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.

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.

Thirty-five heifers were allotted to 3 groups. Group 1 (contro]) consisted of 10 heifers that were not vaccinated and were challenge exposed by breeding to infected bulls. Group 7 (natural challenge exposure) consisted of 10 heifers that were vaccinated and challenge exposed by breeding to infected bulls. Group 3 (experimental challenge exposure) consisted of 15 heifers that were vaccinated and challenge exposed by breeding to infected bulls and by intravaginal inoculation with 10(7) Tritrichomonas foetus. Total immunoglobulin concentrations and specific trichomonal antibodies were determined in serum and vaginal secretions of heifers, using radial immunodiffusion and ELISA procedures. Control heifers remained infected for a mean of 10.6 weeks (range, 0 to 18 weeks), and heifers of the natural and experimental challenge-exposure groups remained infected for 3.2 and 5.0 weeks, respectively (range, 0 to 12 weeks). Total serum and cervicovaginal mucus concentrations of IgM, IgA, IgG1, and IgG2 did not change significantly after vaccination or challenge exposure. However, ELISA titers of total trichomonal antibodies increased up to 1:10,000 (range, 1:400 to 1:10,000) in serum after vaccination, and increased approximately tenfold above background in cervicovaginal mucus. In serum, the predominant trichomonal antibody isotype was IgG1, although trichomonal IgA and IgM antibodies also increased. The predominant trichomonal antibody detected in cervicovaginal mucus was IgA. Antibody titers in serum and cervicovaginal mucus of vaccinated heifers were not increased by infection. However, in control heifers, the total local trichomonal antibody response increased three- to fivefold after infection. In these heifers, specific antibodies in serum were predominantly IgG1 and local (cervicovaginal) antibodies were predominantly IgA.

A rifampicin-resistant Pasteurella haemolytica serotype 1 with 2 added plasmids was used as a colonization-challenge strain in calves to test the resistance to colonization elicited by vaccination. Nine calves were vaccinated with a tissue culture-derived P haemolytica serotype-1 vaccine which, in a prior study, had elicited a serotype-specific inhibition of nasal and tonsillar colonization by the homologous serotype under field conditions. The vaccinates and 9 nonvaccinated control calves were exposed by tonsillar instillation with the challenge strain. The P haemolytica were enumerated in nasal secretion and tonsil wash specimens collected biweekly for 3 weeks. Rifampicin-supplemented agar medium inhibited growth of other bacterial species in the specimens and, thus, increased the sensitivity of detection of the challenge P haemolytica by 100-fold. The challenge strain retained its plasmids during the period of colonization. Inhibition of colonization was evidenced by lower frequency of isolations and fewer isolations of the challenge strain from nasal secretion and tonsil wash specimens of the vaccinates than from those of the nonvaccinates.

A field trial was conducted on a commercial swine farm quarantined because of infection with pseudorabies virus. The purpose was to investigate, in growing pigs born to hyperimmunized sows, the immunogenicity of a vaccine with a glycoprotein I (gE) deletion. One hundred twenty pigs were assigned at random to 1 of 3 vaccination schedules at ages: 8 and 12 weeks; 8, 12, and 14 weeks; and 8, 12, and 16 weeks. Immune response was measured at 8, 12, 14, 16, and 18 weeks, using the serum neutralization test, a screening ELISA, and assays of IgG and IgA in serum and nasal secretions. Results of the serum neutralization test and the screening ELISA indicated that, for pigs vaccinated only at 8 and 12 weeks, the percentage of pigs with pseudorabies virus serum antibodies decreased substantially by 18 weeks; for pigs given a booster at 14 or 16 weeks, the prevalence of serum antibodies at 18 weeks was higher, with 16-week booster vaccination eliciting the best response. At each age, nasal IgA and IgG values were highly correlated (r greater than or equal to 0.70), as were serum IgA and IgG values; correlations of serum with nasal IgA and IgG values were somewhat lower (approx range, r = 0.40 to 0.70). Nevertheless, an increase in serum IgA or IgG values on vaccination was no guarantee of an increase in nasal IgA or IgG values. For serum and nasal mucosal antibodies, a poor immune response was associated with high quantities of maternally derived antibodies. Vaccination at 16 weeks was necessary to ensure eliciting of an immune response in almost all pigs.

Whereas the clinical efficacy of vaccination against pseudorabies has been studied extensively, methods to evaluate the influence of vaccination on pseudorabies virus (PRV) transmission have only recently become available. In this study, PRV transmission and growth performance in finishing pigs vaccinated either once or twice were compared. The incidence of PRV infections was significantly (P = 0.039) higher in the group vaccinated once (38%) than in the group vaccinated twice (10%). The reproduction ratio R, which is defined as the average number of new infections caused by 1 infectious individual, was estimated in both groups. This ratio was also significantly (P = 0.025) higher among single vaccinated pigs (R = 3.4) than among pigs that had received double vaccination (R = 1.5). In compartments where serologic evidence of PRV introduction was observed, the mean daily weight gain was significantly (P = 0.029) lower in pigs vaccinated once (698 g/d) than in pigs vaccinated twice (721 g/d). Results of this study document the possibility to objectively evaluate the effect of vaccination on PRV transmission under field conditions. From the results, we concluded that double vaccination is advantageous in populations of finishing pigs at risk for PRV introduction. However, even among pigs vaccinated twice, extensive spread of PRV can occur.