Studies on immunity to Haemophilus pleuropneumoniae infections in mice.

A murine model of experimentally induced Haemophilus pleuropneumoniae respiratory tract infections was developed and used to evaluate the efficacy of bacterins. Various doses of 3 H pleuropneumoniae strains (serotype 1 and 5) were administered intranasally (IN) to groups of anesthetized Swiss White mice. The accumulated mortality per group at 5 days after they were inoculated was used to calculate the median lethal dose (LD50), which ranged between 1.4 x 10(6) and 5.4 x 10(7) bacteria. There was correlation between dose administered, incubation period of the disease, and mortality. The induction of H pleuropneumoniae disease in the mouse was reproducible and resembled that of naturally occurring porcine Haemophilus pleuropneumonia. The murine model of exposure was used to evaluate the efficacy of H pleuropneumoniae serotype 5 (strain B78-3760) bacterins administered subcutaneously (SC) and IN. Vaccination by SC route induced slightly higher titers of specific seroagglutinins, compared with the response induced by the IN route, and the former was more effective in protecting mice against IN challenge with H pleuropneumoniae. However, vaccination was not efficacious in mice given a challenge dose greater than 1.2 LD50. The percentage survival rates in the SC and IN vaccinated mice were significantly greater than in the control groups at P less than 0.01 and P less than 0.05, respectively.