Diagnosis of Lawsonia intracellularis infection in pigs after vaccination or antimicrobial treatment.

Diagnosis of infection with Lawsonia (L.) intracellularis, the causative agent of porcine proliferative enteropathy, is routinely based on the detection of L. intracellularis in faeces and/or tissue samples by PCR. Furthermore, infection can be determined by the detection of antibodies in serum samples. The aim of this comparative study was to examine whether results from molecular biology and serological testing are influenced by applying live bacteria vaccine Enterisol Ileitis or antimicrobial treatment to pigs naturally exposed to L. intracellularis. Decreased shedding was detected in tylosin treated pigs only. Thus, the distribution of 345 pigs into groups of 0-, 1- or > or = 2-times positive by PCR was significantly influenced by the treatment (P < 0.0001). A global effect of positive PCR results on average daily weight gain was also highly significant (P < 0.0001). The serological reaction was detected by a blocking ELISA after infection but not after vaccination independent of treatment. The results indicate no influence of vaccination on applied diagnostic tests.