Fine Structure of the Hydatid Cyst and Protoscolex of Echinococcus granulosus

Abstract

The fine structure of various parts of the hydatid cysts and the enclosed protoscolex is described. The contents of the brood capsule are PAS-positive following extraction treatment with amylase. This material is made up of fine irregularly arranged filaments, and remains as a coating over the posterior aspect of the protoscolex after its removal from the brood capsule. It has completely disappeared after 42 days in vitro. The posterior aspect of the protoscolex is with knoblike projections which are probably undeveloped tegumental projections. After 42 days culture in vitro this area has fully developed tegumental projections. Multinucleation of tegumental cells is common in the protoscolices cultured for 42 days in vitro. The various organ systems are described and compared with similar structures reported for tapeworms and other invertebrates. Although the teguments of several species of adult tapeworms have been examined by electron microscopy, the fine structure of the intermediate stages in their life history has been neglected. Goldschmidt (1900) was apparently the first to describe the spines on the body surface of developing protoscolices of Echinococcus granulosus, and subsequently Coutelen (1927) described the surface distribution of these spines in more detail. These authors, though limited to light microscopy, stated that the spines were seen only under ideal conditions with an oil immersion objective. More recent workers have made similar observations on the cystic stage of several taeniid tapeworms (Crusz, 1948; Voge, 1962, 1963). Waitz (1961) in describing the ultrastructure of the cystic stage of Hydatigera taeniaeformis mentions the presence of microvilli on the body surface. Larsh et al. (1965) in a study on the histopathology of infections in mice with the cystic stage of Multiceps serialis include an electron micrograph of a portion of cyst wall (their figure 7). Although a discussion of the fine structure is outside the scope of their paper, it is significant that their illustration clearly shows surface projections, vesicles within the tegument, and dark structures which may be mitochondria. Siddiqui (1963) examined the tegument of cysticerci of Taenia saginata, T. hydatigena, and T. pisiformis and noted that all three species were covered with hair-like processes. In an account of the ultrastructure of the Received for publication 27 July 1966. cystic stage of M. serialis, Race et al. (1965), reported that the subcuticular canals connect the cuticle with the parenchyma. Marzullo et al. (1957) reported the presence of mucopolysaccharides in the cyst of E. granulosus. Kilejian et al. (1961) demonstrated that the brood capsule contents are PAS-positive after saliva treatment. The electron microscopic appearance of this material has not previously been demonstrated. The investigation reported in this paper is an extension of previous work on the fine structure of adult taeniid tapeworms (Morseth, 1965, 1966) and especially that of E. granulosus. MATERIALS AND METHODS