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Theileriosis

Theileria orientalis is transmitted by ticks of the genus Haemaphysalis (Bush tick – H longicornis, and Wallaby tick – H bancrofti), but can also be transmitted on injection needles, and possibly by biting insects.

Theileriosis in Australia is caused by the blood parasite Theileria orientalis. The T. orientalis buffeli variant has been present for more than 100 years but has historically been benign, causing only mild anaemia in cattle. Infections have only rarely been severe enough to cause significant morbidity or mortality. Cattle clinically sick with theileriosis are typically infected with T orientalis ikeda, with or without T orientalis chitose.

Conditions where theileriosis is likely to occur

The parasite is now endemic in many coastal regions of New South Wales, Victoria and Queensland and has been detected in all states and territories except Tasmania. Until recently, only two sub-clinical cases had been recorded in Western Australia and the first outbreak in South Australia was recorded in October 2014.

Identification and diagnosis

Young cattle (2-3 months old), cows in late-pregnancy and recently calved cows are most likely to be affected.

More common signs, particularly in late pregnancy or early lactation, include:

  • pale gums and membranes around the eyes due to anaemia
  • fever
  • lethargy and weakness
  • red urine
  • jaundice
  • death
  • late-stage abortions
  • premature births.

Other signs include:

  • listlessness
  • lack of appetite, weight loss
  • wobbly gait
  • laboured breathing.

A diagnosis of theileriosis can be confirmed by examination of a stained thin blood film under a microscope, but distinction between buffeli / ikeda / chitose can only done by molecular identification in a suitably equipped laboratory.

Prevention

There is currently no vaccine available for theileriosis. There are, however, other tools that can be employed to prevent an incursion in their herd. These are:

  • General biosecurity principles such as avoiding importing animals into your herd from known infected properties.
  • Consider using acaricides to minimise tick burden in your herd, and also grazing susceptible paddocks with other species.

Avoid stressing animals that you suspect of being infected with theileriosis to prevent compromising the movement of oxygen in their body any further. This includes avoiding too much movement and ensuring they have adequate water and good feed available to them.