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.