An avirulent live Salmonella choleraesuis culture (SC-54) was evaluated for use as an effective vaccine in preventing salmonellosis caused by S choleraesuis in pigs. Eighty-two pigs, 3 to 4 weeks old, were randomly assigned to 1 of 2 treatment groups, which were designated as either vaccinates or controls. After vaccination, all pigs were examined for fecal shedding of S choleraesuis, rectal temperature, and 10 clinical variables. Significant difference was not detected between vaccinated and nonvaccinated pigs for 14 days (phase I) after intranasal administration of the vaccine. Efficacy and duration of immunity were examined by intranasally challenge exposing respective pigs from either treatment group with a virulent field isolate of S choleraesuis at 2, 8, or 20 weeks after vaccination (phases II-IV). Pigs were again evaluated for 14 days after challenge exposure, and 10 clinical variables and rectal temperature were monitored. Surviving pigs were euthanatized and evaluated for gross lesions, and samples of 7 organs were collected. These organ samples were homogenized, and level of S choleraesuis infection was determined. After virulent challenge exposure during phases II-IV, the clinical status of the SC-54 vaccinates was significantly (P < 0.05) superior to that of nonvaccinates for rectal temperature, feces consistency, behavior, appetite, body condition, and mean score for the 10 clinical variables. Quantitative bacteriologic culture of the tonsil, lung, liver, spleen, mesenteric lymph nodes, ileum, and colon samples indicated consistent reduction of organ colonization in vaccinates; bacteria numbers in the mesenteric lymph nodes, lungs, and ileum were significantly (P < 0.05) reduced. Gross lesions in pigs indicated reduction of pneumonia in vaccinates. Pigs also had consistent weight gain throughout all phases of the study after challenge exposure, although the differences were not significant. In conclusion, a single intranasally administered dose of SC-54 given to 3- to 4-week-old pigs proved to be safe and efficacious and to provide protection to pigs at least 20 weeks after initial vaccination.

Four colostrum-deprived calves each were immunized passively with antisera to whole Pasteurella haemolytica, leukotoxin-containing supernatants of P haemolytica, P haemolytica lipopolysaccharide, or newborn calf serum. Calves were challenge exposed intrabronchially with 5 X 10(9) P haemolytica, and 24 hours later, the resulting lesions were evaluated. The greatest protection against challenge exposure was provided by the antiserum to whole P haemolytica (lesion score = 6.3), whereas newborn calf serum provided the least protection (lesion score = 28.3). Calves that received antiserum to P haemolytica supernatants were moderately protected (lesion score = 16.3), and the antiserum to lipopolysaccharide provided minimal protection (lesion score = 21.8). Antibodies that were unique to whole P haemolytica antiserum and produced dense bands on immunoblots were detected to antigens at 66, 50, and 30 kd. Antibodies in the supernatant preparation that produced prominent bands reacted to antigens between 100 and 90 kd. Collectively, antibodies to these antigens may be responsible for enhancing resistance to experimentally induced pneumonic pasteurellosis. Antibodies to antigens in P haemolytica lipopolysaccharide provided little to no protection.

Administration of an N-lauroylsarcosine-derived outer membrane protein fraction of Pasteurella haemolytica A1 (SCI-1) induced a protective response in calves against intrathoracic challenge exposure with the homologous serovar. Outer membrane proteins from heterologous serovars, A6 and A9, induced partial protection that was associated with their respective similarities to serovar A1 in outer membrane protein profiles derived by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Calves vaccinated with SCI preparations did not have detectable neutralizing antibody to P haemolytica A1 leukotoxin. Antibodies to whole-cell antigens, carbohydrate-protein subunit antigen, and SCI-1 were associated with resistance, which indicates that protein antigens shared among cell surface, carbohydrate-protein subunit, and SCI preparations are immunogenic and enhance resistance to experimental challenge exposure.