Disease Du Jour: EIA and Piroplasmosis

The U.S. horse population is at risk from EIA and piroplasmosis from a rising number of illegally imported horses through Mexico.
East Asian Longhorn Tick
The U.S. horse population is at risk from EIA and piroplasmosis from a rising number of illegally imported horses through Mexico. Image of Eastern Asian Longhorn Tick by Eric Day, Virginia Polytechnic, Bugwood.org


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In this episode of the Disease Du Jour podcast, we talk about illegal racing and illegally imported race and other competition horses in the United States causing disease issues for the U.S. horse industry. The rise of illegally imported horses and “bush track” racing in this country will continue to cause more cases of equine infectious anemia (EIA) and piroplasmosis, both of which are highly regulated in this country.

Angela Pelzel-McCluskey, DVM, MS, is a National Equine Epidemiologist for the USDA’s Animal and Plant Health Inspection Service, Veterinary Services. She has been raising the red flag for several years over this expanding disease problem.

According to confirmed reports from the Equine Disease Communication Center, in California there have been dozens of confirmed cases of EIA this year, plus EIA cases in Arizona, Iowa, Ohio, Alberta and Saskatchewan Canada, and multiple locations in Texas.

Pelzel-McCluskey said the rise in US cases of EIA—and sometimes piroplasmosis—are directly due to horses being illegally imported and participating in illegal (mostly) “bush track’ Quarter Horse racing. She said this is a growing problem.

“There are a lot more horses crossing illegally from Mexico,” said Pelzel-McCluskey. “Those horses are coming from a lot of different countries in South American and Europe.” Countries where EIA and piroplasmosis are endemic.

However, if you think this is strictly a West Coast problem, think again.

“We have found 84 ‘bush tracks’ in 24 states,” said Pelzel-McCluskey. “We have physical addresses for them.”

And that it just the tip of the iceberg.

Plus, keep in mind, she said, that AQHA only has 40 sanctioned U.S. racetracks.

One of the issues is that these illegally-imported horses—no matter their breed or discipline—do not go through importation testing required to enter the United States. Therefore, buyers “down the road” might not even know they were illegally imported.

Many of the illegally imported racing Quarter Horses will move between sanctioned and unsanctioned tracks and events. At the unsanctioned events, there are no regulations on medications or for the health and welfare of the horses. Illegal drugs, injections and blood doping are common. That sharing of blood-tinged syringes, needles and vials is a common route of iatrogenic transmission of EIA, noted Pelzel-McCluskey.

What Veterinarians Need to Do

Because Quarter Horses often end up being sold or “rescued” from a racetrack setting, the general horse population is at risk of having these potential EIA-carrier horses move around the country in other disciplines and stables.

“You don’t want a client to end up with this disease,” said Pelzel-McCluskey. “Often new owners are ‘blind’ to what the horse did previously.”

However, it is not just illegally imported Quarter Horses that equine veterinarians need to beware of. Pelzel-McCluskey said sport horses from Europe or South America often are positive for piroplasmosis. And instead of going through the long process of treating the horses, they are smuggled illegally into the U.S. These can be warmbloods, Lusitanos or Andalusians, to name a few she said.

“They might have registration papers and a microchip, but they might not have entered the U.S. legally,” Pelzel-McCluskey stated.

There is a significant population of USEF horses with piroplasmosis, she said. Those horses can be hunter/jumpers, dressage competitors or jumpers. “It doesn’t matter what the microchip says,” stressed Pelzel-McCluskey. “The horses could have been imported illegally.”

The U.S. is considered piroplasmosis-free, which means these horses will be placed in quarantine until they are cleared, she said. “That does take time,” she said. “Sometimes 1-2 years.

“We want to keep the U.S. piro-free,” she said. “And we know the Asian Longhorn tick [already in the U.S.] can transmit piroplasmosis and be a reservoir,” she said.

EIA-positive horses must be euthanized or housed 200 yards from any other horses, said Pelzel-McCluskey. The mechanical transmission of the virus can occur by stable, horse or deer fly mouthparts that hold blood. Research has shown those flies can move up to 200 yards before the blood dries out, she explained.

Because of that 200-yard knowledge, any EIA-positive horse will cause any horse within 200 yards to be quarantined until tested negative. If a horse turns up positive during the 60-day quarantine, the clock goes back to zero and the 60-day quarantine time starts anew.

“I’m not sure veterinarians are aware of the volume of horses participating in bush tracks,” said Pelzel-McCluskey. “We think there are 70,000 horses participating.”

Those horses race a couple of years and are moved out of the system. Then other horses are illegally imported.

“There is a large volume of horses coming out of this population each year,” she said. “And these horses can serve as a reservoir for disease.”

Editor’s note: If you want to watch a television news investigation into bush track racing, check out this YouTube video.

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