A series of experiments was conducted to document tumor necrosis factor-alpha (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 microgram/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 microgram/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 chi4232 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 chi4232 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.

Two indirect ELISA containing outer membrane protein (OMP) and lipopolysaccharide (LPS) antigens from a field isolate of Salmonella choleraesuis var kunzendorf were developed and evaluated in experimentally infected and uninfected control pigs. Experimentally induced infection with S choleraesuis was successfully established in 10 pigs by oral inoculation with 10(8) organisms, and 3 pigs died of clinical salmonellosis at postinoculation (PI) weeks 1, 2, and 4. Swab specimens from tonsils, nostrils, and rectum of pigs were obtained for culture, and sera were evaluated at weekly intervals for 9 weeks after inoculation. The ELISA containing OMP and LPS antigens with either anti-swine IgG or protein albumin-to-globulin ratio (antiglobulin) conjugates were standardized for serologic evaluation. All 4 ELISA (2 OMP and 2 LPS) detected seroconversion by PI week 3 and had sensitivities and specificities of 97.8 and 88.8, 100 and 100, 95.6 and 88.8, and 93.3 and 72.5%, at their ideal cutoff points (negative mean optical density + 2 SD). There was excellent agreement between all 4 ELISA systems as determined by kappa values. Cultures of fecal, tonsil, and nasal swab specimens were positive for S choleraesuis until the fourth week of infection. Fecal swab specimens from 1 pig were positive for S choleraesuis until PI week 7. Persistent infection after antemortem culture results were negative was detected by all 4 ELISA, which indicated consistently high titers until the end of PI week 9. Conventional bacteriologic examination of intestines, mesenteric lymph nodes, bone marrow, lung, liver, spleen, and bile yielded positive results for S choleraesuis in the 3 pigs that died of clinical infection, whereas results were negative in the other 7 pigs infected by the end of PI week 9. Histologic examination of lung, liver, spleen, intestines, and mesenteric lymph nodes from the 3 pigs that died of S choleraesuis infection revealed severe ulceration and inflammatory cell infiltration.