Intestinal pathology associated with Trichostrongylus colubriformis infection in sheep: vascular permeability and ultrastructure of the mucosa.

Increased permeability of capillaries and venules, labelled with colloidal carbon, was observed in the superficial mucosa of the small intestine of sheep infected with Trichostrongylus colubriformis. The labelled vessels were restricted to infected portions of the gut, and the intensity of labelling appeared to be related to density of the worm population. Open junctions were seen between endothelial cells in permeable vessels. In moderately atrophic infected intestine, enterocytes were domed, had sparse, short, distorted microvilli and many polyribosomes. Tight junctions between enterocytes seemed to be intact and distended intercellular spaces were seen. In more severely atrophic mucosa, enterocytes had distended mitochondria and endoplasmic reticulum, bizarre shapes, and the continuity of the epithelial sheet was occasionally disrupted. There was oedema in the lamina propria and neutrophils were seen in migration to the lumen of the gut. The possible mechanisms inducing these changes and their significance in terms of plasma protein loss and intestinal function are discussed.