Analytical evaluation of an immunomagnetic separation PCR assay to detect pathogenic Leptospira in cattle urine samples obtained under field conditions.

Clinical manifestations of leptospirosis are diverse and very similar to other febrile diseases, hence early and accurate detection of subclinical infections is a key element in disease control. We evaluated immunomagnetic separation (IMS) capture technology coupled with a standard quantitative PCR (qPCR) system for the detection of pathogenic Leptospira in urine samples from 803 cows from dairy herds with a history of clinical cases of leptospirosis. The urine samples were first processed in a purification step, then subdivided into 2 subsamples, one that continued to DNA extraction and direct qPCR, and one that was pretreated by IMS before continuing to DNA extraction and qPCR. Overall, 133 of 803 (16.6%) samples were IMS-qPCR positive, whereas only 92 of 803 (11.5%) were positive when using direct qPCR. Statistically significant differences were observed between the mean estimated Leptospira load between the IMS-qPCR and the direct qPCR positive urine samples. The IMS-qPCR technology revealed a larger number of positive results and higher bacterial loads than direct qPCR. This difference is most likely the result of the high antigen-binding capacity and capture efficiency of the IMS system. The use of polyclonal antibodies produced by the inoculation of 3 synthetic peptides, which make up the extracellular regions of the LipL32 protein, provided a high detection capacity to the IMS-qPCR technique, resulting in performance superior to direct qPCR.