Adult cestodes

The adult cestode special structural features relevant to its physiology... 

Fig. 2.1. Diagrammatic representation of the tegument of a typical adult cestode, based on several species. (After Threadgold, 1984.)...

Table 2.2. Species of adult cestodes with scolex glands, investigated by Kuperman Davydov (19826).

Pig. 2.6. Three types of secretory mechanisms found in the scolex glands of adult cestodes. (After Kuperman Davydov, 19826.)... 

Cestodes produce a range of end-products as a result of their respiratory metabolism (Table 5.4). Bryant Flockhart (104) have usefully divided the patterns of respiratory metabolism among parasitic helminths into three types. The metabolism of larval and adult cestodes fits broadly into the first two categories of this biochemical classification and these are illustrated in Fig. 5.4. Type 1 contains the homolactate fermenters in which carbohydrate is degraded, via glycolysis, to lactate and excreted. The ANU (Australian) strain of H. diminuta tends towards this type of metabolism (see below). 

Table 8.1. Fine structure of glands in larval pseudophyllidean cestodes species investigated by Kuperman Davydov f1982a). For glands in adult cestodes, see Table 2.2...

Since adult cestodes, freshly removed from a host gut, are invariably covered with a mucus film containing micro-organisms such as yeasts, bacteria and fungi, most workers have used larval stages, which invariably occur in sterile habitats, as initial culture material. Nevertheless, by application of antiobiotics certain species of adult cestodes (e.g. H. diminuta, E. granulosus) may readily be cultured in vitro after removal from the definitive host before the end of the pre-patent period and then maintained in vitro, when egg release is safely contained within the culture vessel (736,811, 867). 

For many years, it was generally held that adult cestodes were non-immunogenic or poorly immunogenic (353). This view appeared to be based on the assumption that the scolex of most cestode species made only a loose, non-penetrative contact with the intestinal mucosa. It was recognised that an exceptional case was that of H. nana, which has a larval tissue phase in the villi of man and mice (Fig. 11.6) (which is strongly immunogenic) as well as an adult stage. 

The concept that the scolex of adult cestodes is generally non-penetrative has been shown not to hold for species such as Echinococcus granulosus and E. multilocularis, where the scolex penetrates the crypts of Lieberkiihn and, occasionally, even the lamina propria (Fig. 9.5) often resulting in a complete breakdown of the mucosal epithelium. These species can be regarded as both tissue and lumenal parasites. That the scolex contact is close is reflected in the fact that anti-Echinococcus antibodies appear in dog sera 14 days post-infection (p.i.) (368). It is likely, however, that in many cestodes the scolex contact is more superficial and breakdown of the mucosa may not occur, especially in those species which undergo diurnal migration - see Chapter 9. 

Before discussing the immunological reactions to adult cestodes, it is important to review our present knowledge of the immunobiology of the vertebrate intestine, about which many new data have become available in recent years (53,55,80,81). The account below summarises briefly the local aspects of mucosal tissue responses (Fig. 11.2) which appear to be important in parasitic infections. An important concept which has emerged from these recent data is that local immunoregulatory events in mucosal infections may be distinct from those seen in systematic sites (55). 

Most research on immunity to adult cestodes has been carried out on the Hymenolepididae in laboratory animals, with comparatively few studies... 

Andreassen, J. (1981). Immunity to adult cestodes. Parasitology (EMOP Proceedings, 4) 82 153-9. 

The fine structure of frontal glands in adult cestodes. International Journal for Parasitology, 12 285-93. 

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