SEROLOGIC STUDIES OF EXPERIMENTALLY-INDUCED SALMONELLA-CHOLERAESUIS VAR KUNZENDORF INFECTION IN PIGS

Two indirect ELISA containing outer membrane protein (OMP) and lipopol ysaccharide (LPS) antigens from a field isolate of Salmonella cholerae suis var kunzendorf were developed and evaluated in experimentally inf ected and uninfected control pigs. Experimentally induced infection wi th S choleraesuis was successfully established in 10 pigs by oral inoc ulation with 10(8) organisms, and 3 pigs died of clinical salmonellosi s at postinoculation (PI) weeks 1, 2, and 4. Swab specimens from tonsi ls, nostrils, and rectum of pigs were obtained for culture, and sera w ere evaluated at weekly intervals for 9 weeks after inoculation. The E LISA containing OMP and LPS antigens with either anti-swine IgG or pro tein albumin-to-globulin ratio (antiglobulin) conjugates were standard ized 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 the ir ideal cutoff points (negative mean optical density + 2 SD). There w as excellent agreement between all 4 ELISA systems as determined by ka ppa values. Cultures of fecal, tonsil, and nasal swab specimens were p ositive for S choleraesuis until the fourth week of infection. Fecal s wab specimens from 1 pig were positive for S choleraesuis until PI wee k 7. Persistent infection after antemortem culture results were negati ve was detected by all 4 ELISA, which indicated consistently high tite rs until the end of PI week 9. Conventional bacteriologic examination of intestines, mesenteric lymph nodes, bone marrow, lung, liver, splee n, and bile yielded positive results for S choleraesuis in the 3 pigs that died of clinical infection whereas results were negative in the o ther 7 pigs infected by the end of PI week 9. Histologic examination o f lung, liver, spleen, intestines, and mesenteric lymph nodes from the 3 pigs that died of S choleraesuis infection revealed severe ulcerati on and inflammatory cell infiltration in the lamina propria and submuc osa of the intestine, whereas minimal changes were observed in other o rgans.