Infection rates and outbreaks of disease due to Babesia argentina in unvaccinated cattle on 5 beef properties in south-eastern Queensland.

Serums from unvaccinated groups in 5 herds of beef-cattle in South-East Queensland were tested for antibodies to Babesia argentina at intervals while the cattle were increasing in age from about 6 months. An indirect fluorescent antibody test was used. Infection rates, indicating the proportions of the groups that had been exposed to tick-transmitted infection were 49.2, 56.9 and 69.1% for cattle aged approximately 6, 12 and 18 months, respectively. The degree to which cattle were infested with the vector, Boophilus microplus, was estimated. There appeared to be a strong correlation between infection rate and tick incidence. Four serologically negative animals died of either confirmed or suspected babesiosis during the sampling period. Sickness was observed in 5 others. The serological status of 57 changes from negative to positive without symptoms being observed, indicating relatively low mortality and morbidity rates in the enzootic situation studied.