Two Dozen California Horses Test Positive For Equine Infectious Anemia (EIA)

Tulare County California map

In Tulare County, California, 24 horses tested positive for equine infectious anemia (EIA) and 11 others were exposed to the virus. iStock

On May 20, the California Department of Food and Agriculture reported that 24 horses tested positive for equine infectious anemia (EIA) in Tulare County. Eleven horses were exposed to the virus.

Angela Pelzel McCluskey, DVM, MS, is a National Equine Epidemiologist for the United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Veterinary Services. She said this outbreak dates back to Quarter Horse bush track racing. The horses were owned by several people, but were tied to the same racing team.

A 3-year-old Quarter Horse stallion from Riverside County, California was confirmed positive for EIA in early May. None of the other horses at the facility where the horse was housed at the time tested positive for EIA or piroplasmosis. But, a traceback led to the Tulare County facility where this horse originated and revealed that 24 of 35 horses at the scene tested positive for EIA. All tested negative for piroplasmosis.

“Now we know where that first horse got the infection,” Pelzel-McCluskey said.

She said the California Department of Food and Agriculture is working with owners on the disposition of those EIA-positive horses.

Pelzel-McCluskey has said for years that the illegal importation of Quarter Horse racehorses from Mexico is a source of EIA and piroplasmosis in the United States. Then, the iatrogenic transmission of these diseases (caused by human treatments such as shared needles or blood doping) spread them further in the United States.

Pelzel-McCluskey warned that some of these Quarter Horses will participate in unauthorized and sanctioned events in the United States, further spreading the disease.

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About the EIA

Equine infectious anemia is a viral disease that attacks the immune system of horses. The virus is transmitted by the exchange of bodily fluids from an infected animal to an uninfected animal, often by blood-sucking insects such as horseflies. It can also be transmitted through the use of instruments or needles contaminated with blood.

A Coggins test tests horses’ blood for antibodies that indicate the presence of the EIA virus. Most US states require horses to have proof of a negative Coggins test to cross state lines.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of the disease. Not all horses show signs of illness, but those that do may show:

  • Gradual loss of body condition;
  • Muscular weakness;
  • Poor stamina;
  • Fever;
  • The Depression; and
  • Anemia.

The EIA has no vaccine or cure. A horse diagnosed with the disease either dies, is euthanized, or must be placed in extremely strict quarantine conditions (at least 200 meters from unaffected equines) for the rest of its life.