Ultrastructural changes in the small intestinal epithelium of suckling pigs affected with a transmissible gastroenteritis (TGE)-like disease.

The small intestine of piglets collected during a sudden outbreak of diarrhoeal disease resembling transmissible gastroenteritis (TGE) was examined by light and electron microscopy. The principal histopathological changes were moderate infiltration by mononuclear cells in the lamina propria of the villi and cytoplasmic vacuolation. These were most pronounced in the epithelial cells covering the villous tips. By scanning electron microscopy, the intestinal villi were swollen and the transverse furrows disappeared. Microvilli were reduced in number leaving denuded areas on the brush border of the villous epithelial cells. The ultrastructural changes were restricted to the cytoplasm of affected villous epithelial cells. The cell organelles were missing in rounded areas leaving cleared areas in the cytoplasm. Parallel fascicles and bundles were seen in these areas. Viral particles with an average diameter of 70 nm were found within the dilated apical tubulo-vesicular system, free in the cytoplasm, among the microvilli, or lying free in the intestinal lumen. Viral particles surrounded a non-membrane bound viroplasm in some cases. The negatively stained particles showed a typical coronavirus morphology. These particles were found to be distinct from the known coronaviruses of swine, TGE virus and hemagglutinating encephalomyelitis virus by immune electron microscopy.