Standardization and development of Pasteurella multocida inactivated adjuvanted vaccine against septic pasteurellosis in pigs

In piggery, septic pasteurellosis caused by Pasteurella multocida (B:2) is an issue of concern, which needs an effective vaccine. Here, we prepared a double emulsified (DE) vaccine containing 2.5 mg inactivated antigenic mass of pig field strain (B:2) (named as soron) isolated from an outbreak of septicaemic death in pigs and P. multocida P-52 cattle strain (B:2) and studied their efficiency in terms of immunity to direct challenge, duration of immunity and the role of humoral and cell-mediated immunity. Both of these strains showed presence of hgbB, pfhA, nanH, ptfA, and tbPA virulence genes. The sequence analysis of bands of 760 bp product using capsular primers were obtained for soron and P-52 revealed 99.2% homology between these two strains, indicating differences at genetic level. nanH and pfhA genes of soron shared 99.2% and 92.7% homology with P-52, respectively suggesting differences between these two strains at genetic level. SDS-PAGE analysis of cell wall of both strains showed presence of about 15 major protein bands whereas Western blot analysis with 21 day soron immunized pig serum showed 16, 33, 47, 63 and 83 kDa polypeptides in both strains. The duration of immune responses were monitored at 3, 6 and 9 months post immunization in pigs. By direct challenge, pigs showed that the vaccines were protective at 21 days and up to 270th day post immunization. Vaccines induced a serum ELISA IgG response that peaked on 60 DPI which declined gradually up to 270th DPI in both vaccines. Stimulation index measured by lymphocyte proliferation test (LTT) indicated that the vaccine, induced cell-mediated immune response and in general percent stimulation index (SI) was higher in pigs immunized with soron vaccine at 15 days post challenge infection. The results showed that pig strain (soron) would be a potential homologous strain of P. multocida for the vaccine against pasteurellosis in place of use of cattle P. multocida P-52 strain.