Equine Piroplasmosis in Imported Sport Horses

Equine piroplasmosis (EP) is a disease caused by blood parasites Theileria equi or Babesia caballi. These parasites are naturally transmitted by certain species of ticks. If left untreated, horses can become chronically infected with this disease. They may show no clinical signs or vague signs such as exercise intolerance, mild weight loss, and transient fever. Infected horses can transmit EP to other horses either via ticks or by human-mediated or iatrogenic blood transmission. While the United States currently has no tick-borne transmission of EP, the disease is endemic in many other parts of the world. Horses imported into the United States must test negative for both T. equi And B. caballi prior to release from federal import quarantine.

In recent years, EP has been documented in the United States in sport horses of various breeds, including Andalusians, Lusitanos, Friesians, and Warmbloods. These EP-infected horses were either interested in or actively participated in sport horse events such as hunter/show jumpers, eventing and dressage, some at a high level. They came from EP-endemic countries but had not been legally imported into the United States. Further epidemiological investigations revealed that the EP positive horses:

• Illegally brought across the US border from Mexico,
• were known to be infected with EP in their country of origin, and
• Were moved illegally to avoid detection of disease.

US owners/buyers of these horses were often unaware of the horse’s disease status or how it had entered the country. If you own imported sport horses and were not involved in the legal importation of the horse, do not have documentation of the USDA’s EP negative tests upon import, or are unsure how your horse got into the country, you should consult your veterinarian and find out consider testing for EP. EP infected horses found in the United States are eligible to enroll in the USDA-APHIS EP treatment program. This program has been successful in permanently eradicating the infectious organism from chronically infected horses, improving the health of the affected horse and eliminating the risk of transmission to other horses.

Learn more about EP at www.aphis.usda.gov.