The Colorado Department of Agriculture’s State Veterinarian’s Office has confirmed a case of Equine Infectious Anemia (EIA) and Equine Piroplasmosis in a horse located in Adams County. The initial positive result was found on December 8 during routine testing required for animal movement, highlighting the importance of Coggins testing for transport. Confirmatory tests were completed at the USDA’s National Veterinary Services Laboratory on December 23, 2025.
Following the diagnosis, the affected premises have been placed under quarantine and the infected horse was euthanized. Ongoing investigations include tracing and testing 13 other horses that may have been exposed to EIA. So far, follow-up tests have identified four additional cohort horses with positive results: one for EIA, two for Piroplasmosis, and one with co-infections. The investigation is still underway.
Officials believe the likely cause of transmission was human-related. According to the trainer involved, an intravenous set was reused between horses. This incident is linked to animals used in unsanctioned or bushtrack racing—a practice associated with higher risks of disease spread due to unsafe practices such as reusing needles or IV equipment.
“These unfortunate cases serve as a critical reminder of the importance of routine testing and strict biosecurity protocols in our equine community,” said Dr. Maggie Baldwin, Colorado State Veterinarian. “While the risk to the general equine population remains low at this time, this human-caused transmission highlights that simple sanitary measures, such as using single-use needles and syringes, are vital to prevent the devastating spread of these diseases.”
Veterinarians are being reminded about best practices following this case and another recent outbreak connected to a Texas veterinary hospital. They are urged to review sanitary procedures with staff—specifically not sharing syringes or equipment between horses—and ensure annual EIA testing is conducted. Proper completion of official forms such as VS Form 10-11 (Coggins form) is also emphasized; veterinarians should provide accurate physical addresses, owner information including phone numbers for follow-up by authorities, microchip numbers if available, lip tattoos or brands where present, and clear digital photographs without blankets or tack.
For horse owners and event organizers in Colorado, officials note that while current risk remains low for most horses statewide, annual EIA testing is strongly recommended for all animals. To move horses across state lines within the United States requires both a negative EIA test (Coggins) and a Certificate of Veterinary Inspection (health certificate). The department also recommends that all equestrian events require proof of negative EIA tests regardless of interstate travel status.
Equine Infectious Anemia is a viral disease transmitted by large biting insects or improper use of medical equipment like needles; there is no cure—infected animals must be quarantined permanently or euthanized. Symptoms can include fever, weakness, weight loss, anemia and sometimes death.
Equine Piroplasmosis is caused by protozoa transmitted through ticks outside continental U.S., but within U.S., it spreads mainly via contaminated medical equipment among imported or transported horses. Clinical signs often appear within ten to thirty days after infection; surviving animals become lifelong carriers.
Both diseases are reportable conditions in Colorado according to state regulations.
For more information about these diseases visit the USDA Equine Disease website (https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/equine), and guidance on reportable diseases can be found at the CDA website (https://ag.colorado.gov/animals/reportable-animal-diseases).
