Coxiella burnetii: Decline of antibody response in pluriparous dairy cows during dry period and maternal antibody levels in dairy calves in an endemically infected herd

Coxiella burnetii (C. burnetii), an intracellular zoonotic bacterium causing Q fever, is widely distributed in cattle herds. In this study, we investigated changes in antibody response during dry period in dairy cows and the course of maternal antibody levels in dairy calves by using a commercial ELISA. In a total of 35 pluriparous cows, the proportion of seropositive animals (65.7% vs. 42.9%) (p = 0.039) and the mean antibody score levels (2.8 ± 2.4 vs. 1.0 ± 1.4) (p < 0.001) declined significantly from dry cow therapy to calving. During this period, 2/12 (16.7%) formerly seronegative cows seroconverted, whereas in 10/23 (43.5%) of the seropositive animals a seronegativization occurred. C. burnetii DNA was detected by PCR in 15/35 (42.8%) of the vaginal swabs obtained immediately after calving. All twelve calves enclosed in this study were born seronegative and precolostral whole blood samples of the calves were tested negative by PCR for C. burnetii DNA. After colostrum intake, 7/12 (58.3%) of these calves seroconverted and stayed seropositive until day 33. Afterwards, the proportion of seropositive calves and the antibody scores decreased gradually. From day 103 after birth on, all calves remained seronegative. In conclusion, we recommend the exclusion of cows for the period of colostrogenesis and calves after colostrum intake from seroepidemiological investigations to avoid bias.