EQUUS ‘Farm Calls’ Podcast Episode 6: Equine Infectious Anemia (EIA)

There has been a major change in the mode of transmission for equine infectious anemia (EIA) in the last 10 years that horse owners need to know about.

Horse owners need to know about a major change in the mode of transmission for equine infectious anemia (EIA) that has occurred in the last 10 years.


EQUUS “Farm Calls” is brought to you in 2022 by Farnam—Your Partner in Horse Care.

Equine infectious anemia (EIA) is a potentially fatal blood-borne, infectious viral disease that has been recognized for centuries. Unfortunately, there has been a change in the major mode of transmission for equine infectious anemia (EIA) and a rise in case numbers over the last 10 years, noted Dr. Angela Pelzel-McCluskey, a National Equine Epidemiologist for the USDA’s Animal and Plant Health Inspection Service, Veterinary Services.

Pelzel-McCluskey currently oversees the federal response to reportable equine disease outbreaks nationwide and has been the lead epidemiologist for more than 30 large-scale state, regional and national disease outbreak responses during her combined state and federal service.

The equine infectious anemia virus creates a persistent infection in equids and is found nearly worldwide.

EIA’s prevalence began to rise in the 1930s and reached its destructive peak in the United States between the 1960s and 1970s. In 1975, 10,371 cases of EIA infection were detected in the United States; many of these cases exhibited severe clinical signs, and some resulted in death. Today, the majority of equids found with the infection are inapparent carriers, showing no outward signs of disease, usually found when testing is required for movement or congregation. 

The U.S. government has a longstanding control program against the contagious virus that causes EIA. In the 1970s, the Coggins test became available, and rules were put in place to test horses when they were moved or with the transfer of ownership. This helped identify many cases.

From the 1970s to early 2000, there was a decline in positive EIA tests. Then things changed, according to Pelzel-McCluskey.

Mexico has no testing for EIA, said Pelzel-McCluskey. There are still some horses that are imported illegally from Mexico, which creates a means of importing EIA.

The other major change was the rise in unsanctioned or “bush-track” racing of Quarter Horses and, more recently, Standardbreds, she said. That type of racing does not have any regulatory control of people or animals.

So, now topping the way EIA is transmitted in the United States is iatrogenic transmission. This usually is due to unsanctioned racehorse owners using unhygienic medical treatments. This could include shared needles or vials of medication, or even blood doping (taking blood from one horse and giving it to another to theoretically improve its oxygen-carrying capabilities).

Added to that issue is the fact that some horses move in and out between sanctioned (regulated) and unsanctioned racing, further spreading the virus that causes EIA.

And with the increased adoption of off-the-track racehorses of all breeds, EIA can travel into pleasure horse populations.

While Pelzel-McCluskey said this adoption of former racehorses is “wonderful,” she warns horse owners that if you are bringing in a new horse from a “dangerous” population (i.e., you don’t know the horse’s background, it was rescued from slaughter, or there was the possibility of it having participated in these unsanctioned events), “you need to take extra care and discuss risks with your veterinarian.”

The only options for horses that test positive for EIA in the United States are lifetime quarantine 200 yards from other horses or euthanasia.

Learn more about equine infectious anemia by listening to the podcast.

EQUUS “Farm Calls” is a production of the Equine Network LLC.




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