Echinococcus granulosus: studies on the development of the metacestode tegument.

Abstract

Protoscoleces of the horse strain of Echinococcus granulosus were successfully cultured both in vitro and in BALB/c mice to produce small hydatid cysts. In vitro cysts were formed from vesiculating protoscoleces and also from posterior bladders and portions of brood capsule wall which had detached from the protoscoleces. In vivo cysts were produced after intraperitoneal Injection of protoscoleces and after their Implantation within diffusion chambers. The latter method proved to give a higher yield of cysts although these were generally small In size. Prior to, and during cystic differentiation the ultrastructure of the tegument was monitored using scanning and transmission electron microscopy. Initially the protoscolex tegument showed regional variations in vesicle population and surface projections. Three main types of vesicle were identified, at least two of which were thought to be of Golgi origin. During differentiation considerable change occurred in the tegument and two further vesicle types were observed. The possible function of these and other organelles is discussed with reference to parasite survival and the formation of the carbohydrate-rich laminated layer around the cyst. Production of subsequent protoscoleces within cysts, in vivo. Involved several developmental stages. Of particular Interest were the changes in the surface projections. Involving the transitory appearance of microvilli and enlarged microtriches, some of which were involved in rostellar hook formation. Throughout metacestode development and maturation the Importance of the Golgi complex was evident. In an attempt to disrupt this system, and hence parasite development, the effects of the lonophore monensin were monitored in cysts and protoscoleces. In vitro all parasites were killed by the action of monensin. Attempts to reproduce these events In vivo were much less successful although certain effects were observed. It was concluded that, due to probable difficulties with drug absorption and host toxicity, monensin was an unlikely chemotherapeutic agent for hydatidosis.