Rabbit pasteurellosis: induced disease and vaccination

Pasteurellosis was induced in rabbits by conjunctival inoculation with 2 strains of Pasteurella multocida. The LD50 of strain P1062 (a bovine isolate) was 10(5.1) colony-forming units and that of strain P1059 (a turkey isolate) was 10(5.5) colony-forming units. Pasteurella-free rabbits were vaccinated IV or mucosally with boiled cells of P multocida or a cross-reactive uridine diphosphogalactose epimerase-deficient mutant of Escherichia coli J5. In rabbits challenge exposed with P multocida strain 1062 or 1059, homologous P multocida strain gave the best protection against fatal bacteremia. Partial protection was provided by J5; mucosal routes of vaccination (aerosol or conjunctival) gave better protection than did the IV route. Serum antibody titers were lower in rabbits vaccinated by mucosal routes than in those vaccinated IV. Cross-reactive IgG and IgM titers to P multocida were demonstrated when rabbits were vaccinated with J5. On the basis of bacteriologic examination of nasal secretions, rabbits that died were considered culture positive sooner than were those that survived. On the basis of bacteriologic examination of blood, rabbits that died were considered culture positive, and those that survived were considered culture negative. Seemingly, heat-stable antigens were protective, the cross-reactive E coli J5 mutant (with only core lipopolysaccharide) provided partial protection against pasteurellosis, and the mucosal route was somewhat useful for cross-protective immunization.