Surveys on Coxiella burnetii infections in Swedish cattle, sheep, goats and moose

Abstract

Background: Q fever is a zoonotic disease caused by the bacterium Coxiella burnetii. Prevalence data in ruminant species are important to support risk assessments regarding public and animal health. The aim was to investigate the presence of or exposure to C. burnetii in cattle, sheep, goats and moose, and to compare two enzyme-linked immunosorbent assays (ELISAs). National surveys of antibodies against C. burnetii were performed for dairy cattle (n=1537), dairy goats (n=58) and sheep (n=518). Bovine samples consisted of bulk milk, caprine of pooled milk, and ovine of pooled serum. Antibodies were investigated in moose samples (n=99) from three regions. A one-year regional cattle bulk milk survey was performed on the Isle of Gotland (n=119, four occasions). Cattle, sheep and goat samples were analysed with indirect ELISA and moose samples with complement fixation test. For the sheep, goat, and parts of the cattle survey, samples were run in parallel by ELISAs based on antigens from infected ruminants and ticks. Bulk milk samples from the regional cattle survey and vaginal swabs from a subset of the sheep herds (n=80) were analysed for the agent by polymerase chain reaction. Spatial clustering was investigated in the national cattle survey.

Results: The prevalence of antibodies in dairy herds was 8.2% with large regional differences. High risk clusters were identified in the southern regions. The prevalence among dairy herds on the Isle of Gotland varied from 55.9% to 64.6% and 46.4% to 58.9.0% for antibodies and agent, respectively, overall agreement between agent and antibodies was 85.2%. The prevalence of antibodies in sheep was 0.6%, the agent was not detected the vaginal swabs. Antibodies were not detected in goats or moose, although parts of the moose samples were collected in an area with high prevalence in cattle. The overall agreement between the two ELISAs was 90.4%.

Conclusions: The prevalence of antibodies against C. burnetii in dairy cattle in Sweden shows large regional differences. The results suggest that C. burnetii is a rare pathogen among Swedish moose, dairy goat and sheep. ELISAs based on ruminant and tick antigen performed in a similar manner under Swedish conditions.

Figure 1

Geographical distribution. Dairy herd density on county level and the result of a bulk milk survey used to investigate the prevalence of antibodies against Coxiella burnetii in Swedish dairy cattle (2008/2009), 1411 herds tested negative (blue) and 126 positive (red). The Isle of Öland and the Isle of Gotland are the first and second island, respectively, on the right side of the mainland. The inserted figure is indicating the areas included to investigate the prevalence of antibodies to C. burnetii in moose.

Figure 2

High and low risk clusters. Clusters with more (red lines) or less (blue lines) test positive herds than expected based on analysis of results from a bulk milk survey used to investigate the prevalence of antibodies against Coxiella burnetii in Swedish dairy cattle (2008/2009). Cluster analysis was based on exact coordinates and performed using the spatial scan statistic. The numbers within clusters are the calculated relative risk of each cluster compared to areas outside the cluster. ©Lantmäteriet 2013.

Figure 3

Seasonal variation. Levels of antibodies against Coxiella burnetii measured in bulk milk in 114-119 dairy herds on the Isle of Gotland, Sweden, on four sampling occasions, September 2010 to October 2011.