Theileria orientalis is a tick-borne blood parasite, i.e. it is spread by infected ticks when they feed on an animal's blood.

Theileria orientalis affects both beef and dairy cattle and it can infect cattle of any age. Cows over the calving period and young cattle (two to three months of age) however are most at risk of disease. There are no known human health risks associated with this disease.

Disease incidence on a farm, i.e. the proportion of the herd affected, can be variable. However, most cattle will show no obvious signs of disease but some cattle within a herd will suffer severe disease which, if left untreated, could lead to anaemia and potentially death.

Theileria can enter a property either via infected ticks on animals (including all wildlife) or via Theileria-infected cattle which then infect the local resident tick population.

The disease causes signs associated with anaemia:

  • pale or yellow vulval mucous membranes
  •  whites of eyes are pale to yellow (blood vessels are not clearly visible)
  • cows stay or lag behind the main mob (i.e. they are lethargic)
  • cows do not respond as expected to treatment for conditions such as milk fever
  • cows are off their food and appear hollow-sided in the abdomen
  • there is a decrease in milk production, and a potential for poor reproductive performance
  • there may be poor health and low performance in your young stock
  • there may be deaths especially close to calving or early lactation.

Disease outbreaks can be triggered by stress, particularly around calving time, or even when there is underlying disease and/or certain nutritional deficiencies, e.g. gut parasites, BVD, facial eczema, trace element deficiency.

Treatment of infected cattle with signs of the disease depends on the incidence and severity. Contact your local veterinarian for advice if you suspect animals with the above clinical signs.

Control of ticks is strongly advised particularly if moving cattle from one property to another (especially if there is a known history of ticks) or if there have been signs associated with anaemia in the past. This can be achieved by treating all cattle with flumethrin (e.g. Bayticol® Pour-On) before leaving the property.

Also, check for tick presence on cattle already on the property as treatment with flumethrin may be useful to reduce the tick numbers and severity of disease.

"Haemaphysalis longicornis (cattle tick) before feeding and engorged after feeding"

Lastly, ensure that all underlying causes of stress or concurrent disease are being controlled, e.g. efficient transition and nutritional management, effective parasite control, effective trace element supplementation, monitoring and control of BVD and facial eczema prevention.

Please do not hesitate to contact your local veterinarian for further information and/or advice if you have any concerns.