Gamma Irradiated Pasteurella multocida Vaccine induces strong humoral immunity and protects rabbits from disease

Pasteurella multocida is affecting a multitude of animals and severely affects livestock production. Existing vaccines are mostly chemically inactivated and do not lead to wide protection. Irradiated vaccines are enjoying a renaissance and the concept of "replication defficient but metabolically active" vaccines was recently evaluated in several vaccine trials. P. multocida was isolated from the nasal swab, blood, and lung swab samples from infected rabbits. Gamma irradiation of P. multocida for inhibition of replication was evaluated at an optimized irradiation dose of 10 Kgy established. Four groups of rabbits were (mock) vaccinated with a commercial P. multocida vaccine and three irradiated formulations as liquid, lyophilized formulations with added Trehalose and lyophilized-Trehalose with an "activation" culturing the irradiated bacteria for 24 in broth. Evaluation of humoral immune response by ELISA showed that all three irradiated vaccines produced an effective, protective, and continued IgG serum level after vaccination and bacterial challenge. The IFN-γ expression is maintained at a normal level, within each individual group however, the lyophilized trehalose irradiated vaccine showed peak mean of IFN-γ titer at one week after booster dose (day 21) which was statistically significant. Cumulatively, the results of this study show that gamma-irradiated P. multocida vaccines are safe and protect rabbits against disease. Moreover, Rabbits' immunization with the three irradiated formulations avoided adverse side effects as compared to commercial polyvalent vaccine, the body weight gain for the irradiated vaccine groups indicates less stress compared to the commercial polyvalent vaccine.