Earlier this month the Colorado Department of Agriculture (CDA) quarantined a Weld County facility after a horse residing there tested positive for equine infections anemia (EIA). Now, additional horses have tested positive for EIA, as well.

On May 4 the CDA’s State Veterinarian’s Office received notice of the positive test from the USDA National Veterinary Services Laboratory. The index horse was euthanized following the positive test. At the time, the CDA placed the horse’s home facility under a quarantine order restricting the movement of other horses until further testing was completed.

On May 23, the Equine Disease Communication Center shared an update from the CDA that states:

"This is a summary and clarification of horses recently diagnosed with EIA in Colorado. On May 2, 2017, nine of 18 horses at a Weld County premises were tested for EIA and piroplasmosis for entry into sanctioned racetracks. One horse tested positive for EIA and was euthanized and subsequently an additional nine cohort horses were tested. Two of these additional nine horse tested positive for EIA and were euthanized. The remaining 15 horses were quarantined at that barn for 60 days when they will be retested for EIA and Piroplasmosis.

"On May 12, 2017 nine more horses at a second premises in Weld County, that were epidemiologically linked to the original three positive EIA horses on the first premises, were tested. An additional three horses on the second premises tested positive for EIA and were euthanized. The remaining six horses on the second premises were quarantined for 60 days when they will be retested for EIA. Currently there are 15 horses quarantined at the initial premises and six horses at the second premises pending retesting for EIA."

Equine infectious anemia is a viral disease that attacks horses’ immune systems. The virus is transmitted through the exchange of body fluids from an infected to a noninfected animal, often by blood-feeding insects such as horseflies, and more rarely through the use of blood-contaminated instruments or needles.

A Coggins test screens horses’ blood for antibodies that are indicative of the presence of EIA, and most U.S. states require horses to have proof of a negative Coggins test in order to travel.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of disease. Obvious clinical signs of the disease include progressive loss of condition along with muscle weakness and poor stamina. An affected horse also could show fever, depression, and anemia.

Editor’s Note: This article was originally posted May 22 and was updated May 24 to include new information from the Equine Disease Communication Center.