Pathology of infection with Paramphistomum ichikawai in sheep.

Lambs were given 40,000 or 50,000 metacercariae of Paramphistomum ichikawai by injection into the rumen and necropsied at 21, 42 and 84 days after infection. Pathological changes were observed grossly and confirmed histologically in the small intestine and rumen. The numbers of flukes and their location in the gastrointestinal tract were recorded and the populations of eosinophils, mast cells and globule leucocytes estimated. Changes varied, according to the numbers of flukes present, from a localised enteritis and villous atrophy in the duodenum in light infections to severe destruction of the mucosa extending into most of the jejunum in heavy infections. As the infection progressed changes were characterised by extensive thickening and fibroplasia in the mucosa and submucosa. Severe damage to the mucosa of the rumen was also observed in heavy infections. Heavy infections were associated with increased infiltration with eosinophils. Mast cells were generally depleted and globule leucocytes only appeared after the flukes had left the small intestine. Migration of the flukes from the small intestine was delayed in heavy infections exacerbating the effect of the infection. It is suggested that the presence of 20,000 to 25,000 flukes would result in clinical disease; smaller numbers would cause significant subclinical disease.