Estimation of Coxiella burnetii prevalence in dairy cattle in intensive systems by serological and molecular analyses of bulk-tank milk samples.

A large-scale investigation on Coxiella burnetii was carried out in dairy cattle herds from a Q fever-endemic region to evaluate the degree of exposure to C. burnetii and to estimate prevalences. This study included all of the dairy cattle herds from the province of Bizkaia, Northern Spain (n=178). Herds were visited between September 2009 and February 2010, and 100mL of bulk-tank milk (BTM) per farm was collected to be analyzed by ELISA and PCR. Blood samples were also taken from about 15 animals randomly selected from each herd. One hundred nineteen of the 178 studied herds (66.9±6.9%) were positive for the presence of anti-C. burnetii antibodies in BTM. Serum samples from 1,306 cows, 654 heifers, and 502 calves were analyzed by ELISA, and cows showed a statistically significantly higher seroprevalence (12.3±1.8%) than heifers (1.1±0.8%) and calves (0.0±0.0%). Eighty-nine herds (50.0±7.3%) had at least 1 seropositive animal, but within-herd prevalences higher than 20% were only observed in 24 herds (13.5±5.0%). A significant correlation was observed between BTM ELISA sample-to-positive control ratios and within-herd seroprevalence, being higher when considering only cows (R(2)=0.21). Animals from herds with negative BTM by ELISA showed a mean seroprevalence of 2.5%, whereas animals from herds with positive BTM samples had a statistically significantly higher seroprevalence (8.9%, F=19.7, degrees of freedom=1). The proportion of herds C. burnetii positive by BTM PCR was 51.7±7.3% (92/178). The widespread distribution of C. burnetii in cattle advocates for the implementation of Q fever control strategies.

Measuring antibody levels in bulk-tank milk as an epidemiological tool to search for the status of Coxiella burnetii in dairy sheep.

Pooling samples may provide a valuable alternative to individual testing for pathogen surveillance purposes. We studied the reliability of measuring the level of antibodies against Coxiella burnetii in bulk-tank milk (BTM) to estimate the seroprevalence of C. burnetii in dairy sheep in 34 flocks. We then estimated the seroprevalence of C. burnetii in 154 dairy sheep flocks according to the level of antibodies in BTM. We tested for the accuracy of our estimation at the population level by comparing predicted mean C. burnetii flock seroprevalence with that obtained in another survey performed on the same population. Our findings showed that testing BTM by ELISA is a cost-effective and relatively good index of the seroprevalence of C. burnetii in dairy sheep and may be a useful tool for epidemiological surveillance at the population level.

Molecular investigation of the occurrence of Coxiella burnetii in wildlife and ticks in an endemic area.

At present few studies have been carried out on the distribution and incidence of Coxiella burnetii infection in wildlife. Therefore, the aim of this study was to investigate the distribution of C. burnetii in the main wild species in the Basque Country (Northern Spain), such as carnivores, cervids, wild boar, lagomorphs and several species of birds. Tissues from a total of 601 animals and 340 adult ticks collected from them were analyzed by PCR. DNA of C. burnetii was detected in 5.1% of roe deer (Capreolus capreolus), 4.3% of wild boar (Sus scrofa), 9.1% of European hare (Lepus europaeus), and among wild birds, in 11% of vultures (Gyps fulvus) and 14% of black kites (Milvus migrans). These results showed that C. burnetii circulates in wildlife in Spain participating in the cycle of Q fever in nature. All of the adult ticks analyzed were negative for C. burnetii, suggesting that ticks do not play an important role in the transmission of C. burnetii in this area.

Coxiella burnetii shedding and environmental contamination at lambing in two highly naturally-infected dairy sheep flocks after vaccination.

Abortion due to Coxiella burnetii was confirmed in the 2007/08 season in two naturally-infected dairy sheep flocks. Proportion of C. burnetii shedders and bacterial loads in vaginal mucus were high among aborted or lambed ewes, as was within-flock seroprevalence. Before the next reproductive season (2008/09) 75% of ewes and 50% of replacement lambs were vaccinated (Coxevac, CEVA Santé Animale) keeping the remaining as untreated controls. Compared with the previous year results when abortion outbreak started, a great reduction in the percentage of abortions, in the number of shedders and in the bacterial burden excreted by the ewes was found in both flocks. However, seroconversion in non-vaccinated yearlings from both flocks and the presence of C. burnetii DNA in bioaerosols taken at sheep premises at lambing indicated that infection was still active. No differences were observed between vaccinated and control groups in terms of proportion of C. burnetii shedders. These results suggest that optimal results of vaccination in heavily infected flocks may not be obtained in a short-term period.

Short communication: investigation of Coxiella burnetii occurrence in dairy sheep flocks by bulk-tank milk analysis and antibody level determination.

To estimate the prevalence of Coxiella burnetii in the dairy sheep population from the Basque Country (northern Spain), a study was carried out combining molecular and serological techniques. First, bulk-tank milk samples from 154 flocks belonging to the Latxa Breed Farmers Association were analyzed by PCR, with 22% of flocks testing positive for C. burnetii. Then, a selection of 34 flocks (7 PCR positive and 17 negative) was investigated for the presence of serum antibodies by ELISA test on 1,011 ewes (approximately 30 ewes per flock). A total of 8.9% of the animals were seropositive, 67.6% of the flocks had at least one seropositive animal, but only in 14.7% of them was seroprevalence greater than 25%. Older ewes showed a significantly greater prevalence (17.5%) compared with yearlings (7.5%) or replacement lambs (1.5%). A marginally significant association was found between seroprevalence and PCR detection of C. burnetii in bulk-tank milk. The widespread distribution of C. burnetii in the region advocates for the implementation of Q fever control strategies and highlights the potential risk of sheep as a reservoir and infection source for other domestic and wildlife species and the human population.