Evaluation of the efficacy of oxytetracycline treatment followed by vaccination against Q fever in a highly infected sheep flock.

The aim of this research was to evaluate the efficacy of oxytetracycline treatment following an outbreak of Q fever in a sheep flock when gestation is too advanced for vaccination to be used. In such cases, immediate application of antibiotics is needed and vaccination postponed until the next breeding season. Seventy-five per cent of ewes from a dairy sheep flock affected by Q fever were treated with oxytetracycline at approximately days 100 and 120 of gestation, with the remaining 25% of the animals kept as untreated controls. Vaginal swabs, faeces and milk samples from 81 ewes (57 treated, 24 untreated) were analysed by PCR within 30 days of lambing and revealed a high percentage of Coxiella burnetii shedders. No significant differences were found between groups in either the percentage of shedders or in the mean amount of bacteria shed. In the following season 75% of the ewes and 50% of the replacement ewe lambs were vaccinated with a phase I vaccine prior to artificial insemination. Both vaccinated and control groups were homogeneously composed of ewes treated and untreated with antibiotics in the previous season. The number of shedders and the bacterial excretion load decreased significantly compared to the previous season but no statistically significant differences were found between vaccinated and control groups. In addition, no significant effect derived from the application of oxytetracycline in the previous season was observed. Vaccination was repeated for the following two seasons, and the percentage of animal shedders was reduced to minimal levels highlighting the importance of vaccination over the longer term.