Intranasal vaccination of rabbits with Pasteurella multocida A : 3 outer membranes that express iron-regulated proteins

Objective-To determine efficacy of intranasal vaccination of rabbits with P asteurella multocida A:3 outer membrane proteins (OMP) expressing iron-regu lated OMP (IROMP) in conferring protection against experimental challenge e xposure. Animals-52 male New Zealand White rabbits. Procedure-Rabbits were vaccinated intranasally on days 0, 7, and 14; some v accines included cholera toxin (CT) as an adjuvant. Concentrations of intra nasal IgA and serum IgG antibodies against P multocida OMP were determined. In experiment A, rabbits were vaccinated with either phospate-buffered sal ine solution (PBSS), PBSS-CT, OMP-CT, or IROMP-CT, challenge-exposed intran asally on day 16, and euthanatized and necropsied on day 28. Rabbits were a lso vaccinated with OMP or IROMP without CT and were not challenge-exposed. In experiment B, rabbits were vaccinated with PBSS, PBSS-CT, IROMP, or IRO MP-CT. On day 17, rabbits were challenge-exposed intranasally. Nasal bacter ia and antibodies were determined on day 24. Results-In experiment A, OM P-CT vaccination stimulated mucosal and systemi c antibody responses to the bacterium and enhanced resistance against chall enge exposure. Intranasal bacterial counts were not significantly reduced. Vaccination with IROMP-CT stimulated mucosal and systemic antibodies, enhan ced resistance to challenge exposure, and significantly reduced nasal bacte rial counts. In experiment B, natural infection was detected in several rab bits at challenge exposure; however, IROMP-CT-vaccinated rabbits had signif icantly higher serum and nasal antibody responses, compared with other rabb itsIROMP-CT-vaccinated rabbits had significantly lower nasal bacterial coun ts compared to control rabbits. Conclusions and Clinical Relevance-Intranasal vaccination of rabbits with P multocida outer membranes containing IROMP and CT stimulated immunity agai nst experimental pneumonic pasteurellosis.