PROTECTIVE EFFICACY OF CONJUGATE VACCINES AGAINST EXPERIMENTAL CHALLENGE WITH PORCINE ACTINOBACILLUS-PLEUROPNEUMONIAE

In an attempt to protect pigs against swine pleuropneumonia induced by Actinobacillus pleuropneumoniae (SPAP) by neutralizing the effects of three virulence factors of A. pleuropneumoniae - the capsular polysaccharide (CP), the lipopolysaccharide (LPS), and the hemolysin protein (HP) - two subunit conjugate vaccines were prepared by covalently coupling the CP to the HP and the LPS to the HP. The CP, LPS, and HP were isolated from A. pleuropneumoniae, strain 4074, serotype 1, and the protective efficacy of the conjugate vaccines in swine experimentally infected with A. pleuropneumoniae was evaluated. Following a booster vaccination, a significant (P<0.05) IgG antibody response to the CP, LPS, and HP was detected in the vaccinated pigs. The pigs vaccinated with the CP-HP and LPS-HP conjugates exhibited significantly less mortality (P<0.05) and significantly greater weight gain (P<0.001) than unvaccinated pigs. Vaccinated pigs exhibited significantly fewer and less extensive gross pulmonary lesions (P<0.001) when compared with unvaccinated pigs. Thus, on the basis of mortality, weight pins, and pulmonary lesion formation, the two conjugate vaccines used in conjunction with one another provide noticeable protective efficacy against SPAP.