Theileriosis

• Cause:
  • Theileriae are obligate intracellular protozoan parasites that infect both wild and domestic bovidae throughout much of the world.
  • Theileria parva is responsible for East Coast Fever in Eastern and Central Africa.
    • Buffalo-derived Theileria parva is responsible for a related condition known as "Corridor disease", a fatal condition of cattle. It was previously believed that the two diseases were caused by two separate Theileria parasites, T. parva parva and T. parva lawrencei.  However, genetic analysis has concluded that these two diseases are caused by the same parasite, T. parva, with differences in pathogenicity and virulence. 
  • Theileria annulata is responsible for tropical theilerioses in Mediterranean countries.
  • Theileria orientalis is found worldwide, but countries affected by clinical oriental theileriosis include Australia, New Zealand, Japan, Korea, China, Vietnam and the United States of America. The Asian Long-horned tick is the vector for T orientalis Haemophysalis longicornis . 11 genotypes of T orientalis have been identified:
    • Theileria orientalis chitose (type 1) – associated with severe disease.
    • Theileria orientalis ikeda (type 2) – associated with severe disease outbreaks in Asia, Australia, New Zealand and the US.
    • Theileria orientalis buffel (type 3) has been reported in the UK but is considered non-pathogenic.
    • Types 4 to 8 and N1 to N3 have also been identified.
• Signs: see below.
• Diagnosis: indirect fluorescent antibody test; Giemsa stained impression smears form the blood or lymph nodes in live animals, or from most internal organs in necropsies; PCR.
• Treatment: anti-protozoal drugs, such as buparvaquone, parvaquone, and halofuginone and the antimicrobial oxytetracyline have been advocated.
• Prognosis: guarded.

Geographic incidence

• Worldwide.

Age predisposition

• All age groups may be affected.

Breed/Species predisposition

• European Bos taurus types are more susceptible than indigenous Bos indicus based breeds of cattle.

Public health considerations

• None.

Cost considerations

• Depressed milk production, abortions, still births and mortality.

Special risks

• Anesthesia in hypovolemic animals Anesthetizing cattle.