The scolex

Cestodes live in what might be termed a hazardous environment, in which the peristaltic movement of the gut and the passage of partly digested food make the possession of an efficient form of attachment an essential prerequisite for survival. 

The various forms of cestode scolex or holdfast are well known and are described in standard texts (32, 345,800,933). In general, the morphology 

The bothriate type of scolex consists typically of a pair of shallow, 

Glands in the rostellar region of the scolex of a number of Cyclo-phyllidea, e.g. Hymenolepis spp., Taenia solium, T. crassiceps, Davainea 

Eubothrium rugosum E. salvelini E. crassum E. acipenserinum Bothriocephalus gowkongensisP B. scorpii B. claviceps 

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Quinacrine concentrates in the scolex of the parasite and causes the muscles needed for holding onto the intestinal wall to relax. The worms are stained yellow and pass from the body, still aUve. Quinacrine can intercalate with DNA and inhibit nucleic acid synthesis. It creates fluorescent bands in deoxyadenylate—deoxythmidylate-rich regions of DNA and has been used as a stain in the study of human genetics. 

Niclosamide inhibits oxidative phosphorylation and stimulates adenosine tripho-sphatese activity in the mitochondria of cestodes, killing the scolex and proximal segments of the tapeworm both in vitro and in vivo. The scolex of the tapeworm, then loosened from the gut wall, may be digested in the intestine and thus may not be identified in the stool even after extensive purging [90,91], Niclosamide is not appreciably absorbed from the gastrointestinal tract [92,93] and the side effects have primarily been limited to gastrointestinal symptoms. 

The drug affects the scolex and proximal segments of the cestodes, resulting in detachment of the scolex from the intestinal wall and eventual evacuation of the cestodes from the intestine by the normal peristaltic action of the host s bowel. Because niclosamide is not absorbed from the intestinal tract, high concentrations can be achieved in the intestinal lumen. The drug is not ovicidal. 

The majority of adult tapeworms have an attachment region, the scolex, from which a series of proglottids develop, giving the animal a segmented appearance proglottids distal to... 

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

In cestodes, most, perhaps all, of the neural elements are found in the ganglia of the scolex and the main nerve tracts. In these, the cell bodies are arranged peripherally around a core made up of a tangled mass of neuronal processes often referred to as neurites because it is impossible to distinguish between axons and dendrites. This mass constitutes the so-called neuropile . Like all differentiated cells in cestodes - and probably in all invertebrates - nerve cells are incapable of mitosis and hence new nerve cells must arise directly from the germinative ( = stem) cells (276). In D. dendriticum, the neuropile is composed of a dense network of unmyelinated nerve fibres with no extracellular stroma between the fibres (277). The fibres differ mainly in the content of different types of vesicles, which can be dense-core, small clear or large clear vesicles. The structure of synapses is discussed further on pp. 25—7. 

In the scolex ganglion of the tetraphyllid Pelichnobothrium speciosum, where unipolar and multipolar neurones are found, the nerve cell processes have been reported as forming tight junctions which cannot be interpreted as synaptic contacts 260) this anomalous observation clearly requires confirmation. 

The dominating feature in the process of establishment is the morphology of the scolex. In the Pseudophyllidea, this can vary from a structure that is little more than a shallow groove - as in Schistocephalus or Ligula - to a well-developed bothrium, as in Diphyllobothrium spp., which, when... 

An alternative approach to studying the migration phenomenon has been adopted by Hopkins Allen (333). These workers severed the scolex of worms (one-worm infections) on day 14, without disturbing the attached scolex from the mucosa. They found that, within 48-72 h, the scolex had moved back to a position where a young worm of that size would normally be found. They suggested that the position of the scolex is, in part, determined by the position of the strobila, which monitors information about its position from all over its surface, balancing the input of adverse information from its tail and head ends (333). They concluded that the preferred site for H. diminuta was 30-50% down the small intestine. 

Fig. 10.4. Potential development of a protoscolex of Echinococcus granulosus or E. multilocularis in different habitats. 1, In the dog gut, the scolex evaginates, the organism attaches to the mucosa, differentiates in a strobilar direction and develops into an adult tapeworm. 2, In vivo, if a hydatid cyst bursts or leaks (as during a surgical operation) each protoscolex can differentiate in a cystic direction and form a (secondary) hydatid cyst. (After Smyth, 1987b.)...

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. 

Anderson, K. I. (1975a). Ultrastructure studies on Diphyllobothrium ditremum and D. dendriticum (Cestoda, Pseudophyllidea), with emphasis on the scolex tegument and the tegument in the area around the gential atrium. Zeitschrift fur Parasitenkunde, 46 253-64. 

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