Theileria

Theileriosis is a disease caused by a species of Theileria – a blood-borne parasite. It only affects cattle and is primarily transmitted by ticks. Theileria is a widespread disease with an increasing number of cases in the northern parts of the North Island. We have witnessed news cases appearing in the geographical area covered by Franklin Vets.

To become infected by Theileria, a cow must be bitten by a tick carrying the disease. It is not spread by direct animal to animal contact. Cattle can be infected with the Theileria parasite without necessarily showing any signs of clinical disease.

Theileriosis only affects cattle and is transmitted by cattle ticks
Theileriosis causes anaemia in cattle and can sometimes be fatal
Cows during calving and young calves (2-3 months) are at most risk from infection.

Once the animal is bitten, it takes about 6-8 weeks for the parasite to build up significant levels in the blood. At this stage, the body reacts by trying to destroy the parasite. Because the parasite is living inside the red blood cells, the body attacks its own infected red blood cells (haemolysis) to destroy the parasite. Unfortunately, this can lead to a huge loss in red blood cells which are responsible for carrying the oxygen around the body; this is known as anaemia and results in the following signs in affected animals:

Pale or yellow, rather than healthy pink, vulva (open up the vulva and look at the colouring inside)
Pale or yellow whites of eyes (a sign of jaundice)
Lethargy – exercise intolerance, cows lagging on the walk to the shed
Sick cows not responding as expected to treatment for conditions such as milk fever
Cows are off their food and appear hollow sided
A decrease in milk production
Sudden death especially in late pregnancy or early lactation.

The signs of anaemia associated with Theileriosis are more likely to be seen around calving time, in calves (2-3 months), and if cows are coping with other health challenges, or potentially at mating time.

If you notice any of the above signs or would like more information about Theileria, please contact us.

Assessment can be determined by:

Assessment of the herd - Use the vulva colour guide to screen the herd and see how many animals might be affected
Red Blood Cell Count (PCV) - Blood sample suspected animals. A low PCV is an indication of severe blood loss.

Control & Prevention of Theileria

Cattle are at risk of infection when moved to areas where infected ticks are present. Infected animals can also spread the infection to ticks when transported to new areas. In turn, this can spread the disease to uninfected animals.
Tick control is important during the risk period. This is commonly mid-August to mid-March, but as long as the mean air temperature is above 7˚C ticks will be active to some degree. Tick control is also important during periods of stress, for example, calving and peak milk production.
New arrivals and returning stock should ideally be quarantined for at least 7 days to check and treat ticks.
Ensure all stock being transported to new areas are healthy and free from ticks.
Observe cattle regularly during the risk period.
Apply tick control products during the risk period. Franklin Vets recommend Flumethrin and Python for cows.
Treat other animals (hosts) on the farm for ticks.

Prevention is not possible in areas where ticks are present. For people moving stock into areas with ticks, we would strongly advise that you carry out blood tests to determine if the animals being moved have been exposed to the parasite. If they have been exposed then there should be relatively little risk of them developing clinical disease, however, if they haven’t come across the parasite before then they will be at a high risk of breaking down with clinical Theileriosis.

Avoid exposing naïve animals to infected ticks 6-8 weeks prior to calving /peak milk production.

Consult a Franklin Vets veterinarian for advice on tick control and Theileria on your farm.

Treatment

Once the diagnosis of theileriosis is made, the most appropriate treatment depends on a variety of aspects including the clinical signs, the number of affected animals and feed availability.