COMPARISON OF A 3ABC ELISAANDTHE LIQUID-PHASE BLOCKING ELISA OF FOOT-AND-MOUTH DISEASE IN AN AREA OF ENDEMICITY

摘要

The performance of a modified liquid-phase blocking ELISA (LPBE) that revealed wide sEroprEvalence of type "A" and "SAT2", than previously reported, in non-vaccinated Sudanese cattle was compared with a 3ABC ELISA. Neither non-specific reactions nor discrepancy could be monitored. Excluding one serum, none of the 3ABC negative or borderline sera (n= 19) showed significant positive reaction to any of both types in the LPBE, and all of them were negative for the moderately prevalent type "SAT2". All 3ABC positive sera (n=54) were positive for the predominant type "A" except two sera while only 57 of them (n=44) were positive for type "SAT2". in distinct test groups, increase of sEroprEvalence in the three test systems (3ABC, type "A" and type "SAT2"ELISAs) was concurrent.At the level of individual animals, the higher the PP of a given serum in 3ABC,the more likely it was positive to both types in the LPBE. Sera with higher positivity range values to 3ABC polyproteins showed higher average positivity values to SPs of both types. Good correlation between results of the two tests gave credibility to both of them.In the test group, the predominance of type "A" (infection) antibody (88) was distinguished from the medium prevalence (infection) of type "SAT2" (41 ) by good correlation between the increase in positivity range values to SPs of the former, not the latter, with the positivity averages to 3ABC polyproteins.Among type "A" positive sera, highest positivity did not match that of 3ABC, while among type "SAT2" positive sera, highest positivity matched that of 3ABC distinguishing the likely repeated infection with the predominant type from the recent infection of juvenile cattle (fully susceptible to serotype "SAT2") with the medium prevalent one.When discrimination of sera as positive or negative in the 3ABC test (not serotype specific) and the most predominant type "A" ELISA was compared, 76 of results were concordant and 24 were discordantThese figures are comparable to those obtained when comparing the performance of a competitive 3ABC ELISA with a combined virus neutralization test, as the "gold standard", in an area of endemicity. Almost the whole of the discordant results were negative or borderline cases for anti-3ABC antibodies that were marginally positive for anti-SP antibodies, likely because of different duration of antibody.