EVALUATION OF ANTEMORTEM POLYMERASE-CHAIN-REACTION AND SEROLOGIC METHODS FOR DETECTION OF LAWSONIA INTRACELLULARIS-EXPOSED PIGS

Objective-To evaluate polymerase chain reaction (PCR) for detection of Lawsonia intracellularis DNA in feces and an indirect fluorescent ant ibody test (IFAT) for detecting serum IgG antibodies in pigs exposed t o L intracellularis. Animals-15 seven-week-old pigs and 42 three-week- old pigs. Procedure-During 3 experiments, 23 pigs were inoculated with a pure culture of L intracellularis, 31 pigs served as noninoculated controls, and 3 pigs were used as sentinels. Fecal shedding of L intra cellularis was monitored by use of PCR analysis at 7-day intervals. At euthanasia, the ileum was obtained for PCR and histologic analyses. S erum was obtained at 7-day intervals for use in the IFAT. Results-Poly merase chain reaction analysis detected L intracellularis DNA in the f eces of 39% of the inoculated pigs; by postinoculation days 21 to 28, 90% of inoculated pigs developed IgG antibodies detected by IFAT. Neit her L intracellularis DNA nor IgG antibodies were detected in any of t he noninoculated control pigs at euthanasia. Sera from pigs inoculated with enteric pathogens other than L intracellularis did not contain d etectable antibodies that reacted with L intracellularis by use of the IFAT. Conclusion-The IFAT for L intracellularis IgG antibody detectio n appeared to be a more sensitive antemortem test for detecting pigs e xperimentally infected with L intracellularis than was a PCR method fo r direct detection of the organism in the feces. Clinical Relevance-No t all animals that are infected with L intracellularis shed the organi sm in feces at detectable amounts.