Study On The Solid-phase Competition ELISA For Measuring Antibody To Foot-and-mouth Disease Virus Type Asia-â… 

A solid-phase competition ELISA (SPCE) has been developed to measure antibodies to foot-and-mouth disease (FMD) virus and has been validated using an extensive range of sera from cattle. In this study, the SPCE method for detecting antibodies against FMD type Asia-I was established using the field prevalent strains in our country and referring to the OIE's standard method in our laboratory,by which the research of application also was finished by the numbers.To evaluate the performance of the test,213 FMD negative sera and 70 FMD positive sera detected with SPCE (background test) for defining the cut-off of the assay. The results were analyzed in terms of percentage inhibition at each dilution,the dilution at which there was optimal differentiation of positive from negative sera was 1:32. At this dilution there was no overlap in the two populations. All positive sera had more than 40% inhibition and all negative sera less than this value. It can be confirmed that a cut-off value of 40% inhibition at 1:32 dilution was optimal for differentiating positive from negative sera. On the basis of the background test and standard differences, it was confirmed that the reaction consult would be positive as the antibody titer was larger than 1:40 in SPCE, negative as less than 1:25, suspect as between 1:25 to 1:40.Having established a provisional cut-off for the test, large numbers of serum were then examined. Through measurement of 30 bovine sera positive for FMD, it was shown that the correlation coefficient between SPCE and LPB-ELISA was 0.9, between SPCE and VNT was 0.72, which were regarded as high degree correlation. A indicatrix of the assay was analyzed by the analytical sensitivity and the specificity,140 FMD sera from vaccinated animals,5 FMD sera from infected,51 FMD sera obtained from cattle between 21 and 28 days after either infection or vaccination with single, defined strains of FMD virus of known origin and 310 FMD negative sera and. All of serums were used to compare the sensitivity and the specificity of the assay. It was revealed that the sensitivity of SPCE and LPB-ELISA was 96%,97%, the specificity of SPCE and LPB-ELISA were 98%,100%, respectively. The result of across reaction tests showed that no across reactions of the antigens of FMDV type Asia-I with sera positive for FMD type O, or Asia-I , type O in abroad, or with serum positive for swine vesicular disease. The result of using SPCE and LPB-ELISA to measure 95 sera sample revealed the coincidence frequency between SPCE,LPB-ELISA and the liquid-phase blocking of the abroad was 98%. The assay thus retains the sensitivity of LPB-ELISA whilst being easier to use, more robust and specific, and therefore offers an improvement for FMD virus antibody detection.