The pathology induced in laboratory rats by metacestodes ofTaenia crassicepsandMesocestoides corti(Cestoda)

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Abstract
Sprague-Dawley rats were infected by i.p. injection with either the cysticerci of T. crassiceps or the tetrathyridia of M. corti. Both species of metacestodes reproduce asexually in the peritoneal cavity. The effect of T. crassiceps upon the rats was to cause chronic inflammation of the peritoneum, fibrous adhesions between the visceral organs and hyperplasia of the gut mesenteries which became extended into a large sac-like structure. Dead parasites surrounded by white calcareous material were found free in the peritoneum and attached to the inner body wall and viscera. The histopathology of the hyperplastic mesenteries and fibrous membrane is described. The tetrathyridia of M. corti were found free in the peritoneal cavity as well as in the liver (mainly the left liver-lobe), gut mesenteries and in an outgrowth of the connective tissue associated with the pancreas. The connective tissue outgrowth comprised 2 layers; an inner reticular layer and a thickened marginal layer. Metacestodes were found in collagen-fibrin capsules within the connective tissue. A layer of mucopolysaccharide material was interposed between the parasite and the capsule wall. A possible method by which the parasites gain entry into the connective tissue is described. The connective tissues of rats harboring either M. corti or T. crassiceps had increased numbers of mast cells compared to connective tissues from control rats. Younger mast cells containing biogenic amines predominated in infected tissues whereas older heparin-containing cells dominated control tissues.