Abstract :

The aim of the PhD thesis was to assess the effectiveness of different medical measures to control Coxiella burnetii (Cb) infection in clinically affected dairy herds. To reach that goal, a multicentric trial was conducted in 120 commercial affected dairy herds. At inclusion time, one strategy among four was randomly assigned to each herd corresponding to (in addition to the systematic vaccination of heifers): (i) vaccination of dairy cows, (ii) use of antibiotics at drying off, (iii) the combination of vaccination and antibiotics and (iv) no action on dairy cows. After having evidenced very wide levels of seroprevalence in dairy cows, contrary to heifers which were quite systematically seronegative and having confirmed the informative value of an ELISA applied on bulk tank milk to assess the seroprevalence of Q fever in dairy cows, the effectiveness of the 4 medical strategies was assessed through a 13 months follow-up of Coxiella burnetii shedding at both individual and herd levels. Vaccination of dairy cows, in addition to that of heifers, was associated with a reduction of Cb bacterial load measured at individual level (in vaginal mucus at calving time) and at herd level (in bulk milk and environmental samples). Tetracycline injection once at drying off was associated with a lower risk of Cb shedding in vaginal mucus at calving time. The present results provide useful knowledge to elaborate evidence based control scheme towards Q fever control in dairy cattle.

Key words :

Cattle, Q fever, Coxiella burnetii, epidemiology, control measures, shedding seroprevalence