Infectious stunting syndrome of chickens in Great Britain: intestinal ultrastructural pathology.

The ultrastructural pathology of the intestine of field and experimental cases of 4- to 6-day-old chickens showing early signs of stunting syndrome was studied. Changes were most frequently observed in the lamina propria, with infiltrations of lymphoid cells, mesenchymal cells and macrophages. Cysts were observed in the crypts. Early, small cysts were lined with both epithelial cells and myofibroblasts, with no underlying basement membrane. Larger cysts were composed of cuboidal epithelial cells surrounded by a basement membrane with underlying fibroblasts and collagen fibrils. Membrane-bound cytoplasmic inclusions containing picornavirus-like particles about 20 nm in diameter were present in mesenchymal cells and macrophages in the lamina propria, both at the base of the villi and in the corium of the villus. Cells containing particles were associated with early cysts, but not with large, mature cysts. Particles were occasionally observed in enterocytes, particularly in field cases. A brief description of the normal chick intestinal lamina propria is also included.