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Cestoda or the tapeworm
A tapeworm on the move
Cestoda is a class of parasitic flatworms, commonly called tapeworms that live in the digestive tract of vertebrates as adults and often in the bodies of various animals as juveniles.
Some species of this worm are said to be able to grow up to about 30 metres (100 feet) long.
The worm has been described by some researchers as the gut-dwelling worm which is segmented and band-like in its adult stage.
Its first stage in tissues and organs of vertebrates, including humans, is the growth of a cyst-like juvenile.
Tapeworms take the host’s nutrients and do not attack the mucosa of the small intestine or remove blood. Infections, therefore, are benign. Most often hosts do not show any signs of illness.
A carrier can notice the segments (proglottids) when using the bathroom, for instance, in the faeces in a toilet bowl. Because tapeworms move around constantly, one may find them in undergarments. In previous times in history, people wishing to lose weight have purposely ingested tapeworms to aid in weight loss dieting.
The worm’s head or scolex attaches to the intestine of the definitive host. In some species, the scolex is dominated by bothria, which are sometimes called ‘sucking grooves’, and function like suction cups. Other species have hooks and suckers that aid in attachment.
While the scolex is often the most distinctive part of an adult tapeworm, it is often unnoticed in a clinical setting as it is inside the patient. Thus, identifying eggs and proglottids in faeces is important.
The main nerve centre of a cestode is in its scolex. Motor and sensory innervation depends on the number and complexity of the scolex. Smaller nerves emanate from the commissures to supply the general body muscular and sensory ending.
The cirrus and vagina are innervated and sensory endings around the genital pore are more plentiful than other areas. Sensory function includes both tactoreception and chemoreception.
The body is composed of successive segments (proglottids). The sum of the proglottids is called a strobila, which is thin, resembling a strip of tape, and is the source of the common name ‘tapeworm’. Like some other flatworms, cestodes use flame cells (protonephridia) for excretion, which are located in the proglottids.
Mature or gravid proglottids are released from the tapeworm and leave the host in its faeces. Because each proglottid contains the male and female reproductive structures, they can reproduce independently. It has been suggested by some biologists that each should be considered a single organism, and that the tapeworm is actually a colony of proglottids.
The layout of proglottids comes in two forms, craspedote, meaning proglottids are overlapped by the previous proglottid and acraspedote which indicates a non-overlapping conjoined proglottid.
Adult tapeworm is the infection of the digestive tract by parasitic flatworms called cestodes or tapeworms. Live tapeworm larvae are sometimes ingested by consuming undercooked food. Once inside the digestive tract, the larva grows into an adult tapeworm and grows very large. Additionally, many tapeworm larvae cause symptoms in an intermediate host. For example, cysticercosis is a disease of humans involving larval tapeworms in the human body.
Among the most common tapeworms in humans are the pork tapeworm, the beef tapeworm, the fish tapeworm, and the dwarf tapeworm. Infections involving the pork and beef tapeworms are also called taeniasis. Tapeworms of the genus Echinococcus also infect animals and humans, and cause the most harm to intermediate hosts such as sheep and cattle. Infection with this type of tapeworm is referred to as Echinococcosis or hydatid disease.
With a few notable exceptions like the fish tapeworm, most cestodes that infect humans and livestock are cyclophyllids, and can be identified as such by the presence of four suckers on their scolex or head.
(Source: Wikipedia – The Free Online Encyclopedia)
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