A passive hemagglutination test has been developed to detect and measure foot-and-mouth disease virus (FMDV) antibody by using glutaraldehyde as a coupling reagent. An optimal concentration of 10 to 40 μg of virus per ml with 0.25% glutaraldehyde at 25 C for 1 hr was established for the sensitization of sheep erythrocytes. A reaction time of 18 hr at 4 C or 2 hr at 37 C induced good agglutination in the presence of specific antibody. Sensitization was carried out in phosphate buffer, whereas agglutination and preadsorption of nonspecific agglutinins from sera were performed in gelatin (0.1%, w/v)-stabilized, phosphate-buffered saline. An optimal pH of 7.2 was also established for all reactions. Antibodies derived from guinea pigs hyperimmunized by infecting with FMDV, types A, O, and C were both virus-and type-specific. Preliminary experiments showed that strain A-119 and strain A-24 Cruzeiro could also be distinguished by hemagglutination. Parallel hemagglutination and complement-fixation tests showed the former to be two to four times more sensitive than the latter.
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