Immune responses to foot-and-mouth disease virus in pig farms after the 1997 outbreak in Taiwan.

This paper reports on a retrospective study of the antibody responses to structural and non-structural proteins of FMD virus O Taiwan 97 in six pig herds in Taiwan in the year after the 1997 Taiwanese FMD outbreak. All herds were vaccinated against FMD after the outbreak as part of the countrywide control program. Three of the herds had confirmed FMD infections (herds N, O and P) and three herds remained non-infected (herds K, L and M). The serum neutralizing antibody titers and the non-structural protein ELISA (NSP) antibody responses in sows and 1-month-old pigs in the infected herds were higher than in the non-infected herds, but over time a number of positive NSP reactors were detected. From the serological studies and the herd monitoring and investigations it was considered that the FMD NSP positive reactors may not have constituted a true reservoir of FMD virus infection especially in herds where susceptible pigs were no longer present post-exposure or post-vaccination. Pigs vaccinated with an unpurified FMD type O vaccines being used at that time also showed false positive responses for NSP antibodies.