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 antibody test (IFAT) for detecting serum IgG antibodies in pigs exposed to 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 intracellularis was monitored by use of PCR analysis at 7-day intervals. At euthanasia, the ileum was obtained for PCR and histologic analyses. Serum was obtained at 7-day intervals for use in the IFAT.
Results: Polymerase chain reaction analysis detected L intracellularis DNA in the feces of 39% of the inoculated pigs; by postinoculation days 21 to 28, 90% of inoculated pigs developed IgG antibodies detected by IFAT. Neither L intracellularis DNA nor IgG antibodies were detected in any of the noninoculated control pigs at euthanasia. Sera from pigs inoculated with enteric pathogens other than L intracellularis did not contain detectable antibodies that reacted with L intracellularis by use of the IFAT.
Conclusion: The IFAT for L intracellularis IgG antibody detection appeared to be a more sensitive antemortem test for detecting pigs experimentally infected with L intracellularis than was a PCR method for direct detection of the organism in the feces.
Clinical Relevance: Not all animals that are infected with L intracellularis shed the organism in feces at detectable amounts.