Skip to main content
Animal and Plant Health Inspection Service
U.S. Department of Agriculture
USDA FAQ's and resources about coronavirus (COVID-19).  LEARN MORE

Equine Piroplasmosis

What is Equine Piroplasmosis (EP)?

Equine Piroplasmosis is a blood-borne protozoal infection of horses caused by Theileria (Babesia) equi and/or Babesia caballi. Equine Piroplasmosis is present in South and Central America, the Caribbean (including Puerto Rico), Africa, the Middle East, and Eastern and Southern Europe. Only the United States, Canada, Australia, Japan, and Iceland are not considered to be endemic areas. Mortality rates for infected horses can reach 50%. Horses infected with EP can be enrolled in a USDA-APHIS-approved EP treatment program which is frequently successful at permanently eliminating the infection. EP has not been shown to be zoonotic. EP is considered a foreign animal disease in the United States and any detection must be reported to the State Veterinarian and/or the APHIS Veterinary Services Assistant Director.

There are at least 14 tick species in the genera Dermacentor, Hyalomma, Amblyomma, and Rhipicephalus that may be potential natural vectors for spreading T. equi and B. caballi.  Ticks must feed on an EP positive horse in order to spread the organism and some tick species can serve as a reservoir transmitting the infection to future generations of ticks through its eggs.  The disease can also be spread by iatrogenic means through blood and blood-contaminated equipment.  The majority of cases found within the United States have been linked to the use of contaminated medical equipment (needles, syringes, IV sets, tattooing equipment, other medical tools) and/or blood products.  Infection may be passed from mares to foals in utero.

Clinical signs are often non-specific and can include:

  • Fever
  • Reduced/Lack of Appetite
  • Anemia (loss/destruction of red blood cells)
  • Jaundice (yellow discoloration of mucous membranes)
  • Exercise intolerance/Weakness
  • Weight Loss
  • Swollen Abdomen
  • Labored Breathing
  • Colic
  • Sudden Death
Horses found positive for Equine Piroplasmosis in the United States must be placed under quarantine and can either enroll in the USDA-APHIS-approved EP treatment program, remain under life-long quarantine, or be euthanized.  The USDA-APHIS-approved EP treatment protocol uses high doses of imidocarb dipriopionate to permanently clear the organism from the horse.  Treated horses are released from quarantine once all diagnostic tests return to a negative antibody status.  Quarantines may last for one or more years as antibody titers take time to reach negative levels. 

  • Contact your local veterinarian.
  • Only use new needles, syringes and IV or medical equipment when giving any type of injection.
  • Only use licensed US biological products.
  • Check your horses for ticks regularly and if you are in a tick infested area use tick repellant products to protect your horses.

To prevent iatrogenic spread, never reuse needles, syringes or IV sets, use only new, clean needles with injectable medicines and use only licensed and approved blood products. Blood transfusions should be performed only by licensed veterinarians using donor horses tested negative for equine piroplasmosis and other blood-borne infections like EIA.

Reduce tick exposure by keeping pastures mowed, removing brush and weeds and using topical insecticides such as pyrethroid or permethrin products.  There are no vaccines available for EP prevention.

Complementary Content