Abstract
Protective effect of an inactivated Al (OH)3 gel-absorbed vaccine prepared from Haemophilus pleuropneumoniae (Hpn) serotype 2 strains was investigated. About 80% of the pigs injected intramuscularly with the Hpn vaccine survived the intratracheal challenge with the homologous strain. Localized hemorrhagic lesions were observed in the lungs of the surviving pigs. From the lesions, a few organisms were constantly recovered. No septicemia was observed in these pigs. In contrast, severe hemorrhagic lesions were observed in the lungs of all the dead pigs, and numerous organisms were recovered from the lung, the heart blood, and the peritoneal fluid. The Hpn vaccine was effective to prevent the death caused by Hpn septicemia, and the protective potency of the vaccine can be estimated by the surviving rate of the injected pigs. Since the level of the complement-fixation (CF) antibody titers significantly correlated to the protection rate defined by the surviving rate, the CF test might be applicable for evaluating the protective potency of the Hpn vaccine.
