Theileria orientalis is the blood parasite that causes ‘benign theileriosis’ and has been present in Australia for more than 100 years. Historically, it has rarely caused disease. Since late 2005 there has been an increase in the number, severity and distribution of cases due to Theileria orientalis infection in cattle in eastern Australia.
DNA testing of Theileria orientalis revealed new strains of the parasite that had been previously undetected in Australia. It is now believed that the change in disease dynamics is due to the presence of the ‘Theileria orientalis Ikeda’ strain. The disease syndrome is called bovine anaemia due to Theileria orientalis group (BATOG) or ‘oriental theileriosis’.
BATOG is not caused by the exotic parasites Theileria parva and Theileria annulata. These parasites cause the exotic diseases East Coast fever and tropical theileriosis.
BATOG does not have any market access or human health implications.
BATOG was first detected in WA’s Lower Great Southern region during May 2013 and has also been found in South-West WA. Testing has shown the ‘Ikeda’ strain of the organism is responsible for the cases of BATOG in WA. A survey over the summer of 2014-15 revealed that approximately 50% of the sampled cattle farms in one area were infected with the ‘Ikeda’ organism. Some farms reported considerable cow losses and abortions when the disease was first detected, while on other infected farms no disease was noted. It is thought that the more severe effects on some farms were due to animals being first exposed to BATOG during the calving period.
How is BATOG spread?
The Theileria orientalis parasite is spread predominately by the bush tick. The bush tick is found on cattle, but also readily infests many other warm-blooded animals including other livestock, wildlife, birds, dogs and cats. The bush tick has been found in the Lower Great Southern and South-West, however the complete range of its distribution in WA is currently unknown.
Bush ticks survive in cool, moist environments where there is shade and protection provided by plant foliage. The bush tick typically prefers areas with year-round rainfall and temperate summers, such as coastal areas of the Lower Great Southern. Even in favourable environments, the ticks require a moist, sheltered ground environment. Short, open pastures away from the coast are usually too dry over summer to permit survival of the free-living stages.
The bush tick requires three different hosts to develop. Each developmental stage spends only up to 10 days on the host. Nymphal stages and unfed adults are small and often difficult to see on cattle. Adult ticks are seen mainly during early summer, while larvae are seen in late summer to early winter and nymphs in spring.
The most common sites of attachment on cattle are around and beneath the tail head, between the hind legs and udder skin folds, underneath to the elbows and escutcheon. In heavy infestations they are also found on or in the ears.
The presence of bush ticks on cattle does not mean that the herd has BATOG, only that the carrier is present. The infective parasite Theileria orientalis is also required for herds to develop BATOG.
Cases of BATOG have also occurred where no obvious evidence of bush ticks on cattle was seen, however it is difficult to confirm the presence of a low number of ticks and the ticks may be gone by the time clinical signs of BATOG occur.
Which stock are most affected by BATOG?
Cattle under stress are most affected by BATOG. This includes late pregnant and recently calved cows, aged cows and young calves (2-3 months old).
Often only a small proportion of animals in BATOG herds will show obvious signs of disease. However, it is likely that the majority of the herd is infected and the other animals have developed immunity without showing signs of illness.
Cattle in areas where BATOG is established will develop immunity with the severity of disease decreasing in following years. In affected areas of eastern Australia, disease in cows is now rare but young calves and newly introduced cows can still be affected. Once infected, animals remain infected for life and the disease may re-emerge during periods of stress, particularly around late pregnancy or calving.
Signs of BATOG
The signs associated with BATOG are due to the destruction of red blood cells. Common signs, particularly in late pregnant or recently calved animals, include:
- anaemia and pallor
- red urine
- jaundice (yellowing of mucous membranes)
- late stage abortions and premature births
- sudden death.
Other signs include:
- listlessness or depression
- lack of appetite or weight loss
- wobbly gait
- laboured breathing.
Note that the signs of other diseases can be similar to BATOG, so it is important to confirm the diagnosis with laboratory testing. Diseases that can look similar to BATOG include trace element imbalances, milk fever and leptospirosis.
There are no drugs registered for the treatment of BATOG in Australia.
Providing low stress nursing care is critical for affected animals. Do not move affected animals long distances. They should be provided with good feed, fresh water and shade. Multivitamins may be beneficial and blood transfusions can be considered in valuable animals. Tick treatments may be indicated when individual animals are suffering from blood loss due to the number of ticks.
In general, antibiotics and Imidocarb as treatment for acute cases have not been found to be effective by Australian or New Zealand veterinarians. Buparvaquone is not registered in Australia due to the persistence of chemical residues that would impact our export markets.
Note: Off-label use of veterinary chemicals is permitted in individual cattle, but the veterinarian must provide to the owner of the animal an off-label written statement, which includes an appropriate meat and/or milk withholding period, which ensures treated animals are free of chemical residues at slaughter. For information on the supply of off-label veterinary chemicals, see the webpage Veterinary chemical users.
Managing cattle in BATOG areas
Maintaining a healthy herd by implementing good management practices is essential to minimise the effect BATOG has on your herd.
Management plans should be made in consultation with your private veterinarian.
These plans should focus on:
- maintaining good nutrition
- providing appropriate mineral supplementation (e.g. copper, cobalt and selenium)
- an up-to-date vaccination program (e.g. vibrio, leptospirosis, bovine viral diarrhoea virus)
- strategic drenching and parasite control
- close monitoring of cattle (particularly before and during calving)
- treatment and management of clinically unwell cattle.
Attempts to control ticks on cattle are not expected to be effective in preventing BATOG. The bush tick only spends a small amount of time on animals and most of their life on pasture. They are also hard to detect in their immature stages.
Cattle movement and BATOG
BATOG is likely to only be seen where the bush tick is present. Movement of infected cattle may hasten the movement of BATOG to new areas where the tick occurs.
When buying new cattle, it is important to assess the risk of them contracting or carrying BATOG when they arrive on your property.
Naïve cattle (i.e. cattle that have not been exposed to BATOG) are the most likely to be severely affected if they contract BATOG during pregnancy or calving. Ensuring cattle are purchased as healthy replacement heifers with time to be exposed and develop immunity to BATOG before becoming pregnant may decrease the risk of BATOG-associated losses.
When selling or moving cattle from known BATOG areas to properties outside BATOG areas, treat animals before movement with a minimum of a macrocyclic lactone (ML) or combination drench and an insect growth regulator (IGR) to reduce the movement of ticks with the cattle. The establishment of the bush tick on new properties will depend on the local environment.
If cattle destined for abattoirs or saleyards are treated, ensure you observe the withholding period (WHP) of any products used.
What do I do if I suspect BATOG in my cattle?
There are subsidies available for testing of cattle showing signs of BATOG.
If you suspect your cattle may have BATOG or another disease, call your private veterinarian or local DPIRD Field Veterinary Officer.
Producers play a vital role in Western Australia’s animal health surveillance system, which helps protect our $2 billion annual export market.
You can find your nearest DPIRD Field Veterinary Officer contact on the Livestock Biosecurity contacts page.