Host responses and bacterial colonization following inoculation of Pasteurella multocida P 52 strain into unvaccinated and aluminum hydroxide gel hemorrhagic septicemia vaccinated mice.

Hemorrhagic septicemia is a highly infectious and contagious disease caused by Pasteurella multocida serogroup B:2 in tropical Asian and African countries. The acute inflammatory responses induced by Pasteurella multocida are the main cause of death in hemorrhagic septicemia. Therefore, present study was undertaken to examine the blood cytokine expression profiles (TNF-α, IL-1β, and IL-6), bacterial colonization and histopathological changes of intraperitoneally and subcutaneously challenged vaccinated and unvaccinated mice with 102  CFU of P. multocida P52 . The observations were made at 6, 12, 18, 24 h and 48 h intervals. Real-time PCR based blood cytokine profiles (TNF-α, IL-1β, and IL-6) measurement revealed a significantly higher amount of pro-inflammatory cytokines expression in the unvaccinated challenged group of mice than the vaccinated challenged group. There was heavy bacterial load in all organs of mice viz. trachea, lung, spleen, within 6 h of challenge in both vaccinated and unvaccinated group of mice, but bacterial load increased in the unvaccinated challenged group of mice with respect to time whereas the load were constant in the vaccinated challenged group. Histopathological changes were mild in the vaccinated challenged group of mice in comparison to the unvaccinated challenged group. There was no significant difference in the bacterial load, histopathological changes and cytokines expression when challenged through different routes.