DEVELOPMENT OF PERSISTENT INTESTINAL INFECTION AND EXCRETION OF LAWSONIA-INTRACELLULARIS BY PIGLETS

Challenge experiments using Lawsonia intracellularis as oral inocula h ave established its aetiological role in porcine proliferative enterop athy. Thirty piglets, in four groups, were weaned at 21 days of age an d inoculated orally at 24 days. Six piglets were challenged with 1.0 x 10(8) L intracellularis strain 916/91 (NCTC 12657) passaged 12 times in vitro, six with 5.0 x 10(8) of the same strain, seven with 3.0 x 10 (8) L intracellularis strain LR189/5/83, passaged nine times, and 11 c ontrols were dosed with sucrose-potassium glutamate buffer. An immunof luorescence assay for L intracellularis was applied to faecal smears a nd a polymerase chain reaction (PCR) incorporating L intracellularis-s pecific primers was applied to extracts of bacterial DNA derived from the faeces samples. Up to five pigs in each challenge group excreted d etectable L intracellularis in faeces, in samples taken between two an d 10 weeks after challenge. Some of the pigs had up to 7 x 10(8) L int racellularis g(-1) faeces. The average weight gains of the higher dose challenge groups were moderately below those of the control pigs betw een three and nine weeks after challenge; diarrhoea was also observed in six pigs, two to four weeks after challenge. Numerous L intracellul aris were detected in the intestines of all the pigs challenged with s train LR189/5/83 and two of the pigs challenged with 916/91, but not i n other tissues.