July 2019

Equine Piroplasmosis (EP)

By Drs. Mike Moore, Andy Hawkins, and Laurie Beard

Recently an outbreak of equine piroplasmosis (EP) occurred in a group of racing quarter horses in Tennessee. Twenty-two horses in five separate locations tested positive for EP. The horses are all under quarantine and being treated.3

In 2017 a similar situation occurred in southwest Kansas when a routine EIA test was positive in a race horse. This led to follow up EP testing by the USDA. Seven EP positives were identified and euthanized. This incident resulted in a 33-week quarantine before all surrounding negative horses were released.4

Etiology and Incidence:

Equine piroplasmosis is caused by two blood parasites, Babesia caballi and Theileria equi.Equine piroplasmosis is currently not endemic in the United States and is considered a foreign animal disease. However, because of the increasing international nature of the horse industry, isolated outbreaks of the disease do occur. Because EP is not endemic, most U.S. horses are highly susceptible to acute forms of the disease.2


Although EP can be transmitted through infected ticks in endemic countries, it is more commonly spread through the reuse of needles and syringes, blood transfusions, or improperly cleaned and disinfected dental and surgical equipment between infected and uninfected horses. Piroplasmosis has not been shown to be zoonotic.2

Horses will not transmit the disease to other horses through casual contact. However, it is critical that horse handlers practice good biosecurity. If injections are required, use a new sterile needle and syringe on every horse.

Clinical Signs:

The incubation period is typically 5 to 30 days. Mild forms of EP can appear as weakness and lack of appetite. More severe signs include fever, anemia, weight loss, jaundiced mucous membranes, abdominal / limb edema and dyspnea.1 Horses that survive the acute phase are parasite positive for extended periods of time.


Veterinarians should contact their State Veterinarian if they are suspicious of an EP case. Blood smear and serologic testing is often performed in acute cases.

Screening for EP in normal horses is required at some racetracks and horse shows in the United States. The USDA recognizes the cELISA (competitive enzyme-linked immunosorbent assay) as the standard test for screening for EP infection.2


The treatment for EP is regulated by the USDA and the attending veterinarian must enroll in their program. High doses of imidocarb dipriopionate are injected to permanently clear the organism from the horse. Treated horses are released from quarantine once they become sero-negative. This process usually takes one to two years. For more information, please contact the USDA.


Some states and equine competitions require EP testing for entrance. If you have a client that plans to travel with their horse, check with the receiving state or competition for current import requirements.

For more information please contact KSVDL Client Care at 866-512-5650 or for more information.


  4. Hawkins, A. Personal communication.

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