Paratuberculosis is an economically highly important disease of cattle and small ruminants caused by Mycobacterium avium ssp. paratuberculosis. Host-pathogen interactions during the long clinically inapparent incubation period prior to the onset of disease are not well known, but are a major determinant to the outcome of disease. An experimental model of infection has been established in goats (collaboration with Dr. H. Köhler, Workgroup Mycobacteria). Using this model, lesions, distribution of MAP and cellular reactions at the sites of lesions are investigated during the clinically inapparent incubation period.