Performance characteristics and optimisation of cut-off values of two enzyme-linked immunosorbent assays for the detection of antibodies to Neospora caninum in the serum of cattle.

AIM: To determine the performance characteristics of two enzyme-linked immunosorbent assays (ELISAs) manufactured by Institut Pourquier (IP) for the detection of antibodies against Neospora caninum in bovine sera. METHODS: Sera from 526 cattle were assayed in two ELISAs (IP) for the detection of anti-N. caninum antibodies. Results from a further ELISA (IDEXX) were used to provide the "gold standard"N. caninum infection status of the cattle and the ELISA results assessed by two-graph receiver operating characteristic (TG-ROC) analysis. RESULTS: TG-ROC analysis suggested changes to one of the IP ELISA protocols, arriving at a cut-off threshold that was different to the one recommended by the manufacturer. With that change, both of the ELISAs performed with high sensitivity and specificity (in excess of 98%) for bovine sera. CONCLUSIONS: The analysis of the two IP ELISAs when used on individual bovine sera demonstrated high sensitivity and specificity. TG-ROC analyses optimised the cut-off point suggested by the manufacturer for one of these commercial diagnostic assays and found agreement with the manufacturer's cut-off regarding the other assay. This will help with the accurate identification of infected animals and thereby contributing to the control of neosporosis.