3.5 Does Lawsonia intracellularis influence the gut flora (or vice versa)?

Intestinal flora may modify the ability of L. intracellularis to cause proliferative lesions. Germ-free pigs were not susceptible to infection by cell-culture purified L. intracellularis (McOrist et al. 1994). However, pigs exposed to normal intestinal material from L. intracellularis-infected animals developed the disease (McOrist and Lawson 1989). In another study, gnotobiotic pigs inoculated with cultured, normal intestinal flora bacteria along with cell cultured L. intracellularis developed typical lesions of proliferative enteropathy (McOrist et al. 1994).

Dual infections with L. intracellularis and other pathogens in conventional pigs have been described. One or other pathogen may modify the immune response and thus predispose the animal to a dual infection. It has been suggested that diet influences infection in hamsters (Jacoby and Johnson 1981). Pigs, however, on widely dif­ferent diets can be infected (McOrist et al. 1993).