Prevalence of Coxiella burnetii in German sheep flocks and evaluation of a novel approach to detect an infection via preputial swabs at herd-level

Abstract

A prevalence study was conducted on German sheep flocks including goats if they cohabitated with sheep. In addition, a novel approach was applied to identify an infection at herd-level before lambing season with preputial swabs, suspecting (C.) burnetii. Blood samples and genital swabs were collected from breeding males and females after the mating season and were analyzed by ELISA and qPCR respectively. In total, 3367 animals were sampled across 71 flocks. The true herd-level prevalence adjusted for misclassification probabilities of the applied diagnostic tests using the Rogan-Gladen estimator for the prevalence estimate and a formula by Lang and Reiczigel (2014) for the confidence limits, ranged between 31.3-33% (95% confidence interval [95% CI] 17.3-45.5) detected by ELISA and/or qPCR. Overall 26-36.6% (95% CI 13-56.8) were detected by ELISA, 13.9% (95% CI 4.5-23.2) by qPCR and 7.9-11.2% (95% CI 0.1-22.3) by both tests simultaneously. The range of results is due to data obtained from literature with different specifications for test quality for ELISA. Among eight farms with females shedding C. burnetii, three farms (37.5%) could also be identified by preputial swabs from breeding sires. This indicates less reliability of preputial swabs if used as a single diagnostic tool to detect C. burnetii infection at herd-level.