Ultrastructural studies of paratuberculosis (Johne's disease) in goats.

Biopsy material of the ileum and corresponding mesenteric lymph nodes from 10 naturally infected goats was studied. In ileum a loss of epithelial cells and infiltration of epitheloid cells, macrophages and a low number of lymphocytes, plasma cells and occasional eosinophils were seen. Ultrastructurally, the epithelial cells showed degenerative changes. Epitheloid cells were characterized by a large nucleus and a wide cytoplasm rich in free ribosomes. Macrophages had been fixed in the process of engulfing bacteria or contained bacteria in phagosomes and phagolysosomes. Large phagolysosomes were common. In macrophages with many or large phagolysosomes, few or no lysosomes were observed. Degenerative changes were seen in macrophages containing many bacteria. Degenerative changes of capillary endothelium were observed. The intercellular spaces were distended by oedema and contained cell debris. The mesenteric lymph nodes were infiltrated with epitheloid cells and macrophages. The ultrastructural picture of these cells was almost identical to that of the ileum. The differences between the changes found in naturally infected and experimentally infected animals are discussed. It is concluded that the mode of infection, the number of bacteria to which the animal is exposed and the intervals between events of exposure may play a role.