Ultrastructure of the small intestine in astrovirus-infected lambs.

The ultrastructure of the small intestine of gnotobiotic lambs infected with lamb astrovirus was studied. The virus was observed from 14 to 28 h p.i. in mature columnar epithelial cells covering the apical two-thirds of villi. Crystalline arrays of virus particles with a centre to centre distance of approx. 29 nm were seen in the cytoplasm and virus particles were also observed in apical pits and tubules and in lysosomes. Macrophages containing virus particles in lysosome-like organelles were seen in the lamina propria. Virus particles were released by desquamated cells disintegrating in the gut lumen. Cuboidal cells lining villi appeared from 38 to 70 h p.i., and by 120 h p.i. the villi appeared normal.