Tick Fever in Cattle

(Babesia and Anaplasmosis)

Tick fever is caused by infection with Babesia and Anaplasma organisms transmitted by the cattle tick Rhipicephalus australis (formerly known as Boophilus microplus). All cattle in tick infested areas are at risk of developing tick fever. Breed and age are key risk factors.

British, European and other Bos taurus breeds are more susceptible to tick fever caused by Babesia than Brahman/Bos indicus breeds. All breeds, including Bos indicus breeds, are highly susceptible to disease caused by Anaplasma marginale.

There is a strong link between age and resistance. Calves exposed to tick fever organisms between 3–9 months of age rarely show clinical symptoms and develop a solid, long-lasting immunity. Once infected with Babesia or Anaplasma organisms, the animals become carriers and the infection and immunity is likely to persist for many years. A tick fever vaccine is available in Australia.

The single biggest risk for disease caused by infection with tick fever is in cattle that are introduced from outside the cattle tick areas. However, even cattle born and raised within the tick area are not guaranteed to have developed immunity by the time age-related resistance wanes at 9–10 months of age.

Babesiosis

Babesiosis (also known as red water) is caused by either of the organisms Babesia bovis or Babesia bigemina, both of which are transmitted by the cattle tick. Babesia bovis is only transmitted by cattle tick larvae on pasture; Babesia bigemina is transmitted by the nymph or adult stages of cattle tick.

Babesia bovis (Figure 1) is the most important cause of tick fever disease in Australia; it is responsible for more than 80% of tick fever outbreaks. The course of the disease is quite rapid, and death can occur within a day or two of first observing clinical signs.

Signs

• Fever, lethargy, depression and weakness.
• Pale and/or yellow mucous membranes (anaemia and/or jaundice).
• Loss of appetite.
• Staggered gait.
• Muscle tremors.
• Red urine (especially with B. bigemina; in latter stages with B. bovis).
• Nervous signs such as charging or head pressing may be a feature of the later stages of Babesia bovis infection.
• Abortion may occur in cows.
• Temporary infertility in bulls.

Diagnosis

Many of these clinical signs are non-specific and can be associated with other conditions, so it is important to confirm the diagnosis by examination of blood smears under a microscope.

Treatment and control

See these pages for the treatment and control of tick fever.

Anaplasmosis

Anaplasmosis is caused by the organism Anaplasma marginale (Figure 1). It is transmitted by the cattle tick and is thought to be transferred mainly by direct movement of male ticks from carrier animals to other animals when they are in close contact. The course of the disease is more gradual than that associated with babesiosis, and the animals may be quite anaemic and jaundiced by the time clinical illness is noted.

Signs

The main clinical signs are pale and/or yellow mucous membranes (anaemia and/or jaundice); note that the urine does not turn red with anaplasmosis but may appear as a dark brown colour. Other clinical signs of anaplasmosis may include fever, loss of appetite, lethargy and depression, weakness and loss of condition.

Diagnosis

As with babesiosis, many of these clinical signs are non-specific and can be associated with other conditions, so it is important to confirm the diagnosis by examination of blood smears under a microscope.

Treatment and control

See these pages for the treatment and control of tick fever.