Histopathological effects of the intramolluscan stages of Zygocotyle lunata, Echinostoma trivolvis, and Ribeiroia ondatrae on Helisoma trivolvis and observations on keratin in the trematode larvae.

The histopathological effects of Zygocotyle lunata, Echinostoma trivolvis, and Ribeiroia ondatrae in naturally infected Helisoma trivolvis were studied in hematoxylin and eosin sections of infected digestive glands fixed in 10% neutral buffered formalin. The larval stages of all three trematodes damaged the snail digestive gland. Most notable histopathology included disrupted digestive gland tubules, lysed cells, compressed tubules, and edematous spaces between tubules. Considerable damage was done by rediae ingesting digestive cells. There was a detectable hemocytic response by H. trivolvis in response to the rediae and cercariae of Z. lunata. Histochemical studies on sectioned material stained with the Ayoub-Shklar method for keratin detected the presence of this protein in the rediae and cercariae of Z. lunata and R. ondatrae. The presence of keratin is probably related to its role in cercarial encystment.