ASSESSMENT USING ELISA OF THE HERD-IMMUNITY LEVELS INDUCED IN CATTLE BY FOOT-AND-MOUTH-DISEASE OIL VACCINES

The development of a liquid-phase blocking sandwich ELISA (LPBE) to me asure antibodies (Ab) produced in cattle with the O, A and C foot-and- mouth disease virus (FMDV) types of commercial vaccines used in Argent ina is described. The test was specific: 99% of naive cattle sera (n = 130) gave titres below log(10) = 1.2, and none had a titre above log( 10) = 1.5, Comparative studies with serum neutralization test (SNT) us ing sera from cattle which received one or more vaccine doses is repor ted. The overall rank correlation coefficient (Spearman's rho, r(s)) b etween SNT and LPBE were highly significant (r(s) > 0.67, P < 0.0001) for all vaccine strains. LBPE Ab titres on sera collected 90 days post vaccination were compared with results of cattle protection tests by applying a logistic regression. The minimum Ab titres at which 85% and 75% of the cattle were protected for each FMDV type were determined i n order to interpret field Ab data in terms of protection. Application of this method allows large scale serological examinations to monitor antibody levels in vaccinated animals as an indirect indicator of the FMD control program status in the field. Its use in the evaluation of commercial batches of FMD vaccine is discussed. (C) 1998 Elsevier Sci ence B.V.