B207 - EQUINE BABESIOSIS

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B207 - EQUINE BABESIOSIS

Nature of the disease
Equine babesiosis (Equine piroplasmosis) is a vector born disease of horses due to two protozoans: Babesia equi (or Theileria equi) and Babesia caballi. Both parasites are transmitted by ticks. 
Classification
OIE, List B disease
Susceptible species
Equines: essentially horses but also donkeys, mules and zebra.
Distribution
Equine Babesiosis is distributed worldwide. It seems to be absent from the Pacific region where it has not been reported since 1976 (Australia).
Clinical signs 
Incubation for B. equi is 12-19 days and 10-30 days for B.caballi. Disease is usually more severe with B. equi. Symptoms vary from chronic to per acute form.
  • In the per acute form horses are found dead or moribund before apparition of premonitory signs.
  • In the acute form, clinical signs include:
    • Fever,
    • Anorexia and depression,
    • Anaemia,
    • Icterus and hemoglobinuria,
    • Colic
  • The chronic form usually appears after an acute phase, clinical signs are not specific and include:
    • Loss of condition,
    • Poor exercise tolerance
    • Slow recovery
  • Rarely atypical forms include gastro-enteritis, bronchopneumonia, abortions. 
Post-mortem findings 
  • Intravascular haemolysis, jaundice
  • Emaciation
  • Enlarged spleen and liver
  • Kidney pale or with haemorrhages
  • Oedema in lungs
Differential diagnosis 
Specimens required for diagnosis 
Blood smears can be submitted for parasitic observation but is rarely probing. Blood samples on EDTA can be submitted for transmission test.

Serological tests are more commonly used and techniques include the complement fixation (CF) test, which is the primary test used for qualifying horses for importation, the indirect fluorescent antibody (IFA) test and ELISA.

Transmission   
Equine babesiosis is transmitted by ticks where the parasite has a compulsory stage of sexual reproduction. Some of the competent vectors identified in the literature are listed below. Iatrogenic transmission by injection material is possible.

Ticks

B. caballi B. equi
Dermacentor reticulatus + +
Dermacentor marginatus + +
Dermacentor silvarium + ?
Dermacentor nitens + -
Rhipicephalus bursa + +
Rhipicephalus sanguineus + +
Rhipicephalus turanicus ? +
Rhipicephalus evertsi ? +
Hyalomma excavatum + +
Hyalomma scupense +  
Hyalomma dromedarii + +
Hyalomma plumbeum ? +
Risk of introduction 
Equine babesiosis could be introduced by importation of infected horses, in that case establishment of the disease depends on the existence of a competent host. Risk of introducing infective ticks is low, provided that insecticide treatment is required but associated danger is great.
Control / vaccines  
There is no vaccine. Treatment using imidocarb is usually efficient. 

If introduced best eradication is through slaughtering of infected animals and vector control.

References
  • BUSSIERAS J, CHERMETTE R, Protozoologie In Parasitologie Vétérinaire, Ecole Nationale Vétérinaire D'Alfort, 1992, p 108-118.
  • Equine Babesiosis, In Veterinary Medicine, Saunders, Eight ed, 1997, London p.1171-1179
  • Office International des Epizooties, 2002
  • SOULSBY EJL, Babesia of Horses In Helminths, Arthropods and Protozoa of Domesticated Animals, Lea and Febiger Inc, 7th ed, 1982, Philadelphia, p 719-723