In early December, the Colorado Department of Agriculture received notification from the CSU Veterinary Diagnostic Laboratory of a presumptive positive Equine Infectious Anemia (EIA) horse in Adams County. Confirmatory testing was completed at the USDA’s National Veterinary Services Laboratory (NVSL) in Ames, Iowa, December 23, 2025, confirming this horse positive for both EIA and Piroplasmosis. The initial positive was found during routine testing for movement, which highlights the importance of Coggins tests for movement requirements. 

The premises has been placed under quarantine, including the positive horse and 13 cohorts. The initial positive horse was euthanized. Additional tracing and testing of exposed horses has been initiated. Preliminary testing has identified four cohort horses with presumptive positive results for EIA, piroplasmosis, or co-infections with both. Confirmatory testing for these horses is pending and the investigation is ongoing.  

These are part of a high-risk group of horses used in match racing, also known as unsanctioned or bushtrack racing. In discussion with the trainer, they identified the likely route of disease transmission being an IV set that was reused between horses. We have seen an increase in EIA and Piroplasmosis cases in United States bushtrack horses over the past decade, primarily due to iatrogenic transmission (e.g., reusing needles, IV sets, drug bottles, etc.).  

What can you do?

While the current risk to the general equine population in Colorado is considered low at this time, the iatrogenic transmission highlights the importance of strict disease prevention practices. This case is another sobering reminder of the potentially devastating and far-reaching consequences of failing to adhere to sanitary protocols. Earlier this year, there was a large EIA outbreak associated with iatrogenic transmission from a veterinary clinic in Texas that resulted in the death of over 20 horses.

Please take some time to review the need for sanitary practices with your staff, including the requirements of not sharing syringes, needles, tack, or other equipment between patients.  

A negative EIA test (Coggins) is required to cross state lines in the United States, along with a Certificate of Veterinary Inspection (health certificate). CDA also strongly recommends that all equestrian shows, rodeos, fairs, and other equine events require a negative EIA test for entry, even if the horses haven’t crossed state lines, to further safeguard the equine population from potential disease spread.    

Annual EIA testing is critical 

These cases emphasize the necessity of annual EIA testing and underscore the significance of providing accurate information on laboratory testing forms, including the VS Form 10-11 (Coggins form).

• When completing a VS Form 10-11, please always:
• Put the physical address of the horse in Box 7 (stable/market address)
• Include the correct owner information, including phone number, in case state or federal officials need to follow-up on positive cases
• Scan horses for a microchip and include that number on the form
• Check for a lip tattoo and include that on the form 
• Indicate a brand in the markings section if there is one

Make sure digital pictures are clear on all sides to clearly see markings and brands (no shadows or objects interfering with the view of the horse. Images should be from the tips of the ears to where the hooves touch the ground. Animals should not be wearing any blankets, boots, or tack (other than a halter)). 

More about Equine Infectious Anemia

Equine Infectious Anemia (EIA) is a viral disease spread by large biting insects or inappropriate use of needles or other equipment between susceptible equine animals such as horses, mules, and donkeys. Infected horses may not appear to have any clinical signs of the disease, although the virus can cause high fever, weakness, weight loss, an enlarged spleen, anemia, weak pulse, and even death. There is no cure for the disease, so infected animals must be quarantined for life or euthanized.

Equine Infectious Anemia is a disease for which horses must be tested annually before they can be transported across state lines. The test for EIA is commonly called a Coggins Test.  

For additional information on EIA, please visit the USDA Equine Infectious Anemia website. EIA is a disease that is reportable to the Colorado Department of Agriculture State Veterinarian’s Office. Visit the CDA website for guidance on reportable diseases. 

More about Equine Piroplasmosis

Equine Piroplasmosis is a tick-borne or blood borne protozoal disease of equids caused by one of three protozoan parasites. Theileria equi, Theileria haneyi, or Babesia caballi are endemic to parts of Africa, the Middle East, Asia, Central and South America, Mexico, the Caribbean, and Europe. The United States is considered free of the natural tick-borne transmission of the organisms, except on the islands of Puerto Rico and the U. S Virgin Islands. However, we are not free from iatrogenic transmission from inappropriate sanitation practices between horses that are imported or transported from endemic regions into the US with the disease.  

Clinical signs for EP-infected horses usually occur in the first 10-30 days and may not affect all horses equally. Clinical signs include: reduced appetite, weakness or exercise intolerance, fever, anemia, jaundice, weight loss, labored breathing, swollen abdomen, colic, or sudden death. Horses that survive the initial signs of the disease become chronic lifelong carriers and may show no further signs of disease.  

Transmission within the United States is only known to occur through iatrogenic means from reuse of needles, syringes, or intravenous tubing used between horses, blood-contamination of multidose vials, administration of contaminated blood or plasma products, or direct blood transfusion between horses. Strict sanitation and sterile technique protocols are the key to disease prevention. Historically, EP- infected animals were euthanized however there is a treatment protocol that can be administered by an accredited veterinarian under direction of State and Federal animal health officials. Horses that elect for treatment must be quarantined until they test negative for EP. If EP infections coincide with EIA infections, euthanasia is recommended.