A Q fever outbreak on a dairy goat farm did not result in Coxiella burnetii shedding on neighboring sheep farms – An observational study

Q fever is a zoonotic airborne disease caused by the bacterium Coxiella burnetii. Small ruminants shed tremendous amounts of bacteria during abortion or parturition, resulting in high environmental contamination. From January 2018 to April 2018, a Q fever outbreak occurred on a dairy goat farm with 360 does located on a peninsula in the North Sea. The sheep density on the peninsula was high (108.8 sheep per km2 agricultural land). Therefore, epidemiological investigations were conducted to assess the possible C. burnetii transmission from the positive dairy goat farm to the neighboring sheep flocks. For this purpose, vaginal swabs and serum samples were collected from freshly lambed sheep on twelve sheep farms during the lambing season in 2019. These farms were located within a 10 km radius around the outbreak. Additionally, dust samples from one windowsill of each lambing shed were taken to evaluate the environmental contamination. Sera were examined by ELISA, vaginal swabs and dust samples by qPCR (insertion sequence 1111). Data on wind velocity and direction, precipitation, and humidity from the local weather station were included in the assessment. All vaginal swabs tested negative by qPCR. Only in one dust sample from one farm (8.11 km away) was a low amount of C. burnetii DNA (Cq 38.6) detected. In two flocks, seropositive sheep were present [intra-flock prevalence: 4.5 % (0.94 km away), 7.5 % (3.09 km away)]. The prevailing wind directions came from a westerly direction, with an average wind speed of ≥ 5 m/s. During the Q fever outbreak (January to April 2018), the precipitation was at least equal to the 10-year monthly average, and the humidity was above 80 %. Taken together, the Q fever outbreak on the dairy goat farm did probably not spread to the sheep flocks in the proximity. The precipitation and high humidity during the kidding period possibly prevented C. burnetii from spreading and high wind speeds might have a dilution effect. In the future, the pathogen-animal-environment interface has to be taken into account for future Q fever risk assessments, which is in line with the One Health approach.