Some observations on the comparative performance of two 3-ABC eELISAs in an area of endemicity
The performance of Chekit and Priocheck (Ceditest) 3-ABC ELISAs was evaluated in an area of endemicity using 196 sheep and 45 bovine sera. The Checkit ELISA failed to detect 8 positive sheep sera out of 10 detected by the Priocheck ELISA whilst both ELISAs detected 13 bovine sera as positive or borderline. The dissimilarity in the performance of the two ELISAs in testing sheep field sera, a target population, was shown to be consistent with their reported differences following experimental infection in cattle and was largely due to differences in their methodology. Sera expected to form high affinity and small immune complexes are better detected in the system of Priocheck-NS blocking ELISA while sera expected to form low affinity (recent infection) and large immune complexes are better detected in the latter system of Chekit ELISA. Identification of this aspect is crucial for optimization of these assays and for conclusive interpretation of their results. Prevalence in the test sheep group as detected by the Priocheck ELISA (8.47%) was more pertinent to the expected true prevalence than that detected by the Checkit ELISA (0.51%). The Checkit ELISA could prove to be useful for detection of relatively recent FMD virus circulation and, hence, control plans in enzootic areas.
Key words: Foot-and-mouth disease; 3-ABC serology; Ceditest; Priocheck: Chekit ELISA; Blocking ELISA