Cestoda

Tapeworm is also an older name for a type of computer virus.
Cestoda
Scolex of Taenia solium
Scolex of Taenia solium
Scientific classification
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Platyzoa
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).[1]

Contents

Overview

Craig and Ito describe the gut-dwelling worm as segmented and band-like in its adult stage.[2] Its first stage in tissues and organs of vertebrates, including humans, is the growth of a cyst-like juvenile (or metacestode). The potential cause of illness and disease is due to a metacestode stage happening in human tissues, rather than an adult tapeworm.[2]

The tegument is the body surface of the adult tapeworm. 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.[2] A carrier can notice the segments (proglottides) when using the bathroom, for instance, in the feces in a toilet bowl. Because tapeworms move around constantly, one may find them in undergarments.[2] In previous times in history, people wishing to lose weight have purposely ingested tapeworms to aid in weight loss dieting.

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, though they may have other structures.

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 center 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.

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) for excretion, which are located in the proglottids.

Mature or gravid proglottids are released from the tapeworm and leave the host in its 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.

See also

Footnotes

  1. ↑ "The Persistent Parasites". Time Magazine (Time Inc). 1957-04-08. http://www.time.com/time/magazine/article/0,9171,809356-1,00.html. 
  2. ↑ 2.0 2.1 2.2 2.3 Philip Craig; Akira Ito (October 2007). "Intestinal Cestodes". Current Opinion in Infectious Diseases 20 (5): 524–532. 

References

This article contains material from the CDC (Center for Disease Control) website which, as a U.S. government publication, is in the public domain.

External links