Development of an experimental animal model for the protection test of Haemophilus pleuropneumoniae vaccine.

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Abstract
Protective effect of an inactivated vaccine prepared from Haemophilus pleuropneumoniae (Hpn) serotype 2 strains was investigated. About 80% of the guinea pigs injected intramuscularly with the Hpn vaccines survived the intraperitoneal (IP) or intratracheal (IT) challenge exposure with the homologous strains. The survived animals had at least 1:16 of the complement-fixation (CF) antibody titers. The challenge-exposed organisms were completely cleared from the various tissues and organs of the survivals, and their lungs appeared to be normal. In contrast, all the dead guinea pigs which had less than 1:16 of the CF titers showed severe extensive hemorrhagic lesions in the lungs, and numerous organisms were recovered from the lung, the heart blood, and the peritoneal fluid of each dead guinea pig. Protective potency of the Hpn vaccine could be estimated by the surviving rate of the injected guinea pigs, in addition to this, the protection rate significantly correlated to the level of the CF antibody titers. There were no differences in protection rate either among the 5 challenge strains or between the IP and IT exposure routes. Guinea pigs, instead of pigs, might possibly be applicable as a suitable experimental model for evaluating protective potency of the Hpn vaccine.