Experimental vaccination of pigs with an Actinobacillus pleuropneumoniae serotype 5b capsular polysaccharide-tetanus toxoid conjugate.

The protective efficacy of an Actinobacillus pleuropneumoniae serotype 5b capsular polysaccharide-tetanus toxoid conjugate (Ap5bCP-TT) against homologous challenge of pigs was investigated. Four pigs were non-vaccinated controls (group A), 4 pigs were injected with adjuvant without antigen (group B) and 8 pigs were vaccinated with Ap5bCP-TT and adjuvant (group C). Pigs vaccinated with Ap5bCP-TT developed antibody responses to the capsular polysaccharide from A. pleuropneumoniae serotype 5b (Ap5bCP). After challenge, all pigs in groups A and B had severe clinical signs of disease and were euthanized. In group C, 3 out of 8 pigs showed severe symptoms and were euthanized. Five pigs in group C survived throughout the study. The post challenge observation period was 72 h. All pigs were subject to necropsy and results from gross pathological findings and microbiological examination are described. Pigs vaccinated with Ap5bCP-TT had statistically significant reduced values of the mass ratio of affected to unaffected lung tissue compared to pigs in groups A and B (p = 0.01 and p = 0.007, respectively). The results showed that Ap5bCP-TT-vaccination had considerable protective efficacy against lethality and pulmonary lesions caused by experimental infection with A. pleuropneumoniae serotype 5b.