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Equine Infectious Anemia

What is Equine Infectious Anemia?

Equine infectious anaemia (EIA) is an infectious and potentially fatal viral disease affecting the immune system of members of the Equidae family, including horses, donkeys and mules. Most EIA-infected horses show no clinical signs of disease; however, they remain carriers of the virus for life and can be a source of infection for susceptible animals. In Canada, EIA is listed as a reportable disease under the Health of Animals Regulations. Accordingly, when EIA is suspected, it must be reported to the Canadian Food Inspection Agency (CFIA).

Is EIA present in Canada?

Yes. EIA has existed in Canada since the 1800^s and is considered to be an endemic disease in the horse population. EIA has a worldwide distribution and has been diagnosed on all continents except Antarctica. The prevalence of infection varies throughout the world and depends on the density of the horse population, the proportion of carrier animals, the insect vector population, and control activities in the particular area. In 2005, the prevalence of EIA in tested horses in Canada was 0.162%.

Is there a human health risk associated with EIA?

No. EIA does not affect humans, there is no risk of disease transmission from horses to humans.

How is the disease transmitted and spread?

Transmission of EIA occurs mainly through the transfer of contaminated blood from one animal to another. Blood-sucking insects, such as horse flies, stable flies, and deer flies, are vectors in the spread of the disease. Transmission may also occur when needles, syringes, surgical instruments, or other blood-contaminated objects are used for more than one animal. EIA can also be transmitted through the semen of an infected stallion. Foals can be infected before birth.

What are the clinical signs of EIA?

An outbreak of EIA usually follows the introduction of an infected animal. The incubation period is generally two to four weeks, but may range from one week to three months.

Initially, infected horses may show signs of anorexia, depression, general weakness, and weight loss. In some cases, a loss of coordination may be the only clinical abnormality. Intermittent fever up to 41ºC, jaundice, swelling of the extremities, and small hemorrhages under the tongue and eye are other common clinical signs. Foals infected in utero are often aborted, or die within two months of birth.

Many animals show temporary recovery from the acute stage and may even appear normal for two to three weeks before relapsing with similar but less severe signs. Episodes of clinical illness are often associated with the use of steroid drugs or with periods of stress such as hard work, hot weather, racing, or pregnancy.

Animals exhibiting acute signs of the disease have a high level of EIAV in their blood, and represent an important source of infection for other animals. Although some animals appear to make a complete recovery, they remain infected and become asymptomatic carriers of EIAV. These carriers generally have a low level of virus in their blood; however, they continue to pose a risk of infection to other healthy animals.

How is EIA diagnosed?

A tentative diagnosis can be made based on clinical signs, but blood tests are necessary for a definitive diagnosis. Even carriers of the virus will yield a positive blood test. The agar-gel immunodiffusion (AGID) test, also known as the Coggins test, and the enzyme-linked immunosorbent assay (ELISA) are the most commonly used testing methods for detection of antibodies against EIA. Because EIA is a reportable disease under the Health of Animals Regulations, only CFIA veterinarians or CFIA-accredited veterinarians may request testing. Also, testing may only be performed in a CFIA laboratory or in CFIA-accredited laboratories.

Are there any treatments for EIA?

At this time there is no curative treatment for animals with EIA, nor is there a vaccine that will prevent a horse, mule or donkey from becoming infected with the EIA virus. Supportive therapy may alleviate clinical signs in individual cases, but more critically infected horses serve as a reservoir of infection for other horses.

What can horse owners do to help control this disease?

The control of EIA is based on identification and destruction or life-long quarantine of infected animals, mandatory testing of imported horses, and efforts to prevent spread of the virus by controlling insect vectors. Horse owners can take a number of precautions to reduce the risk of infection as follows:

• Use strict hygiene practices when vaccinating or collecting blood samples from horses.
• Use disposable needles and syringes, and do not use the same needle on more than one horse.
• Implement insect control measures.
• Keep stables clean. Remove manure and debris promptly and ensure that the area is well drained to inhibit insect breeding.
• Do not intermingle infected and healthy animals. Isolate all new horses until they have been tested for EIA.
• Do not breed EIA-positive horses.
• Ensure negative EIA test certification is required for horse shows, fairs, race tracks, and other places where horses are assembled.
• Abide by the national EIA control program.
• Consult your veterinarian if you suspect your horse may be infected by EIA.

What is the CFIA's national program for the control of EIA in horses?

EIA is a reportable disease under the Health of Animals Regulations. This means that all suspected cases must be reported to the CFIA and all reported suspect cases are immediately investigated by Agency inspectors.

The CFIA's national program for the control of EIA in horses includes the following:

• identification of EIA infected horses: EIA-negative certification is required for certain horse shows, sales, stables, race tracks, and other places where many horses are assembled;
• confirmation (re-testing) of positive reactors;
• quarantine of premises on which EIA-positive reactors are found;
• testing of all susceptible animals housed with the positive reactor and all horses in contact with the reactor within a 30-day period;
• destruction or permanent isolation of EIA-positive animals;
• monetary compensation for horses ordered destroyed by the CFIA;
• mandatory testing of imported horses; and,
• horses imported into Canada must test negative for EIA.

How to get more information?

Contact your Canadian Food Inspection Agency Area Office:

You can find your local Canadian Food Inspection Agency District Office on the CFIA Web site or by consulting the blue pages of your local phone directory.