Diagnostic methods used to monitor an outbreak of babesiosis (Babesia bovis) in a herd of feral cattle in New Caledonia.

Abstract

BACKGROUND: In December 2007, Babesia bovis was introduced to New Caledonia through the importation of cattle vaccinated with a live tick fever (babesiosis and anaplasmosis) vaccine. Medical measures, acaricide and antiprotozoal treatments, and quarantine restrictions were implemented with success on all the farms involved, but the disease spread to one of the neighbouring properties where feral cattle were present. To circumscribe and eliminate this outbreak, the authorities decided to slaughter all animals on the neighbouring property. OBJECTIVES: To monitor the spread of babesiosis in naïve cattle and to compare the usefulness of PCR, ELISA and brain smear for disease detection in monitoring this outbreak. METHODS: Blood and brain samples of slaughtered animals were analysed over time throughout the eradication campaign using serology, PCR and brain smears. In addition, field numbers of Rhipicephalus microplus tick larvae were assessed and Babesia infection of the larvae analysed using PCR. RESULTS: This study showed the natural spread of babesiosis in a naïve herd without pharmacological control measures. Prevalence reached 80% within a year of introduction. ELISA and PCR tests performed similarly in detecting disease in cattle and both were superior to brain smears. Nevertheless, specific tests or combinations of tests may be preferable, depending on the specific requirements of any future disease situation. CONCLUSIONS: In cattle, ELISA and PCR appear to be suitable tools for monitoring the evolution of a babesiosis outbreak, with brain smears as a useful adjunct. PCR was not suitable for detecting infection in tick larvae.