Officials Release More Details on Texas Equine Piroplasmosis

A ranch in Kleberg County, Texas, is under quarantine after a 7-year-old Quarter Horse mare became ill and tested positive for equine piroplasmosis earlier this month. An additional 31 horses on the ranch have also tested positive. An Oct. 20 report issued to the World Organization for Animal Health by John Clifford, DVM, deputy administrator of the USDA's Animal and Plant Health Inspection Service, gives new details on the situation.

The index mare was presented to a local veterinary hospital on Oct. 2, the reported noted. Veterinarians suspected a blood-borne pathogen and isolated the mare. Positive test results for equine piroplasmosis were received on Oct. 12. The following day, the Texas Animal Health Commission quarantined the ranch and tested 31 horses epidemiologically linked with the index animal for equine piroplasmosis. Investigators also collected ticks from five horses for testing and species identification.

On Oct. 19 investigators received positive test results for causative organism Theileria equi from the National Veterinary Services Laboratory on the 31 exposed horses, as well as the index case. An additional 96 horses were then tested, with results pending. Results of the tick investigation are also pending.

The report listed the origin of this infection as unknown or inconclusive.

Equine piroplasmosis is an infectious disease caused by either of two protozoal parasites that attack the red blood cells. Affected animals can exhibit fever, anemia, weight loss, jaundice, and, in some cases, clinical signs lead to death. The case fatality rate can be up to 20% in naive horses (those that have never been exposed), and some infected equine animals might exhibit few or no signs of disease.

The only treatment is a potent type of chemotherapy that can have serious side effects in some horses. The disease is spread by ticks, the use of contaminated needles, and possibly through blood-contaminated semen of infected stallions. Officials in the United States have screened all imported horses for piroplasmosis for nearly 30 years.

Equine piroplasmosis was officially eradicated from the United States in 1988. But in August 2008, Florida's Department of Agriculture and Consumer Services announced a positive animal in that state.

During the investigation, Florida officials quarantined 25 premises and tested more than 200 horses for the disease before the incident was declared resolved in February of this year. In all, 20 horses on seven premises were euthanized after they were found to be infected with one of the causative organisms.

In June of this year, Missouri animal health officials announced a case in that state, followed shortly by another epidemiologically linked case in Kansas. Another five positive horses were euthanized June 18 with their owners' consent. Three positive horses removed from quarantines associated with this incident remain missing. The investigation into this incident was declared closed in September. The final report said all evidence indicated that ticks did not play a role in the epidemiology of this event.

In July 2008 Texas State Veterinarian Bob Hillman, DVM, expressed concern about the potential for a major outbreak because fever ticks (Boophilus microplus or Rhipicephalus microplus), which are capable of carrying the protozoal parasites, seemed to be making an incursion into the state. Animal health officials had designated a preventive tick quarantine area covering more than one million acres to deter establishment of tick-borne diseases in the state.

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