SUMMARY
Field cases of infectious stunting syndrome, and experimental cases produced by inoculating one day old chicks with intestinal homogenates obtained from field cases, were studied. Samples for histopathological investigation were taken from the intestine, pancreas, proventriculus, thymus, bursa of Fabricius, spleen, liver and heart at 14, 21, 28 and 35 days of age from field and experimental cases. Intestinal segments were fixed in 5% cacodylate buffered glutaraldehyde for scanning electron microscopy. Marked reduction in the live weight was observed in the affected chickens at 21, 28 and 35 days. Similarly, the mean weight of the intestine, pancreas, thymus, bursa of Fabricius and spleen of the stunted chickens was severely reduced than the control at all age groups. Degeneration and necrosis of the enterocytes in the crypts of Lieberkuhn and infiltration of the lamina propria of the villi with lymphocytes and macrophages were the prominent intestinal lesions, crypt abscesses were observed from 14 days of age. SEM demonstrated atrophy and fusion of the intestinal villi, desquamation of the microvilli from the brush border of the villous enterocytes and finally loss of the enterocytes from the tips of the villi. Pancreatic lesions were degenerative in young birds and proceeds to atrophy and fibrosis in older ones. Proliferative vasculitis was observed at 14 days of age only in field cases. Focal pancreatitis was evident in field cases at 35 days. Proventriculitis was a constant finding in most cases. There was marked atrophy of the thymus, bursa of Fabricius and spleen. Several reovirus isolates were isolated from gastrointestinal homogenate and visceral organs of the affected chicks and their possible role in the production of the stunting syndrome was discussed. As a result of this study, it is apparent that ISS causes significant intestinal and pancreatic lesions which affects the process of digestion and absorption of food with subsequent
reduction of the growth rate