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Abstract

Objective

To establish the effect of dose on persistence of and immune response to Salmonella choleraesuis in swine.

Design

19 Salmonella-free pigs were allotted to 4 groups. Groups 1 (n = 5), 2 (n = 5), and 3 (n = 5) were inoculated intranasally with 109, 106, and 103 colony-forming units of S choleraesuis, respectively. Group 4 (n = 4) served as uninoculated controls.

Procedure

Pigs were monitored for clinical signs of disease and bacterial shedding. Serum and lymphocytes were obtained to measure immune responses. Pigs from groups 1, 2, and 4 were necropsied at postinoculation (PI) weeks 6 and 15. Pigs from groups 3 and 4 were necropsied at PI weeks 6 and 10.

Results

Pigs in group 1 shed S choleraesuis through PI week 15 and were tissue positive at PI weeks 6 and 15. Pigs in group 2 were tissue positive for S choleraesuis until PI week 6 and continued shedding through PI week 9. Salmonella choleraesuis was not recovered at any time from pigs in groups 3 or 4. Pigs in groups 1, 2, and 3 had serum IgG and IgM titers to S choleraesuis lipopolysaccharide and soluble antigens. Pigs in all groups had a lymphocyte response to concanavalin A, and pigs in groups 1 and 2 had a lymphocyte response to S choleraesuis endotoxin. Pigs in group 1 had a lower stimulation index in response to both antigens, indicating some form of lymphocyte immunosuppression.

Conclusions

Persistence of S choleraesuis in host tissues is dose dependent. Short-term persistence can occur after a dose as low as 106 colony-forming units of S choleraesuis. Higher doses result in development of longterm carrier status, which may be related to the observed lymphocyte immunosuppression.(Am J Vet Res 1996;57:313-319)

Free access
in American Journal of Veterinary Research

SUMMARY

A series of experiments was conducted to document tumor necrosis factor-α (tnf) activity in serum of swine after inoculation with Salmonella spp endotoxin and after oral or respiratory tract challenge exposure with live Salmonella spp. For experiment 1, a potentially lethal dose of S typhimurium endotoxin (25 μg/kg of body weight) was administered iv, and serum tnf activity was measured. High tnf (approx 700 IU/ml) activity at 1 to 2 hours after administration of the inoculum was associated with death, whereas lower tnf (approx 30 IU/ml) activity was associated with a general prolonged state of shock. For experiment 2, pigs were administered a nonlethal dose (5 μg/kg, iv) of either S typhimurium or S choleraesuis endotoxin. Difference in the ability to induce porcine serum tnf activity was not observed between strains. During experiment 3, pigs were inoculated with 104 colony-forming units of S typhimurium χ4232 either orally by gelatin capsule (gc) or by intranasal (in) instillation. A late serum tnf response (17 IU/ml) was measured at 6 weeks after in inoculation. A serum tnf response was not detected in gc-inoculated pigs. All tissues and feces were test-negative for S typhimurium prior to the 6-week tnf response. Serum tnf activity may be related to clearance of S typhimurium after respiratory tract exposure, but it is not important to or indicative of clearance of orally presented S typhimurium in swine. During experiment 4, pigs were inoculated with 106 colony-forming units of S typhimurium χ4232 similarly as for experiment 3. Challenge exposure with this medium-size dose of inoculum induced a prolonged peak serum tnf response (37 IU/ml) between 2 and 4 weeks after in inoculation. Again, serum tnf activity was not detected in gc-inoculated pigs. Data suggest that clearance of a medium-size dose (106) of inoculum may be influenced by the prolonged higher serum tnf activity. For experiments 5 and 6, pigs were inoculated in with 103, 106, 108, or 109 S choleraesuis χ3246. A measurable, yet statistically nonsignificant, serum tnf response was observed for all doses. Pigs inoculated by gc with 108 S choleraesuis χ3246 had similar results. High doses (> 106) of live S choleraesuis were associated with clinical signs of endotoxic shock. Clearance of S choleraesuis, or lack thereof, did not correlate with serum tnf activity.

Free access
in American Journal of Veterinary Research

Objective

To compare prevalence of fecal shedding of Salmonella organisms and serum antibodies to Salmonella sp in market-age pigs housed in barns with partially slotted floors or solid floors with openflush gutters.

Design

Cross-sectional study of prevalence.

Sample Population

Finishing-age pigs deemed by the producer to be within 1 month of slaughter.

Procedure

Fecal and serum samples were obtained from a group of 121 pigs housed in a barn with solid floors (31 fecal samples, 30 serum samples) and from a group of about 400 pigs housed on partially slotted floors (57 fecal samples, 64 serum samples). Fecal samples were submitted for bacteriologic culture to detect Salmonella organisms, and serum samples were tested for antibodies by use of ELISA.

Results

Salmonella agona was isolated from 26 of 31 (84%) fecal samples obtained from pigs housed in the open-flush gutter barn, compared with 5 of 57 (9%) fecal samples from pigs in the barn with slotted floors. Median value for optical density was higher for serum samples from pigs housed in the openflush gutter barn.

Clinical Implications

Housing of finishing-age swine in barns with open-flush gutters may contribute to increased shedding of Salmonella sp. Analysis of our observations indicated that repeated exposure to infected feces is important in prolonging fecal shedding by swine. (J Am Vet Med Assoc 1997;210:386–389

Free access
in Journal of the American Veterinary Medical Association

Objective

To test feed and feed ingredients on swine farms for Salmonella organisms and to analyze data from these farms to determine risk factors associated with Salmonella organisms in the feed and feed ingredients.

Design

Epidemiologic survey and retrospective case-control study.

Sample Population

30 swine farms.

Procedure

Samples of feed and feed ingredients and information regarding herd characteristics were collected from 30 swine farms. Samples were tested for Salmonella organisms, and data compiled from herd information forms were examined for associated risk factors between herd characteristics and isolation of Salmonella organisms.

Results

Salmonella organisms were isolated from 36 of 1,264 (2.8%) feed and feed ingredient samples and from 14 of 30 (46.7%) farms. Thirteen Salmonella sp serotypes and 2 untypeable isolates were cultured. Recovery of Salmonella organisms from at least 1 feed or feed ingredient on a farm was significantly associated with 6 herd characteristics (lack of bird-proofing, using farm-prepared feed for finishing-age pigs rather than purchased feed, and housing pigs in facilities other than total confinement in the growing, finishing, gestating, and breeding stages of production, respectively). Isolation of Salmonella sp was not associated with a history of salmonellosis on a farm.

Clinical Implications

Salmonella organisms were readily isolated from samples of feed and feed ingredients, illustrating that salmonellae are ubiquitous in a farm environment. Implementing sanitary and pestcontrol measures continues to be a prudent recommendation. Salmonella serotypes found in feed and feed ingredients have the potential to cause disease in pigs that consume the feed or, ultimately, in people that consume pork. (J Am Vet Med Assoc 1997;210: 382–385

Free access
in Journal of the American Veterinary Medical Association