Ultrastructural characterization of colonic lesions in pigs inoculated with Treponema hyodysenteriae.

Twelve pigs were inoculated orally with pure cultures of Treponema hyodysenteriae. Pigs were necropsied at different time intervals postinoculation; colonic specimens were collected and prepared for light and electron microscopy. The earliest colonic lesion detected by electron microscopy consisted of superficial vascular congestion and dilatation, edema of the lamina propria and intercellular separation of the epithelial cells at the crypt shoulders. This lesion progressed to epithelial cell necrosis and extrusion into the lumen and extravasation of red cells. Large numbers of spirochetes were present and free, between, over and under necrotic epithelial cells whether in place or partially extruded. Spirochetal penetration of colonic enterocytes and intracytoplasmic multiplication were confirmed in this study. The spirochetes were found to invade the epithelial cells only from their lateral borders. The relationship between T. hyodysenteriae and the colonic anaerobes was not determined.