Babesiosis (piroplasmosis)

There are a number of tick-borne diseases that can affect horses, including babesiosis. It is useful to know how to prevent infection, especially with increasing international horse movement, and the possible effects of global warming.

Babesiosis, also referred to as piroplasmosis, is a tick-borne disease that attacks the horse’s red blood cells.
The disease is currently found in:

  • Africa
  • Asia
  • The Middle East
  • Russia
  • Eastern and Southern Europe
  • Southern USA
  • Mexico
  • Cuba
  • Central and Southern America

Britain, Germany, Austria, Switzerland, Japan and New Zealand are currently free from disease.

Babesiosis is caused by the protozoan parasites Theileria equi (originally name Babesia equi ) and Babesia caballi. Infection with T. equi is usually more severe than infection with B. caballi.
The parasite is passed from tick to horse and vice versa when ticks bite and ingest the blood from an infected horse; they can then transfer the infection to uninfected horses via their secretions. There are many types of biting ticks that can act as vectors.
Babesiosis can also be transmitted from horse to horse via fresh blood and via contaminated needles, and other veterinary equipment if not sterile or disinfected between patients. However, tick infestations are the main cause of babesiosis.

Common signs of acute babesiosis include a fever, jaundice, depression, weakness, increased respiratory and pulse rate, blood in the urine, pale mucous membranes (gums), poor appetite and general malaise. Additionally, sweating, colic, excessive tear production, incoordination, diarrhoea and swelling of dependent areas may occur.
If newly born foals are affected they will be very weak at birth and listless, they may also be unable to suckle, have a fever, be anaemic and have severe jaundice.
Chronic infection may show poor appetite, lethargy and mild anaemia.
A variety of secondary complications can occur including acute kidney failure, colic, diarrhoea, laminitis, pneumonia, infertility and abortion.
On rare occasions, a peracute form of the disease occurs and horses can die within 24-48 hours of the onset of clinical signs.

Blood tests are very important in the diagnosis of babesiosis. Your vet will take a blood sample and examine it under the microscope to indentify T. equi or B. caballi within the red blood cells.
Your vet may also take a urine sample to test as well using urinalysis which will detect any blood in the urine.

Babesiosis can be successfully treated with the antibiotic drug imidocarb dipropionate – two doses are usually required in acute cases. Other drugs are also available to treat horses with babesiosis.
If babesiosis is diagnosed and treated early, there is an excellent chance of recovery. However, T. equiinfections are known to be more refractory to treatment than those caused by B. caballi.

Unfortunately there is currently no vaccine available against babesiosis.
The prevention of tick-horse contact is the main aim – in endemic areas this requires intensive management with regular application of topical agents that destroy ticks.
Other precautions include good hygiene, hygienic veterinary care and the isolation/testing of horses arriving from endemic areas before being allowed to come into contact with other horses.