Kinetics of Coxiella burnetii excretion in a commercial dairy sheep flock after treatment with oxytetracycline

The kinetics of Coxiella burnetii excretion were studied in dairy sheep using a flock that had a previous history of abortion and a positive polymerase chain reaction (PCR) test for C. burnetii in milk from the bulk-tank. An ELISA used to test sera antibodies revealed a high within-flock seroprevalence (54%). Fifty individual milk samples analysed by PCR showed a high number of milk shedders in the flock (38%). In the following breeding cycle, 75% of the animals in the flock were double treated with oxytetracycline (OTC) at days +100 and +120 of gestation, while the remaining 25% of the animals were kept as untreated controls. The percentage of shedders at lambing was similar between groups. Of the treated ewes, 82% shed the bacteria in their vaginal fluids vs. 72% of the untreated ewes. Shedding was also high in faeces (61% of treated vs. 77% of untreated ewes) and milk (57% of treated vs. 50% of untreated ewes). At 2 and 6 weeks later, treated animals continued shedding the bacteria and there were no significant differences in the number of shedders between treated and control groups. Moreover, the bacteria were excreted in faeces for 5 months after parturition, for 3 months in vaginal discharges and for 4 months in milk, which suggested that OTC treatment neither prevented the shedding of bacteria, nor limited the duration of bacterial excretion.