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Also Known As

Babesiosis, Bilary Fever


Pirplasmosis is a parasitic blood disease that affects horses in many regions of the world. The disease is also known as equine piroplasmosis and bilary fever. It is transmitted by species of ticks in the genus Dermacentor, Rhipicephalus and Hyalomma.

Both species of Babesia affecting horses were introduced into the United States around 1958 with importation of horses from Cuba to Florida. Equine Babesiosis is now considered endemic in some area of the Southeastern United States.

Babesiosis in horses is similar to malaria in humans, with insects, mainly ticks, transmitting the infectious agent that attacks and destroys red blood cells. Both horses and humans develop fevers, become lethargic and lose their appetites.


  • Fever
  • Anorexia
  • Anemia
  • Pale mucous membranes
  • Depression
  • Colic symptoms
  • Cardiac murmurs
  • Edema around the head and eyelids
  • Loss of condition
  • Poor exercise tolerance

Atypical symptoms include:

  • Gastro-enteritis, bronchopneumonia, abortion


Horses become infected with the Babesia organism when they are bitten by feeding ticks that harbor the sporozoites in their salivary secretions. Ticks become carriers by taking a blood meal from an infected horse. Infected adult ticks host several successive cycles of replication of Babesia and pass it on to the horse when infected nymphal ticks inject the sporozoites into the new host during feeding.


Since the horse population in the United States is presumed to be extremely susceptible to equine babesiosis, management safeguards against the entry and dissemination of piroplasmosis is on-going.

Horses are not allowed into the United States if testing shows anti-Babesia caballie and/or anti-Babesia equi antibodies in horses presented for importation. One problem with this stance is that the majority of horses that are found to be serologically positive for one or both of these parasites are in other tests clinically normal.

Prevention of Babesiosis requires control of tick infestations and avoiding transfer of infected blood during routine surgical and medical procedures. .

Many ticks native to the United States have the ability to transmit Basias equi so the establishment of vector control is one method to prevent transmission of equine piroplasmosis. Current endeavors are underway with the goal of developing vaccines that would block transmission. This would alleviate the burden of equine piroplasmosis on the national/international movement of horses


Treatment of horses should be performed only by a licensed veterinarian. The veterinarian should consult current literature and pharmacological formularies before initiating any treatment.

If equine piroplasmosis is diagnosed and treated early, there is an excellent chance of recovery. Imidocarb is a Babesiacidal drug that is administered in two treatments at a 24 hour interval. For cases of Babesia equi that are resistant to therapy, four doses at 72 hour intervals may be necessary.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.