Assessment of an indirect fluorescent antibody test for the detection of antibodies specific for Pajaroellobacter abortibovis in adult cattle

A highly specific, sensitive, and reproducible indirect immunofluorescent antibody test (IFAT) capable of detecting antibodies bound to Pajaroellobacter abortibovis was previously described and validated for use with bovine fetal fluid. Similar validation has not been demonstrated with cow sera. Adult cattle show no sign of infection with P. abortibovis prior to abortion and therefore it is difficult to identify exposed animals. To address this problem, paired sera from 107 dams, that had lost calves due to EBA, were tested by the P. abortibovis-specific IFAT. Specificity and sensitivity were determined by comparing IFAT antibody titers before P. abortibovis exposure to those at or near the time of EBA abortion. Fifty-six samples from a combination of experimental negative controls and animals originating from non-endemic areas were added to increase the sample size when calculating specificity. None of the 107 sera collected from cows prior to Pajaroellobacter abortibovis exposure had detectable IFAT titers (i.e. <200), nor did sera from non-endemic (n = 46) and negative control cows (n = 10). In contrast, P. abortibovis-specific antibodies titers of ≥ 200 were detected in all 107 serum samples collected at or near the time of an EBA abortion. Specificity and sensitivity for dam sera were both established at 100 % when cutoff criteria for positive tests were assigned a titer of ≥ 200. This P. abortibovis-specific IFAT is a powerful tool for identifying exposure to the etiologic agent of epizootic bovine abortion in adult cattle and will facilitate future studies to better define the geographic distribution of the disease.