Immunological studies on a modified water-in-oil-in-water (w/o/w) haemmorhagic septicemia vaccine incorporated with Pasteurella multocida A: 1 in the external aqueous phase.

摘要

Healthy adult New Zealand White rabbits (n=32) of either sex, 1.5 kg, were divided into two groups of 16 animals. Each animal in group I was immunized once with 2 ml bivalent vaccine through deep intramuscular route. The animals of group II received a single intramuscular injection of monovalent P₅₂ vaccine. Eight rabbits were kept as unimmunized controls in each group. Eight rabbits from each vaccinated group were further divided into two groups containing four rabbits in each group. On twenty first DPV, rabbits in group I were challenged with 100 LD₅₀ Pasteurella multocida P₅₂, whereas a second group was challenged with 100 LD₅₀ A:1. Rabbits immunized with bivalent P₅₂ (B:2) vaccine containing alum precipitated A:1 in the external phase showed an early increase in ELISA antibody titres against A:1. Antibody titres against antigen in the internal phase P₅₂ showed a slow increase which peaked around thirtieth DPV and persisted to a significant level up to ninetieth DPV. However, monovalent P₅₂ vaccine showed a classical immune response in which the ELISA antibody titres against P₅₂ peaked around thirtieth DPV and persisted up to ninetieth DPV. Direct challenge infection of rabbits immunized with bivalent vaccine showed 100% protection against both serotypes on twenty-first DPV. On ninetieth DPV, though 100% of the rabbits were protected against P₅₂ challenge, only 50% protection was observed against A:1 challenge. Monovalent P₅₂ vaccine, however, not only showed 100% protection against P₅₂ challenge, but a partial cross protection (25%) was observed against A:1 on twenty-first DPV. The protective immune response against antigen in external aqueous phase is quicker than that of antigen in internal phase. The bivalent vaccine was better than the challenge and PMPT were higher in the bivalent group.