Vet's vision with Phil Rennie Tauranga Vets

 Theileriosis continues to be a significant issue on farms heading into another blood-sucking summer in the upper North Island.

The disease is caused by the parasite Theileria orientalis and is spread by infected cattle ticks when they feed on the animals’ blood. See the typical annual life cycle of a tick below for seasonal pattern of infestation.

The disease affects both beef and dairy cattle and it can infect cattle of any age. Cows over the calving period and potentially young cattle (two to three months of age) are most at risk of disease. Fortunately, there are no human health risks associated with this disease.

Specifically targeted are young calves or previously unaffected adult cows with a history of grazing off-farm where infected tick populations are high. The disease typically manifests itself at times of high stress, such as early lactation for milking cows that are transitioning into peak milk production. In the case of calves demands of rapid growth/ dietary transition is typical, especially when environmental and other disease challenges are present.

Most cattle will show no obvious signs of disease but some cattle within the herd with Theileria can progress to severe anaemia and potentially death if left untreated.

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.

Signs of disease associated with anaemia include the following:

• Cows are lethargic and lag behind the main mob.
• 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.
• Pale or yellow vulval mucous membranes and/or whites of eyes.
• 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. Gastrointestinal parasites, BVD virus, facial eczema challenge, trace element deficiencies.

Control of ticks is strongly advised particularly if moving cattle from one property to another. This applies especially if moving from a more Northern property or there is a known history of ticks with signs associated with anaemia in the past. This can be achieved by treating all cattle with products containing the active ingredient flumethrin before leaving the property or on arrival before mixing with other cattle.

If cows or heifers are being grazed off-farm onto a property with a history of Theileria and/or a high tick population, treatment is ideally applied five days before the cattle are moved and repeated as often as every three-six weeks (typically monthly) while away grazing to reduce the risk of infection of bringing the disease back to the home property.

Where possible ensure 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.

Successful treatment of cattle infected with Theileria depends on the incidence and severity.

Feel free to contact your local vet clinic for further information and/or advice if you have any concerns about your cattle.