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 the herd-level before lambing season with preputial swabs, suspecting venereal transmission and ensuing colonisation of preputial mucosa with Coxiella (C.) burnetii. Blood samples and genital swabs were collected from breeding males and females after the mating season and were analysed by enzyme-linked immunosorbent assay (ELISA) and quantitative polymerase chain reaction (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% and 33% (95% confidence interval [95% CI] 17.3–45.5) detected by the 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 the qPCR and 7.9–11.2% (95% CI 0.08–22.3) 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 the herd-level.

Risk factors for an infection with Coxiella burnetii in German sheep flocks

“…Some of the variables obtained from the questionnaire and the sample list were identified as being associated with an increased C. burnetii infection hazard. However, the data gathered from the questionnaire were included in the study for prevalence estimation in 71 German sheep flocks [10] and no sample calculations were undertaken for subsequent risk factor analysis. The lack of significant impact of some risk factors could be due to the limited numbers of farms and the huge variability in farm management and husbandry.…”

“…The current risk factor analysis of a C. burnetii infection is based on data taken from a recently published prevalence study. Details of farm and animal selection, sampling procedure and laboratory tests are published elsewhere [10].…”

“…Moreover, the geographical location was dichotomised (North = SH, LS, NRW; South = BAV, BW) to reduce results' distortion. Due to the deviating infection rates and the different farm management systems in these two regions [10], the geographical location of the examined farms was considered as a confounder and therefore the model was stratified for the two regions.…”

“…In contrast, lambing sheep were identified as a primary source of human C. burnetii epidemics in Germany, where a number of small-scale outbreaks occurred within the last two decades with a maximum of 331 infected individuals in one of the outbreaks [9]. A recently conducted study revealed a herd prevalence of 26–36.6%; 13.9% of C. burnetii -positive sheep flocks in Germany detected using ELISA and qPCR, respectively [10].…”

Comparison of Coxiella burnetii Excretion between Sheep and Goats Naturally Infected with One Cattle-Associated Genotype

“…The highly contagious pathogen infects animals and humans particularly through the inhalation of contaminated aerosols or dust and no direct contact to shedders is necessary. Sheep and goats are the main reservoirs for the pathogen and the herd prevalence is over 30% in several countries [5][6][7]. Consequently, small ruminants are the major source for many human Q fever epidemics in Europe [8].…”