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Ask the Infectious Disease Expert

What essential protocols do veterinarians need to follow to prevent iatrogenic transmission of equine infectious anemia (EIA) and equine piroplasmosis (EP)?

By Angela Pelzel-McCluskey, DVM, MS

Equine infectious anemia (EIA) and equine piroplasmosis (EP) are not the same diseases most practitioners learned about in veterinary school. Over the past decade the epidemiology of both has shifted. EIA cases, once around 40 per year in the U.S., now routinely exceed 100 annually. Understanding where these diseases are occurring and in which horses is the first step toward preventing transmission.

A DIFFERENT DISEASE IN A DIFFERENT HORSE
Historically, EIA spread through fly-bite transmission in untested, neglected herds. That picture has changed. Since around 2016-2017, the majority of cases have involved Quarter Horse racehorses with iatrogenic, or human-caused, transmission, primarily through unsanctioned “bush track” racing, where sharing needles, syringes, IV sets, and injectables sourced from other countries is routine.

Social media has transformed bush track racing into a massive, well-networked community. The USDA has identified more than 200 bush tracks across approximately 33 states, a figure that dwarfs sanctioned Quarter Horse racing.

A second source is illegal horse movement across the southern border. EIA and EP are both endemic in Mexico, where no testing or control programs exist. Smuggled horses include Quarter Horse types tied to bush track operations, warmbloods, Andalusians, and even 4-H horses that command a premium in the United States. EP is a foreign animal disease—the U.S. mainland has been free of natural tick-borne transmission since the 1980s—making every infected import a genuine biosecurity risk.

THE CLINICAL PICTURE
Both diseases are lifelong infections. Chronically infected horses typically appear normal—racing, training, looking healthy—with mild anemia the only possible hematologic clue. Targeted diagnostic screening is the most reliable approach for at-risk animals.

Acute cases, particularly from iatrogenic exposure, can be dramatic. A contaminated needle delivers far more EIA virus than a fly bite and more EP blood parasite than a tick bite. Refractory fever, progressive thrombocytopenia, and worsening anemia are characteristic; some horses present as apparent colics. These clinical signs overlap with other conditions, which is why it’s important to test.

NON-NEGOTIABLE PROTOCOLS

• Never reuse needles, syringes, or IV sets. One per horse, no exceptions. Reusing an IV tubing set down a barn aisle is among the most efficient ways to spread EIA. Owners and trainers are common offenders, but the directive must come from the veterinarian.
• Do not double-dip into multi-dose vials. Re-entering a shared vial with a used needle or syringe can contaminate an entire supply.
• Disinfect all equipment that contacts blood. Dental floats and lip-tattooing equipment are easy to overlook.
• Use only FDA-approved biologics sourced within the United States. Products from outside the country carry contamination risk. Unlicensed practitioners bringing foreign plasma or biologics have been directly linked to U.S. infections. If you suspect abuse, report it through official channels.
• Train your staff. Under state practice acts, veterinarians are liable for their employees’ actions. Inadequate sterile technique training is not a defense.
• Know and test your high-risk horses. Current or former Quarter Horse racehorses, horses with unclear import history, and any horse that may have entered the country illegally through Mexico warrant EIA and EP tests. The assays are inexpensive relative to what is at stake. Ask clients where their horse came from and if it has been tested.

These diseases haven’t changed. What has changed is where they’re hiding and in which horses. Bringing that awareness into daily practice is how we prevent the next outbreak.

FOR MORE INFORMATION
Learn more about EIA and EP:
• USDA APHIS: Equine Infectious Anemia
• USDA APHIS: Equine Piroplasmosis

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