COMPARISON OF FOOT-AND-MOUTH-DISEASE VIRUS ASIA-1 FIELD ISOLATES AND VACCINE VIRUS BY PLAQUE-ASSAY AND PLAQUE REDUCTION NEUTRALIZATION TEST

Two field isolates of type 'Asia 1' foot-and-mouth disease virus (FMDV ) were compared with the homologous vaccine strain virus by plaque ass ay and plaque reduction-neutralization (PRN) test. The size of the pla ques formed by the vaccine strain virus and the field isolates varied from 2-5 mm in diameter. In PRN test, the dilutions of anti-1465 guine apig serum (raised against the vaccine strain; virus) causing 70% redu ction in the number of plaques were round to be 870.40 (+/-5.83), 409. 60 (+/-1.83), and 358.40 (+/-1.53) for the vaccine strain virus and th e two field isolates, respectively. This showed that the vaccine strai n virus required lesser amount of antibodies than the two field isolat es in causing 70% reduction in the number of plaques. However, the pla que reduction curves of these two field isolates showed no difference from that of the vaccine strain virus.