Electron microscopic tracing of pathogenetic events in intestinal chlamydial infections of newborn calves

Pathogenetic events of the penetration of the intestinal mucosa were studied ultrastructurally after oral inoculation of neonatal calves with chlamydial strain LW-613. Chlamydiae adsorbed to the brush border of intestinal epithelial cells and were taken up by endocytosis. Chlamydial replication occurred in the supra-nuclear region of these cells which subsequently degenerated and liberated chlamydiae into the gut lumen and into the lamina propria mucosae. Inter-cellular edema, breakdown of the basal border of the intestinal epithelial cells, and festooning and ultimate loss of the basal lamina facilitated penetration of chlamydiae into the lamina propria mucosae and its cellular components, including the endothelial cells of the lymphatic system. Infected endothelial cells liberated chlamydiae into the lymphatic circulation leading to chlamydemia and systemic infection involving lymph nodes, parenchymal organs and joints.