Theileria

Theileriosis is a tick borne disease that infects both red and white blood cells of cattle, caused by organisms of the Theileria group. Theileria has no human health implications.

It reduces oxygen supply in sick cows, causing anaemia and weakness, and may lead to the collapse of the animal. While in most cases cattle are known to fully recover from the disease, in some instances it can result in death, particularly among animals under stress.

There is currently no vaccine available and no registered treatment for theileriosis in Australia.

Producers who see cattle showing unusual signs of weakness along with a lack of appetite should contact their veterinarian for assistance.

Where the disease is found

Found primarily in high rainfall areas of the state, the disease was first confirmed in South Australia in healthy animals in 2012, with subsequent small clinical outbreaks occurring in 2014, 2016 and 2017.

The strain of Theileria seen in Australia is usually mild or 'benign' and is endemic in the high rainfall areas of New South Wales and Victoria. The greatest areas of risk in South Australia are:

• the lower South East
• Kangaroo Island
• Yorke and Eyre Peninsulas.

The disease can be more severe when it moves into new areas, where animals not previously exposed can be affected.

Symptoms and diagnosis

Theileria is an organism that is able to lie dormant for a long period. It usually emerges after a period of good rain when tick numbers increase and facilitate the spread of the disease.

Clinical signs for theileriosis include:

• anaemia
• lethargy (lack of willingness to walk)
• weakness
• fever
• jaundice (yellowing/pale gums)
• increased heart rate
• difficulty breathing (gasping if forced to run)
• reduced milk production
• abortions
• still birth
• dystocia
• death.

As these symptoms can also be linked to other conditions, it is important to confirm diagnosis with your veterinarian. Diagnostic tests include microscopic examination of the blood, antibody tests and PCR (polymerase chain reaction, which detects the DNA of the organism).

Care for affected animals

While most cattle infected usually don’t become sick, those under stress may show signs of illness, such as:

• dairy cattle in peak lactation
• cows to calve, or have recently calved.

Individually nursing affected stock is recommended, along with minimising stress and movement.

Avoid handling affected cattle where possible and if movement or yarding is necessary, transfer animals slowly.

Providing high quality feed is also recommended.

Spread between animals

In addition to the direct contact by ticks, the disease can spread by multiple use of vaccination guns, ear taggers or other animal husbandry devices that have been in contact with blood.

Given the way disease can be spread, quarantining affected stock on the property is not an effective mitigation tool.