Theileria spp

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Giemsa-stained thin-smear blood film showing erythrocytes parasitized by Theileria annae piroplasms[1]

Theileria spp are an ampicomplexan protozoan parasite of dogs, closely related to Babesia spp.

Species which are pathogenic to dogs include:

These piroplasms are transmitted by various species of ticks including Hyalomma spp, Dermacentor spp and Rhipicephalus sanguineus[5].

Reclassification of some Babesia to Theileria spp supports the hypothesis that these new variants which were previous Babesia are characterized by high virulence for dogs and resistance to drugs used in babesiosis therapy[6].

T. annae appears to be hyperendemic in northwest Spain, thought to be transmitted by Ixodes hexagonus in north-west Spain[7].

T. annulata has been detected in asymptomatic dogs. T. equi has been detected from asymptomatic dogs and anemic dogs[8]. Co-infections with Babesia spp predominates in symptomatic dogs.

In infected dogs, symptoms of anemia and related hematological disorders predominate.

Various immune-mediated diseases have been reported associated with this parasite including thrombocytopenia[9], anemia and splenomegaly[10].

Diagnosis is based on microscopic identification of the parasite in wet blood smears and PCR speciation.

Treatment regimen involves the use of Buparvaquone. Efficacy is based on improvement of clinical signs, clearance from blood films, and absence of parasite using PCR assays.


  1. Garcia ATC (2006) Piroplasma infection in dogs in northern Spain. Vet Parasitol 138:97–102
  2. Simões PB et al (2011) Babesiosis due to the canine Babesia microti-like small piroplasm in dogs-first report from Portugal and possible vertical transmission. Parasit Vectors 4:50
  3. Criado A et al (2006) New data on epizootiology and genetics of piroplasms based on sequences of small ribosomal subunit and cytochrome b genes. Vet Parasitol 142:238–247
  4. Criado-Fornelio A et al (2003) Molecular studies on Babesia, Theileria and Hepatozoon in southern Europe. Part I. Epizootiological aspects. Vet Parasitol. 2003;113:189–201
  5. Qablan MA et al (2012) Stray dogs of northern Jordan as reservoirs of ticks and tick-borne hemopathogens. Parasitol Res 111(1):301-307
  6. Adaszek Ł et al (2010) From piroplasmosis to babesiosis--problems with classification of Babesia protozoa isolated from dogs. Wiad Parazytol 56(2):111-115
  7. Kjemtrup AM et al (2006) Babesia conradae sp. Nov., a small canine Babesia identified in California. Vet Parasitol 138:103–111
  8. Criado-Fornelio A et al (2003) Molecular characterization of a Babesia gibsoni isolate from a Spanish dog. Vet Parasitol 117:123–129
  9. Matjila PT et al' (2008) Detection of a Theileria species in dogs in South Africa. Vet Parasitol 157:34–40
  10. Dixit P et al (2010) Evidence of new pathogenic Theileria species in dogs. J Parasit Dis 34(1):29-32