The Mississippi state veterinarian confirmed a horse in Adams County, Mississippi, tested positive for equine infectious anemia (EIA) on Aug. 12. The positive horse, one of two from the same pasture that were tested, was euthanized Aug. 17. No other horses are known to have been exposed.

This case marks Mississippi’s first EIA-positive horse since December 2016.

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 an uninfected animal, often by blood-feeding insects such as horseflies. It can also be transmitted through the use of blood-contaminated instruments or needles.

A Coggins test screens horses’ blood for antibodies that are indicative of the presence of the EIA virus. Most U.S. states require horses to have proof of a negative Coggins test to travel across state lines