Source: Alberta Veterinary Medical Association

Equine Infectious Anemia (EIA), also known as Swamp Fever, is an infectious disease of horses, donkeys, and mules caused by a virus. Horses infected with the EIA virus carry it for life. Most infected horses show no symptoms, but they remain infectious, endangering the health of other horses. The best protection against EIA is to understand the disease and the control measures that can help keep your horses from contracting it.

Horses pastured in swampy areas where insects are abundant are at greater risk of contracting EIA. Photo: Canstock/Akarelias

What is EIA?

EIA is a viral disease that affects the horse’s immune system. The virus reproduces in the horse’s blood cells and circulates throughout the body. The horse’s immune system produces antibodies, which attack and destroy its own blood cell components. The result is anemia and organ-damaging inflammation. 

Symptoms

The clinical symptoms of EIA are variable and include fever, anorexia, depression, swelling of the underside of the belly and legs, muscle weakness and wasting, jaundice of mucous membranes, and infertility. EIA can leave a horse vulnerable to other potentially fatal diseases.

EIA has three phases:

• Acute - During this phase the virus is active, multiplying and harming the immune system. The acutely ill horse has heavy concentrations of the virus in its bloodstream.
• Chronic - The animal has high concentrations of the virus in its blood, but may alternate between remission and disease states.
• Inapparent Carrier - the horse carries the virus but shows no apparent signs of illness. Stress or disease may trigger an acute episode.

At this time, there is no treatment or cure for a horse that has contracted EIA. There is also no vaccine available to protect a horse from the EIA virus.

Transmission

EIA is a blood-borne disease transmitted mainly through the natural feeding of large biting insects, principally horseflies and deerflies. Transmission can also occur through the re-use of contaminated needles and surgical and dental instruments. Because these processes can be identified, decisions can be made regarding disease management and control.

It is important to remember the threat that an EIA-infected horse poses to the whole community. The risk may be unknown, but the consequences can be great, extending even to legal liability. Strict control measures should be followed in order to prevent the spread of this virus. All stables, farms, horse shows, racetracks, rodeos, clinics, and equine event operators are strongly encouraged to ask for and verify a current Coggins certificate for all horses entering their premises. This, along with good management practices, will help in the fight against this disease.

Farm owners should require a current negative Coggins certificate before introducing new horses to the farm, and newcomers should be quarantined and observed for signs of illness for 45 days before joining the herd. Photo: Shutterstock/Mike Russell

Risk Factors

The following factors can put horses at greater risk for contracting EIA:

• Close proximity to regions where EIA outbreaks have occurred;
• Pastures in damp, swampy areas where insects are abundant;
• Environments with a steady influx of new horses, especially if negative Coggins certificates are not required;
• Exposure to horses at shows, sales or other events where health care regulations are not enforced and a negative Coggins certificate is not required;

EIA is diagnosed by testing a horse’s blood sample. The original test was developed by Dr. Leroy Coggins in 1970 and is known as the Coggins test or the agar gel immunodiffusion (AGID) test. This test consistently and reliably detects the presence of EIA-specific antibodies in the blood. A positive test indicates a horse is infected and carries the EIA virus. Positive tests are redone several times to guarantee their accuracy. Currently an Enzyme Linked Immunoadsorbent Assay (ELISA) test is used, as it provides faster results. Positive tests are then confirmed with the older Coggins test.

Control Measures

Good management principles and control measures can reduce the risk of EIA infection in your horses. The following guidelines will help:

• Test all horses for EIA annually. Horses at greater risk should be tested every four to six months.
• Farm owners and operators should require and verify a current negative Coggins certificate before introducing any new horses to the farm or ranch.
• Quarantine new horses for 45 days and observe them for any signs of illness before introducing them to the herd. Retest them if EIA exposure is suspected.
• Horse show and event managers should require and verify negative Coggins certificates for all horses entering the premises.
• Use only one disposable needle or syringe per horse when administering vaccines or medications.
• Sterilize dental tools before using them on another horse.
• Keep all stable areas clean, dry and waste-free. Practice good pasture management techniques such as removing manure and providing adequate drainage to discourage breeding sites for pests.

Blood tests are necessary for a definitive EIA diagnosis. Photo: Shutterstock/Henk Vreiselaar

EIA Regulations

If you suspect that your horse may have contracted Equine Infectious Anemia, contact your veterinarian immediately.

EIA is a reportable disease under the Health of Animals Act. This places certain legal responsibilities on veterinarians and owners/persons with custody or control of infected animals. When a Coggins test indicates that an animal is infected, a federal veterinarian will inform the owner of the test results and the legal requirements under the Health of Animals Act. A control license will be issued on the animal. It is not permitted to move the animal anywhere without this license. Any movement of infected animals other than to slaughter is not recommended.

An owner who moves an EIA infected animal without a license is in contravention of the Health of Animals Act.

Affected animals are prohibited by law from entering community pastures, parklands, competitions, racetracks, shows, stables, or any place where horses, mules, or donkeys are assembled. Although it is recommended that an EIA-positive horse be humanely destroyed to stop further spread of the disease, the owner of an infected horse may choose to house it in permanent quarantine. However, an owner who knowingly keeps an EIA-infected horse and places other horses at risk may be held legally liable. A copy of the guidelines for permanent quarantine is available through a federal district veterinarian.

Reprinted with permission of the Alberta Veterinary Medical Association.