Effects of Selected Adjuvants on Immunogenicity and Protectivity of Pasteurella multocida Bacterin Vaccine in Chickens

Avian pasteurellosis (fowl cholera) is an important disease affecting domestic and wild birds all over the world. Although the capsular type A of Pasteurella multocida is mostly involved, other capsular types are occasionally incriminated. The present study aimed at investigating the effect of some adjuvants on immunogenicity and protectivity of P. multocida bacterin in chickens, compared to an Iranian commercial vaccine. Eight-week-old chicken pullets were double vaccinated with an interval of three weeks. Vaccine immunogenicity testing was conducted using an in-house indirect enzyme-linked immunosorbent assay and assessing serum antibody titers at 7, 14, and 21 days post-primary and 14 days post-secondary immunization. The possible adverse effects were recorded by a poultry-disease expert. For evaluating the vaccine protection rate, chickens were subjected to 2×Lethal Dose 50%of a virulent P. multocida strain two weeks post-secondary immunization. The rate of live and normal animals was regarded as protection rate 7days after the exposure. The findings showed that oil adjuvants Montanide ISA 70-and Montanide ISA 71-containingvaccines (with or without saponin) caused a powerful immune reaction than the aluminum adjuvanted vaccine and commercial vaccine (P<0.05). Significant protection against challenge was merely induced by the oil adjuvanted vaccines (P<0.05). The majority of the studied chickens showed inflammation at the injection site (yellow) throughout the trial. Vaccines made by Montanide ISA 70 and Montanide ISA 71 are novel and effective inactivated vaccines that are able to cause significant protection to fowl cholera disease.