Coxiella burnetii Circulation in a Naturally Infected Flock of Sheep: Individual Follow-Up of Antibodies in Serum and Milk

The control of Q fever, a zoonotic disease caused by the Coxiella burnetii bacterium, remains a scientific challenge. Domestic ruminants are considered the main reservoir, shedding C. burnetii essentially through parturition products during abortion or birth. Sheep are particularly frequently associated with human outbreaks, but there are insufficient field data to fully understand disease dynamics and to instigate efficient control measures. A longitudinal follow-up study of a naturally infected sheep flock was performed (i) to investigate relationships between seropositivity and bacterial shedding in the vaginal mucus, (ii) to describe the kinetics of antibodies, including responses to vaccination, (iii) to monitor maternal antibodies in ewe lambs, and (iv) to compare serological results for milk and serum samples. For 8 months, we collected blood samples every 3 weeks from 11 aborting and 26 nonaborting dairy ewes, 20 nonaborting suckler ewes, and 9 ewe lambs. Individual milk samples were also obtained from lactating females. All serum and milk samples were tested by enzyme-linked immunosorbent assay (ELISA), whereas vaginal swabs were tested by quantitative PCR. We found that some dairy females did not seroconvert despite shedding C. burnetii in their vaginal mucus. Overall, antibody levels in adult females were found to remain stable over time, with exceptions during the mating and lambing periods. Maternal antibodies decreased during the first month after birth. Interestingly, antibody levels in milk were correlated with those in serum. This study provides valuable field data that will help improve Q fever surveillance and within-flock management measures.IMPORTANCE Field data are necessary to improve the surveillance, diagnosis, and sanitary management of Q fever in livestock. Here, we provide extensive serological data obtained from serum and milk samples from infected and vaccinated ewes belonging to a naturally infected flock of sheep. We show that antibody levels are stable over time and seropositivity and vaginal shedding are not clearly correlated, whereas antibody levels in milk are strongly correlated with those in serum. Accordingly, we find that antibody levels in bulk tank milk are consistent with the variations observed in the serum of dairy females over time. We report the existence of maternal antibody transmission to ewe lambs and we show that the presence of maternal antibodies at birth does not prevent the development of a serological response to vaccination at the age of 4 months. Finally, we report that adult ewes generally seroconvert after vaccination, including during pregnancy.

The relationship between nasal myiasis and the prevalence of enzootic nasal tumours and the effects of treatment of Oestrus ovis and milk production in dairy ewes of Roquefort cheese area

Infection by Oestrus ovis is common in Lacaune dairy ewes of Roquefort cheese area (Aveyron, France). It is believed by local breeders that there is a close relationship between nasal myiasis and the incidence of enzootic nasal tumour. In order to check these anecdotal reports, a serological survey was done on 658 breeding ewes before turn-out and 897 breeding and primiparous (hoggets) ewes at the end of the grazing season. By the time of sampling, it was clear whether the sheep were infected at the end of the winter or had been re-infected over summer. In April and September, 40.7 and 26.3%, respectively, were free of O. ovis infection, indicating that the autumn treatment was not completely effective and that O. ovis adult flies were circulating during the summer in many flocks. There were no differences in the incidence of adenocarcinoma between the groups indicating that there is no relationship between O. ovis infection and the presence of the cancer. Differences in milk production between the three groups were not statistically significant (Anova test P>0.05). In flocks where 1-5% of the ewes were infected or in non-infected flocks, ewes produced 3.6 and 8.56%, respectively, more milk than ewes from flocks where more than 5% of animals were infected. For primiparous ewes, the differences were of 8.5 and 12.24%.

[Assessing the accuracy of the practice of a method of scoring the body condition of ewes within a professional framework]

The accuracy of the body condition scoring for ewes using lumbar palpation was assessed by mean of an experiment conducted under conditions close to those occurring everyday on the farms. Thirteen operators evaluated the body condition score twice in a sample of 48 Lacaune breed dairy ewes, using a semi-quantitative grid (from 0 to 5 points, with a 0.25 point precision). Under the experimental conditions, the repeatability of the method, i.e. the comparison between the scores given by the same operator to the same animals for the two successive scoring notations, was good and even very good (Kappa test), if a 0.25 point precision is tolerated. On the other hand, the reproducibility, i.e. the comparison between the scores given to the same animals by differents operators was poor. Therefore, this method is easy to master for the management of a given flock by a single person. However in order to make comparisons between flocks, in reference to body condition standards set up for different farming systems, this method needs greater precision. Some of the application conditions required for this are discussed.