MONITORING BABESIA-BOVIS INFECTIONS IN CATTLE BY USING PCR-BASED TESTS

The sensitivity and specificity of PCR tests based on the small-subuni t rRNA gene sequence of Babesia bovis were compared in a blind study o f experimentally infected cattle with the corresponding parameters of the complement fixation (CF) test currently used in the United States to screen for bovine babesiosis. Cattle were experimentally infected w ith a single inoculum of a cloned laboratory strain of B. bovis. Blood samples were collected and tested over a period covering from the day of infection to 10 months postinfection, The level of parasitemia (pe rcent infected erythrocytes) present in each sample was estimated from test results and was plotted as a function of time postinfection. The se data are the first describing the course of infection by methods ca pable of detecting parasitemias in the range of 10(-7)%, which frequen tly occur in the carrier state, Parasitemias in the samples tested str ongly influenced the sensitivity and negative predictive value of the PCR-based tests which varied with time postinfection, The average sens itivities of the three PCR-based tests for B. bovis ranged from 58 to 70% for a single determination, while the sensitivity of the CF test w as only 6%. Both PCR-based and CF tests for B. bovis had high specific ity values ranging from 96 to 100%.