The Texas Animal Health Commission (TAHC) continues to investigate the spread of equine piroplasmosis from a South Texas ranch, which was first detected in October 2009. Equine piroplasmosis is a tick-borne protozoal infection of horses. At least one species of tick, Amblyomma cajennense has proven capable of transmitting the blood parasite. This species of tick is endemic to South Texas and several other southern states.

Further research is underway to determine if there are other tick species capable of transmitting the parasite. The disease may also be spread between horses by unsafe animal husbandry practices such as sharing needles or equipment that is contaminated with blood. 

While piroplasmosis can be a fatal disease, many horses may display vague signs of illness, such as fever, inappetance or jaundice. Horse owners are advised to consult a private veterinarian to discuss tick control, management practices, or any concerns about illness. Several states have imposed interstate movement restrictions on horses from Texas, so owners and veterinarians are urged to call the state of destination before moving horses.  

"TAHC field personnel are still investigating how many animals may have been exposed or infected with this disease,” said Dr. Dee Ellis, Texas’ state veterinarian and executive director of the Texas Animal Health Commission, the state’s livestock and poultry health regulatory agency. “Twenty-two percent of the 1,728 horses that have been tested are positive,” he said.

In almost every case, the positive horses disclosed were directly traced to the index ranch or had contact with positive horses from the ranch. Dr. Ellis added that because of that fact, there does not appear to be a geographic correlation to the presence of the disease, but rather a correlation to exposure with positive horses.

“This is not a widespread South Texas outbreak,” Dr. Ellis went on to state.

The TAHC and USDA officials continue to trace, identify and test animals on a prioritized basis. The priorities include, 1) “direct traces” of horses that lived on the ranch, 2) “dangerous contacts” which are horses that visited the ranch, or whose dam was infected, and 3) “cohorts” which are horses that have lived with positive animals. At this time, horses living on premises adjacent to the index ranch are being tested on a voluntary basis only, since this does not appear to be a geographic outbreak.

In January, TAHC hosted a meeting with 32 representatives from 20 Texas equine industry groups to discuss the status of piroplasmosis in the state. Risk procedures for positive and exposed horses were discussed, and input sought on how the state should further respond in terms of surveillance, movement requirements, and identification of positive horses.