Is there a connection between the vaccination against Q fever (COXEVAC®) and the consumption of antibiotics in dairy farms?

Background. Q-fever is caused by the zoonotic pathogen Coxiella burnetii and can lead to abortions, miscarriages and weak calves in dairy cows. Since 2010, it is possible to vaccinate cows against Q-fever with the vaccine COXEVAC^® (Ceva Santé Animale). It was the aim of this study to examine whether the usage of the vaccine could reduce the consumption of antibiotics in dairy farms.

Methods. In this case-control study, 49 dairy farms from Northern Germany (Lower Saxony) participated (36 farms with vaccination (V) and 13 farms without vaccination (C)). In all herds, Coxiella burnetii had been directly (antigen detected with PCR (polymerase chain reaction) in fetus, placenta, cervix swabs or milk) or indirectly (antibodies detected in serum or milk) diagnosed. The study period lasted three years. For V, timepoint 0 (t0) was the day when farms finished the basic immunization with COXEVAC^®. For C t0 was four weeks after a positive diagnosis of Coxiella burnetii. Period 1 (P1) was the year before t0. Period two (P2) and three (P3) spanned the first and second year after t0. The consumption of antibiotics for each farm was collected my means of the veterinary documents about the application and delivery of antibiotics. The therapy frequency (TF) of the cows (lactation number ≥ 1) was calculated (TF: sum of single doses per cow and period divided through the mean number of cows in that period). The mean therapy frequency of the study groups was compaired between the vaccinated and the control group. Additionally, the used amounts of 12 antibiotic classes (sum of gram per cow and period divided through the mean number of cows in that period) were recorded.

Results. In P1, the mean TF did not differ significantly between the study groups (V: 5.42, C: 5.82; p=0.217). In C, the mean TF increased over time (P2: 6.42, P3: 7.28) whereas in V, the mean TF slightly decreased (P2: 5.30, P3: 5.11). In P3, the difference between V and C was significant (p=0.024). Considering the amounts of antibiotic drugs used for each cow, only two drug classes exhibited a significant difference between V and C in P3. Those were the class of tetracyclines (V: 2.24 g, C: 4.51 g, p=0.019) and the class of β-lactamase inhibitors (V: 0.036 g, C: 0.085 g, p=0.049).

Conclusions. The present results might suggest that there is an association between the vaccination against Q-fever and a reduced consumption of antibiotics. Further studies are necessary to elucidate the cause-effect relationship between vaccination and the consumption of antibiotics on dairy farms. The major challenge will be to include the multiple factors influencing the consumption of antibiotics on commercial dairy farms.