Serologic monitoring of herds with and without bacterin vaccination for Actinobacillus pleuropneumoniae

Objective: Investigate diagnostic serology for Actinobacillus pleuropneumoniae (APP) infections in naturally infected and vaccinated pigs. Materials and methods: The APP status of 12 farms (A-L) was established by lung cultures and isolate serotyping. Screening enzyme-linked immunosorbent assay (ELISA) detected antibodies to ApxIV antigen or multiple APP serotypes. Serotype-specific ELISAs were conducted for serotypes 5 and 7. Seven groups of farm F pigs (serotype 7) were moved to farm K (serotype 5). Autogenous vaccines (V1/V2) prepared from APP serotype 5 cultures from farm K and a commercial, killed APP vaccine (V3) containing serotypes 1, 7, and 15 were used to vaccinate pigs in each group twice or thrice at 3-week intervals, commencing at 10 weeks of age. Blood samples were analyzed with ELISAs specific for serotype 5 and ApxI and ApxII toxins. Serum titers were compared using an analysis of variance. Results: Serotypes 5, 7, 12, or 15 were present in lung cultures. The ApxIV screening ELISA and mix-serotype ELISA regularly detected serotypes 5, 7, and 15. Serotype 12 infections were detected in the mix-serotype ELISA, but not in the ApxIV assays. The serotype 5 or 7 specific ELISA regularly detected herd infections with the relevant serotype. Serotype 5 titers of pigs vaccinated with V1/V2 thrice were higher than those dosed twice with the equivalent volume (P < .05). Pigs receiving V3 showed no serotype 5 antibody response. The ApxI and II titers in V1/V2-vaccinated pigs were higher than controls. Implications: Screening and serotype-specific ELISAs verified APP status. Repeated serotype-specific autogenous APP vaccine doses provided a strong antibody response.