Missouri Equine Piroplasmosis Outbreak 'Resolved' in OIE Report

A Sept. 15 report on the cases of equine piroplasmosis earlier this year in Missouri and Kansas declares the outbreak resolved. Three positive horses that were removed from quarantine remain missing. (See the report.)

In June animal health officials confirmed equine piroplasmosis in Missouri after a horse formerly stabled at the Raytown Equestrian Park was hospitalized and found to be positive for the disease, setting off a foreign animal disease investigation. The stable, home to 64 equids, was placed under quarantine on June 6.

On June 17, someone removed two bay Quarter Horses that had been confirmed positive for causative organism Theileria equi from the Raytown quarantine. As of Sept. 15, these horses have not been located. Another five positive horses there were euthanized June 18 with their owners' consent.

A June 26 World Organization for Animal Health (or OIE) statement noted a third positive horse was also illegally removed from quarantine in Kansas. A spokesman for the Animal and Plant Health Inspection Service said the Kansas horse was a gray mare that had originated from the Raytown premises.

Equine piroplasmosis is an infectious disease caused by either of two different protozoal parasites that attack the red blood cells. It is characterized by fever, anemia, weight loss, jaundice, and, in some cases, death. The case fatality rate can be up to 20% in naive horses (those which have never been exposed). The only treatment is a potent type of chemotherapy that can have serious side effects in some horses. United States officials have screened all imported horses for piroplasmosis for nearly 30 years.

The new OIE report by John Clifford, DVM, deputy administrator of the USDA's Animal and Plant Health Inspection Service, cited needle sharing resulting in the transfer of whole blood between horses as the route of transmission of the disease. Tick surveillance performed on the index premises uncovered four ticks, which were submitted to the National Veterinary Services Laboratory. The lab determined the ticks found were not competent vectors for the causative organism.

All equids remaining at and traced to the index premises have tested negative for Theileria equi.

"The investigation into the illegal removal of the horses from the index premises continues to be conducted by law enforcement agencies. Non-substantiated accounts indicate that the illegally removed horses have been illegally transported out of country," the report noted. "All epidemiological investigations of this event have been concluded and, unless new law enforcement information is uncovered, this equine piroplasmosis event is considered closed."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.