Serologic Profiles of Classical Swine Fever Vaccinated Backyard Pig Farms in Khon Kaen Province, Thailand

Small and marginal farmers with low livestock holdings do not strictly follow recommended vaccination schedules and procedures. The aim of this study was to follow antibody titers against Classical Swine Fever (CSF) virus before and after vaccination of cross-bred pigs from three farms in Khon Kaen. One dose of vaccine was given to the pigs at 41, 49, and 52 days age. It is a modified lived vaccine containing 10² PD₅₀ (50% protective dose) of the CSF virus (government produced Lapinized Chinese-strain, Department of Livestock Disease, Thailand). Blood samples were collected at 0, 14, and 22 days post-vaccination (dpv). Neutralization test was performed in cell cultures using a constant-virus/varying-serum method. In Pigs born to sows that had been vaccinated once a year, geometric mean titers at 0 dpv of 41, 49, and 52 days old pigs were 2.05, 1.24, and 0.72, respectively. The lowest/highest maternal antibody titers were 1: 32/1: 512, 1: 8/1: 64, 1: 2/1: 16, the median titers were 1: 32, 1: 16, and 1: 8, in farms 1, 2, and 3, respectively. At 14 dpv, SN antibody titres of pigs in farm 1 decreased but that of farm 3 increased. Consequently, SN antibody titers of pigs in farms 2 and 3 increased after vaccination and had GMT of 1.82 and 1.09 (p<0.05) at 22 dpv, respectively. General vaccination guideline is not applicable to all farms. Higher SN titers at the day of first vaccination impeded antibody response (14 days old). However, the lowest titer (1: 8) and the oldest pigs (52 days old) did not have the best SN titer after CSF vaccination. There should be laboratory confirmations of CSF antibody titers before and after vaccination in order to assure successful outcome of vaccination practice.