Equine Infectious Anemia

Equine infectious anemia (EIA) is a viral disease of all equidae (horses, donkeys, mules and zebras).

EIA is a regulated disease in Florida and the entire United States. By law, laboratories must report positive EIA test results to state and federal animal health officials.

The EIA virus belongs to the family Retroviridae. This group of viruses includes the human immunodeficiency virus (HIV) and the immunodeficiency viruses of apes and monkeys (SIV), goats (CAEV), cats (FIV) and cattle (BIV).

EIA persists in the horse’s white blood cells, and in the plasma (noncellular portion of the blood) during febrile episodes.

The amount of virus in the infected animal’s blood varies. Stress due to racing, heavy exercise, transport or illness due to other causes may elevate the amount of virus in the blood.

EIA virus is an enveloped virus, does not persist in the environment, and is easily killed by most common disinfectants. The virus does not persist in soil or water.

The virus is viable (infective) for up to 96 hours on contaminated needles.

The virus stays viable in the mouthparts of a biting fly for less than four hours. Thus, horses in close contact with an infected horse are at risk of infection via fly bite.

Transmission

Natural transmission occurs when a deer or horsefly bites and consumes a blood meal from an infected horse and transfers the virus via its mouthparts to another horse.

Additionally, pregnant mares may pass the virus to the foal in utero or through the milk. Stallions can infect mares at breeding.

People can introduce the virus to a naïve horse through the use of infected blood or blood products, or through the use of blood-contaminated equipment such as needles, syringes, surgical instruments, dental equipment, tattooing equipment or any other equipment.

Clinical Signs

Clinical signs can vary widely. Most infected horses are asymptomatic, showing no signs of disease.

Acutely infected animals may develop a fever, go off feed or die suddenly.

A chronically infected equine may develop nonspecific signs such as weight loss, weakness, anemia and swelling of the legs, chest and abdomen.

Stress or immunosuppression can lead to recrudescence of disease or increased levels of viremia.

Diagnosis

A serologic (blood) test confirms the diagnosis of EIA.

The two most commonly used serologic tests are the agar gel immunodiffusion (AGID), commonly known as the “Coggins” test, and the enzyme-linked immunosorbent assay (ELISA).

A positive test indicates the presence of EIA specific antibodies. The ELISA test can detect antibodies earlier than the Coggins test.

As the ELISA test may produce false positive results, the confirmatory test for EIA is the AGID test.

Only USDA-approved laboratories can perform EIA testing in the United States.

Treatment

There is no known treatment for EIA. Infected horses become lifelong carriers and pose a risk of infection to other horses.

Prevention

There is no approved vaccine for EIA in the United States. In order to prevent infection, follow these guidelines:

• Practice good fly control by regular mucking of stalls, proper disposal of manure away from horse stabling areas, and use of fly sprays or natural predators to minimize fly presence.
• Use a sterile needle and syringe for all injections or treatments.
• Disinfect any surgical or dental equipment thoroughly between horses. Remove all debris and blood with soap and water before disinfection.
• Administer only commercially licensed blood products.
• Use a sterile needle each time when puncturing a multidose medication bottle. Consult a veterinarian to demonstrate how to use sterile technique when drawing up medications.
• Require proof of a recent negative Coggins test at time of purchase or for new horses entering the premises. Require an EIA test for horses that have spent time at premises where EIA-positive horses have been identified.
• Participate only in events that require evidence of a negative Coggins test for every horse entering the event to prevent disease introduction and spread.
• Separate horses with fevers, reduced feed intake and/or lethargy from other horses and contact a veterinarian.

Regulatory Considerations

A USDA-approved laboratory notifies state and federal animal health officials of an EIA-positive result.

In Florida, a Florida Department of Agriculture and Consumer Services (FDACS) Veterinary Medical Officer will locate the positive reactor animal, obtain a blood sample for confirmatory testing and quarantine the horse.

If a horse is confirmed to be positive for EIA, management options are limited to euthanasia or lifetime quarantine, with permanent isolation at a minimum of 200 yards from all other horses. Positive horses must be permanently identified (brand and microchip).

An epidemiologic investigation will be performed to determine the movement history of the infected equine and to identify other exposed horses or equids (horses, donkeys, mules and zebras).

Exposed equines will be quarantined and tested, and be subject to a retest 45 to 60 days after the removal of the EIA-positive horse. Quarantine will remain in effect until negative retest results are received.

For interstate movement, Florida requires proof of a negative Coggins test within 12 months prior to entering the state.

Suspected or confirmed cases of EIA must be reported to the State Veterinarian’s Office. To report EIA or other reportable diseases, call (850) 410-0900 from 8 a.m. to 5 p.m., Monday through Friday. For after-hours reporting, call 1-800-342-5869 or email RAD@FDACS.gov.