Cestoda

For the musical collaboration named Tapeworm, see Tapeworm (band).

Tapeworm is also an older name for a type of computer virus.

Cestoda
File:Tenia solium scolex.jpg
Scolex of Taenia solium
Scientific classification
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Superphylum:	Platyzoa
(unranked):	Bilateria
Phylum:	Platyhelminthes
Class:	Cestoda
Orders
Subclass Cestodaria: Amphilinidea Gyrocotylidea Subclass Eucestoda: Aporidea Caryophyllidea Cyclophyllidea Diphyllidea Lecanicephalidea Litobothridea Nippotaeniidea Proteocephalidea Pseudophyllidea Spathebothriidea Tetraphyllidea Trypanorhyncha

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. Taenia saginata, the beef tapeworm, can grow up to 40 feet long (12 m); other species may grow to over 100 feet (30 m).

Overview

Researchers describe the gut-dwelling worm as 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 (or metacestode). tapeworms are not good.

Anatomy

Scolex

The worm's scolex ("head") 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. Cyclophyllid cestodes can be identified by the presence of four suckers on their scolex. Tapeworms have sharp hooks on one side of the head which dig into the lining of the host's intestine.

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 feces is important.

Muscular system

The main nerve centre of a cestode is in its scolex; as a cerebral ganglion. 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. Some nerves are only temporary. These are in the proglottids, and stop working with a detach.

Proglottids

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), located in the proglottids, for excretion.

Mature proglottids are released from the tapeworm's posterior end and leave the host in feces.

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.

Life cycle

Many tapeworms have a two-phase life cycle with two types of host. The adult taenia saginata, for example lives in the gut of a primate such as a human. Proglottids leave the body through the anus and fall onto the ground, where they may be eaten with grass by animals such as cows. In the cow's body the juvenile forms migrate and establish themselves as cysts in body tissues such as muscles, rather than the gut; they cause more damage to this host than the intestinal form to its host. The parasite completes its life cycle when the grass-eater is eaten by a compatible carnivore—possibly a human with a preference for rare meat—in whose gut the adult taenia establishes itself. While being treated for certain tapeworm infections, you can reinfect yourself by ingesting tapeworm eggs shed by the adult worm into your stool.

Taxonomy

There are fourteen recognised orders of Cestodes: the Amphilinidea, Gyrocotylidea and 12 orders belonging to the Eucestoda. Within the Eucestoda the Spathebothriidea appear to be a sister group to the remaining 11 orders. The Pseudophyllidea and Haplobothriidea appear to form a clade as do Cyclophyllidea, Nippotaeniidea and Tetrabothriidea.

See also

• Diphyllobothrium (Fish tapeworm)
• Cysticercosis
• List of parasites (human)
• Tapeworm infection

References

• Campbell, Reece, and Mitchell, Biology, 1999
• Merck Manual of Medication Information, Second Home Edition, Online Version, Tapeworm Infection 2005
• Mayo Clinic Website on infectious diseases, Mayo Clinic - Tapeworm Infection, 2006
• Medline Plus - Taeniasis (tapeworm infection)
• University of South Carolina - School of Medicine - CESTODES (TAPE WORMS)

 This article incorporates public domain material from websites or documents of the Centers for Disease Control and Prevention.

External links

• How Disgusting are Tapeworms? Article from TalktotheVet.com