Protective efficacy of an affinity-purified hemolysin vaccine against experimental swine pleuropneumonia.

Protective efficacy of Actinobacillus pleuropneumoniae extracellular hemolytic toxins, RTX-toxin I (Apx I) and Apx II, was evaluated in pigs. The hemolysins were purified from culture supernatant of A. pleuropneumoniae strain HA-337, serotype 1 by immunoaffinity chromatography using a monoclonal antibody specific for Apx I or Apx II as ligand. Four pigs were vaccinated with the purified hemolysins absorbed on aluminum phosphate gel adjuvant. Four pigs of a control group were given placebo. Hemolysin-neutralizing antibodies were detected only in vaccinated group after booster injection. One of four control pigs died following an aerosol challenge with the homologous strain, and three surviving pigs developed serious clinical signs of pneumonia and had extensive lung lesions. In contrast, there was no mortality in vaccinated group. Only transient hyperthermia was observed in two vaccinated pigs after challenge. A necropsy, two vaccinated pigs had slight localized pulmonary lesions, though the remaining two had no lung lesions at all. These results indicate that the hemolysin vaccine made of Apx I and Apx II has good protective activity against swine pleuropneumonia caused by A. pleuropneumoniae serotype.