothing and not touch any other animal for several hours after working with the infected animal, unless they wore gloves and didn’t touch the animal with any skin.  In this situation, the most humane solution is probably humane euthanasia.3

Controls and Precautions

Good Hygiene Practices: 

  1. When in contact with strange horses, wear rubber gloves or, at the very least, wash your hands and use hand sanitizer before touching other animals.  Do not touch multiple animals with the same gloves on.
  2. When at shows, ensure the stalls are sanitary.  Wipe down all surfaces at face height with disinfectant before putting your horse in the stall.
  3. Do not touch your face to another animal and then touch your horse’s face.
  4. Never reuse needles to draw blood or vaccinate multiple horses.  This would include something as innocuous as glucosamine injections reusing syringes.  When administering intramuscular injections you have to draw back to check for blood.  If there was any, residue will remain in the syringe.  I will reuse a syringe, but only for the same horse.
  5. Do not allow your horse to make face to face contact with horses at shows, trail rides etc etc etc
  6. Do not allow people to touch your horse’s face unless they can wash their hands or utilize antibacterial hand sanitizer first.


  1. New horses arriving at your stable should be in non-contact quarantine for a minimum of three weeks.
  2. New horses should be considered infected animals.  You should not touch your established animals, or their buckets and water supplies without washing hands and changing boots after being in contact with quarantined animals
  3. Horses returning from show or competitions, trail rides etc. should be considered infected and be quarantined for 2-3 weeks, as if they were new to the stable.
  4. Sick animals should be quarantined until they can be tested by a veterinarian and declared EIA free.

Insect Protection:

  1. During seasons with high probability of fly bites, liberally spray the horses with insect repellant.
  2. Keep horses covered using fly sheets and face masks
  3. Keep grass around pastures mowed
  4. Remove sitting water (removes breeding areas)


  1. Keep visitors out of stalls and away from fields unless they have a reason to be there.
  2. Insist on hand washing for any visitors who may have been at another farm where they may have been in contact with other equidae
  3. Insist on contractors wearing boot covers and gloves, especially in the wet and hot months
  4. Insist all visitors follow the above hygiene regimen around your horses.


EIA is a reportable disease under The Health of Animals Act.  In other words, a veterinarian is required to report any infected animals to the Canadian Food Inspection Agency.  Upon notification CFIA will place an order of restricted movement on the facility.  This means no animals may leave or enter the premises.  The infected animal must be quarantined and all susceptible animals are tested.  Infected animals are ordered to be euthanized or put into permanent quarantine, where possible.  Once the other animals are declared clean the restricted movement order is lifted.4

Suggested Reading:  Current Listing of Canadian Outbreaks of EIA for 2013


  1. Horse Owners Today: Equine Infectious Anemia []
  2. Canadian Food Inspection Agency: Equine Infectious Anemia []
  3. Wikipedia: Equine Infectious Anemia []
  4. Canadian Food Inspection Agency: Equine Infectious Anemia []


  1. […] provincial bird of Ontario.  Even in Alberta we have some nasty mosquitos.  In previous articles here, here, and here, I have discussed various equine diseases which are spread primarily by mosquitos […]