More Equine Piroplasmosis Cases Reported

Animal health authorities have discovered more cases of equine piroplasmosis, including 13 positive horses tested as part of a routine racetrack screening program in New Mexico, and one horse in Texas that was a cohort of a positive trace-out from an ongoing investigation.

The information was included in a Jan. 25 report issued to the World Organization for Animal Health (Office International des Epizooties, or OIE) by John Clifford, DVM, deputy administrator of the USDA's Animal and Plant Health Inspection Service. See the report.

Preliminary results of the New Mexico investigation indicate that transmission of the organism might have resulted from management practices (use of shared needles or substances between horses) rather than by a tick vector, the OIE report noted. The source of this infection is unknown. More than 3,000 New Mexico horses have been tested via the screening program. The New Mexico Livestock Board euthanized five of the positive horses, while the others remain under quarantine.


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These horses were not epidemiologically linked to the Texas outbreak, which now includes 364 positive horses in 12 states. More than 1,600 horses have been tested for equine piroplasmosis as part of this investigation, including 600 cohorts of positive horses outside the index ranch.

One cohort in Galveston County, Texas, tested positive. This animal is under quarantine.

Equine piroplasmosis is caused by blood-borne parasites Theileria equi or Babesia caballi, which can be spread by some species of ticks, the use of contaminated needles, and possibly through blood-contaminated semen of infected stallions. The disease was officially eradicated from the United States in 1988; officials have screened all imported horses for piroplasmosis for nearly 30 years.

Clinical signs of equine piroplasmosis can include a host of nonspecific problems, such as fever or anemia, and some infected horses might appear healthy. Blood tests are needed to diagnosis the disease. The only treatment is a potent type of chemotherapy that can have serious side effects in some horses.

As a result of the current investigation, Canada and several U.S. states have restricted the importation of horses from Texas. Horse owners and veterinarians shipping horses are urged to check with animal health officials in your state of destination to ensure the animals have met all entry requirements.

More information on equine piroplasmosis from the USDA Animal and Plant Health Inspection Service:

About the Author

Erin Ryder

Erin Ryder is a former news editor of The Horse: Your Guide To Equine Health Care.

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