A Mississippi horse was found to be carrying a rare infectious disease earlier this month and was euthanized as a result, state officials reported.

The Mississippi Board of Animal Health reported a horse in Adams County, Mississippi, tested positive for Equine Infectious Anemia (EIA) by the state veterinarian’s office on Aug. 12.

The horse was euthanized on Aug. 17 and another horse that shared a pasture with the infected horse was tested and did not have EIA.

The state veterinarian reported it was the first positive case of EIA in a horse since December 2016. In the early to mid 20th century the disease claimed thousands of horses each year. Now only a handful of horses are killed by the disease. No vaccine or cure for the disease exists.

Horses with the disease either die from it, are euthanized or spend the rest of their lives quarantined from other animals.

EIA, sometimes called swamp fever, often causes and infected horse to have a high fever. The disease is considered fatal. Scientists say the disease is often carried by biting insects such as horse flies.