Ruminants are recognized as the main reservoirs of Coxiella burnetii. EFSA highlighted the lack of knowledge about Q fever prevalence in many European countries. A cross-sectional study was carried out in randomly selected dairy herds (n = 109) from central Portugal to screen for C. burnetii infection and to correlate it with herd factors. Bulk tank milk (BTM) samples from cattle (n = 45) and small ruminant (n = 64) herds were tested by ELISA and PCR. The apparent seroprevalence of Q fever was estimated in 45.9% (95% CI: 36.3-55.7) being higher in small ruminants (51.6; 95% CI: 39.6-63.4) than in cattle (37.8; 95% CI: 25.1-52.4). The shedding of C. burnetii in BTM was detected in 11.9% (95% CI: 7.1-19.4) of BTM, and it was higher in cattle (20%; 95% CI: 10.9-33.8) than in sheep and mixed herds (6.3%; 95% CI: 2.5-15). A high bacterial load (≥ 3 × 10(3) bacteria/ml) was observed in 85% of PCR-positive BTM. A significant correlation was found between the bacterial load and positive samples on ELISA (P < 0.001). Antibody positivity was significantly associated with the increased herd size (P < 0.01) and the occurrence of abortion (P < 0.05), whereas the shedding of C. burnetii was significantly associated with the report of infertility (P < 0.05). The results highlight that serological and molecular methods in combination are a useful tool to screen for Q fever and to clarify the herd infection status. The shedding of C. burnetii through milk is important, especially in dairy cattle, and thus, the role of milk as a potential source of infection among dairy workers should not be neglected. To our knowledge, this is the first study reporting C. burnetii infection in dairy livestock in Portugal showing that Q fever is significant in dairy herds, leading to economic losses and being a risk for public health, which highlights the need of implementation of control measures.
Keywords: Coxiella burnetii; ELISA; Epidemiology; dairy ruminants; qPCR.
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