Since 2006, a deadly cattle disease called theileriosis has swept through Australian herds, spread by bush ticks and causing serious productivity losses for producers.
Here, veterinarian Dr Susan de Burgh of Elanco Australia answers frequently asked questions on bush ticks and theileriosis, and outlines strategies producers can deploy to fight back.
How did this deadly strain of Theileria enter Australia?
Note that the species found in Australia is very different from the Theileria found in Africa and southern Asia. However, the deadly strain of Theileria orientalis (known as ‘Ikeda’) seen in Australia is identical to the species and strain found in Japan. It hasn’t been confirmed how it entered.
It started to cause deaths and disease outbreaks in cattle in about 2006 on the NSW north coast. However, the diagnosis was only confirmed in 2011, by which time the disease had already spread to all parts of the NSW coast and Victoria and caused disease outbreaks on dozens of properties.
It subsequently spread to inland areas of these states and to Queensland, WA and SA as well as New Zealand. So far, it has not been detected in Tasmania or the NT.
Figure 1: Estimated distribution of the bush tick (Haemaphysalis longicornis). Image: Virbac.
How are ticks and Theileria spread?
Even though the bush tick is well-established in a large percentage of cattle grazing areas of Australia, live cattle transport is the main way that both ticks and the Theileria parasites are spread. Because of the tiny size of the tick larvae and nymphs, it’s easy to miss them when bought-in cattle arrive on a property.
Bush ticks will attach to any mammal, so horses, dogs, feral deer and even rabbits could spread the ticks locally.
Theileria parasites require bush ticks to complete their life cycle, but small numbers of parasites can be spread within a herd by sucking lice, or even by mechanical means, like injection needles when vaccinating cattle.
What is the bush tick life cycle?
The life cycle of the bush tick Haemaphysalis longicornis (see Figure 2) is very different from that of cattle ticks (Rhipicephalus australis).
1. The bush tick is known as a ‘three-host’ tick, meaning that it drops off the host every time it moults. It therefore spends a lot of its life on the pasture. To complete its life cycle, it must find and attach to three different hosts.
2. The bush tick population is almost entirely made up of females (estimated ration of females to males is 400 to 1), which are able to reproduce without males (parthenogenesis).
3. Nymph (juvenile) ticks live on pastures over winter, then look for hosts (cattle or other animals) in the spring. Adult ticks are seen on cattle in summer. These lay eggs which hatch and larval ticks can be found on cattle in the autumn.
4. Bush ticks are very small and although their life cycle may take 9–12 months, they may only be visible on cattle for about 14 days of this entire time. This means there could be many bush ticks present in the paddock and even on cattle (as tiny ‘seed’ ticks only about 1mm long) that are invisible to the producer.
Figure 2: Life cycle of the bush tick Haemaphysalis longicornis and transmission of Theileria orientalis infection to cattle in
Identification and treatment
How can you identify disease associated with Theileria?
See your veterinarian for advice on diagnosis and treatment.
Diagnosis of theileriosis is done by matching the clinical signs of anaemia (pale colour, weakness), fever, abortion and loss of appetite with blood tests that can confirm the presence of the disease agent Theileria orientalis and identify the strain.
Can Theileria disease be treated?
There are no specific treatments available to cure infection with Theileria orientalis. Infected cattle and calves may show mild clinical signs, but may also suffer severe illness or death. Treatment is based on intensive care including confinement, intravenous fluids and blood transfusions.
What are the options for stopping ticks and preventing Theileria?
Because Theileria infection is spread by bush ticks, the only preventative available is controlling the ticks.
In places with widespread (endemic) infection, calves pick up the disease soon after birth and have peak disease signs at the age of 8–10 weeks. After this they develop immunity, which only breaks down when they are placed under nutritional or metabolic stress.
Careful handling of calves to prevent situations that exacerbate disease (e.g. mustering over long distances) coupled with extra attention to nutrition and control of other disease conditions helps get them through the critical period.
How to prevent or minimise the impact of Theileria coming onto your property