Theileria in cattle

Theileria species are tick-transmitted protozoa that infect cattle blood cells. Different species and strains vary in severity. In some countries, Theileria orientalis (Ikeda and related genotypes) has caused notable anemia outbreaks after tick expansion or cattle movement.

Also known as: Theileriosis, Oriental theileriosis, Theileria orientalis

• Fever, lethargy, and reduced appetite
• Anemia (pale mucous membranes), weakness, or collapse
• Abortion or stillbirths reported in some outbreaks
• Increased death loss in naïve or heavily challenged herds

Primarily by competent tick vectors. Movement of infected cattle into new tick habitats can establish local risk. Mechanical transmission is generally less central than for anaplasmosis, but veterinary guidance on equipment hygiene still matters.

Cattle in expanding tick ranges, recently introduced stock from endemic areas, and herds under heat, nutritional, or shipping stress. Calves and naïve adults may be heavily affected depending on the strain and exposure.

• Tick surveillance and control consistent with local extension/vet advice
• Quarantine and vet screening when introducing cattle from endemic regions
• Reduce concurrent stressors (heat, poor nutrition, rough handling)
• Pasture and facility plans that limit peak tick exposure where feasible
• Coordinate with your veterinarian on herd monitoring if theileriosis is diagnosed nearby

• Merck Veterinary Manual — Theileriosis
• USDA APHIS — Livestock disease information

• Heat stress (THI)
• Cold stress
• Location / climate snapshot