Introduction.

An ELISA test has been developed on the IDEXX SNAP^TM device to detect antibodies to Mycobacterium avium subsp. paratuberculosis (M.pt.), the causative organism of Johne's disease in ruminants. Initial validation studies have been completed utilizing bovine serum as the specimen type. This SNAP test format has potential applications as in-clinic assay for large animal veterinarians who require a rapid test result (22') for symptomatic or suspicious animals. The purpose of the study in this report was to evaluate the performance of this new M. pt. ELISA by testing populations of dairy cattle (n = 1276).

Materials and Methods.

Sera were tested with the prototype test system and with a USDA-licensed microtiter plate antibody test kit. Quantitative data were recorded for the SNAP test platform by taking densitometric readings of the diagnostic spot at the completion of the test protocol. These values were compared to the S/P ratios yielded by the microtiter-plate technique by regression analysis.

Results.

The percent agreement in test results between the two assay methods utilized for herd groups defined by test histories were as follows: known infected herds - 94.4%; presumed negative herds - 99.1%; herds of unknown status - 96.8%. Regression analysis of quantitative data shows a significant correlation between the two techniques utilized, (R2 = 0.73; p < 0.0001; 95% CI). Ninety-six point six percent (96.6%) of the sera tested (1232 of 1276) yielded an agreement in serologic status as determined by the two test methods evaluated.

Conclusions.

The relative sensitivity and specificity of a new ELISA test was measured against an established technique. These data provide evidence of a significant correlation in performance between the new SNAP test and the microtiter-plate format. Further, the prototype SNAP test yields specimen dispositions which are consistent with the known source-herd histories for the bovine populations studied.