Comparative between-laboratory trials of the liquid-phase blocking sandwich ELISA for the detection of antibodies to foot-and-mouth disease virus.

Fifty bovine serum samples were tested for the presence or amounts of antibodies to foot-and-mouth disease (FMD) virus serotypes A, O and C by the liquid-phase blocking sandwich ELISA (lpb-ELISA) using reagents prepared by the World Reference Laboratory for Foot-and-Mouth Disease (WRL) in Pirbright, U.K. Twenty of the sera had been collected before extensive vaccination with a commercial inactivated trivalent FMD vaccine was ceased and the remaining thirty originated from animals which had not been vaccinated for more than one year. After the test had been completed, the samples were sent to another two laboratories to be examined by the same assay. Results obtained in the laboratories were compared to assess the degree of agreement in serological tests for FMD in cattle. Antibodies to at least one of the three FMD virus (FMDV) serotypes were demonstrated in 70% of the serum samples. Antibodies to the antigens A5, O1 and C1 were present in 58%, 66% and 58% of the sera, respectively. The overall between-laboratory agreement of the results of the lpb-ELISA for the detection of antibodies against all three serotypes was 96%. Discrepancies in terms of type specificity did not exceed 10%. Most discrepancies were recorded in sera with low antibody titres or optical densities (OD) around the cut-off point. An increase of concentration of C1 antigen in reaction mixture reduced the sensitivity of ELISA and results of screening tests became negative in sera with antibody titres of 1: 90 and lower.(ABSTRACT TRUNCATED AT 250 WORDS)