ISCOM ELISA in milk as screeningb for Neospora caninum in dairy sheep.

Introduction - Neospora caninum is recognized as one of the major causes of abortion in cattle and as a causative agent of reproductive disorders in sheep. Aims - To assess if milk can be used as a matrix for serological investigations of N. caninum in sheep, in the same way as that performed for blood serum, and then to perform an epidemiological survey using bulk tank milk from various sheep farms located in Sardinia (Italy). Materials and methods - In the first step, individual blood and milk samples of 304 sheep from 5 different farms were tested using a commercial ISCOM ELISA kit. Samples with a Percent Positivity Value (PP%) ≥ 20 were considered positive. In a second step an epidemiological survey was carried out on bulk milk samples collected from 613 sheep farms in Sardinia. Results and discussion - Antibodies against N. caninum were detected in all of the 5 monitored farms, with positivity of 44.4% and 46.4% in blood and milk samples respectively. Statistical analysis of the results showed a good correlation between blood and milk samples (r = 0.946; P < 0.001). A TG-ROC plot allowed us to establish that the optimal cut-off for milk analysis was 20.04 PP%. The epidemiological survey on bulk tank milk revealed the presence of a high quantity (PP% ≥ 20) of antibodies against N. caninum in the 44.2% (271/613) of farms examined. The present work represents the first sero-epidemiological survey of N. caninum carried out in dairy sheep milk. Sensitivity and specificity obtained with ISCOM ELISA on milk compared with blood serum, indicated that milk from individuals can be a useful tool for large-scale seroepidemiological surveys of N. caninum. Conclusions - The high level of antibodies against the protozoa found in the bulk milk analyzed suggests that further studies are necessary to assess the best cut-off for analysis of this kind of sample and to understand better the parasitic dynamics in this small ruminant.