Babesiosis: Horses

(Equine Piroplasmosis)

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Babesiosis in the horse is caused by two protozoal piroplasms, Babesia equi and Babesia caballi. Competent vector-tick species include Rhipicephalus sanguineus and Dermacentor reticulatus.

Clinical Signs & Symptoms

Acute signs:

  • Pyrexia – generally mild (fever)
  • Lethargy (weakness / loss of energy)
  • Anorexia (loss of appetite leading to weight loss)
  • Depression
  • Icterus (Jaundice – yellowing of the skin and eyes that is caused by too much bilirubin in the blood)
  • Haemoglobinemia (excessive haemoglobin in the blood)
  • Haemoglobinuria (dark red haemoglobin-containing urine)
  • Pale mucous membranes
  • Tachycardia (rapid heart rate)
  • Tachypnea (rapid breathing)

Additionally, sweating, colic, lacrimation, incoordination, cardiac murmurs, and subcutaneous oedema around the head and eyelids can occur.

Subacute cases are characterised by intermittent pyrexia, anorexia, tachycardia, tachypnea, with variable degrees of icterus, haemoglobinuria, and bilirubinuria.

Chronic infections typically result in variable clinical presentations involving anorexia, lethargy, and mild anaemia. Of the two causative organisms, B. equi is considered more pathogenic. A variety of secondary complications may result from Babesiosis including acute renal failure, colic, enteritis, laminitis, pneumonia, infertility, and abortion. In cases with suspect clinical signs of Babesiosis, the following differential diagnoses should be considered: Equine Infectious Anaemia (EIA), Monocytic Ehrlichiosis, Red Maple Toxicosis, and hepatic disease.

On rare occasions, a peracute form of the disease occurs. Horses can die within 24-48 hours of the onset of clinical signs.

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Diagnostic Tests

Wright’s- or Giemsa-stained peripheral blood smear are considered diagnostic (in cases of chronic or subacute Babesiosis, it may not always be possible to visualize the organisms in blood-smear examination).
Polymerase Chain Reaction (PCR)
Indirect Fluorescent Antibody (IFA) assay

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If equine Babesiosis is diagnosed and treated early, there is an excellent chance of recovery. However, Babesia equi infections are known to be more refractory to treatment than those caused by Babesia caballi.

Imidocarb dipropionate @ 2.2mg/kg q24h for 2 doses is usually effective but for resistant infections 4mg/kg q24h for 4 doses.

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Medical Abbreviations

by mouth
every 8 hours
every 12 hours
every 24 hours

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There is currently no vaccine against Babesiosis available for horses in the UK.

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