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 Scolex of Taenia solium
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Subclass Cestodaria |
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.
Contents |
Overview
Authors Craig and Ito, in Intestinal Cestodes, describe the gut-dwelling worm as segmented and band-like (Cestoda) in its adult stage (Craig & Ito 2007:524). Its first stage in tissues and organs of vertebrates or 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 (Craig and Ito 2007:524).
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 don't show any signs of illness (Craig & Ito 2007:524). 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 it in undergarments (Craig and Ito 2007: 524).
Life cycle
The life cycle of a tapeworm starts with a human eating undercooked, infected meat. The tapeworm will then grow and release small packages of fertilized eggs and sperm. These packages are excreted by the host. If they happen to land in grass, for instance, the package will open. By that time, the tape worm eggs will have developed. The eggs are released onto the grass. If a cow were to eat that grass, the eggs would become larvae and burrow into the cow's muscle. If that cow was eaten without being cooked thoroughly, the whole cycle would start again.
Scolex
The scolex, or "head" of the worm, attaches to the intestine of the definitive host. In some groups, the scolex is dominated by bothria, which are sometimes called "sucking grooves," and function like suction cups. Other groups 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 eminate from the commissures to supply the general body muscular and sensory ending.1 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.1
Proglottids
The body is composed of successive units posterior to the scolex, called the 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 mature 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.
Pathology
According to Intestinal Cestodes, authors Craig and Ito 2007 suggest that the effects of cestodes are usually very minimal. Those who are infected often describe the following symptoms: abdominal discomfort and pain, cramps, colic, flatulence, diarrhea, constipation, nausea, dizziness, vomiting, restlessness, vertigo, headache, tiredness, malabsorption, anorexia, muscular pain, vitamin deficiency, megaloblastic anemia, weight loss (or gain), intestinal blockage, jejunal perforation, appendicitis, pancreatitis, pseudo-incontinence, pruritis ani, rectal-flutters, spontaneous voiding of segments from the anus, depression and psychosis (Craig & Ito 2007:524). In the past, through self-infection of Taenia Solium (the pork tapeworm) there have been serious life-threatening infections of taeniais (also referred to as taeniosis) which increase the chances of neurocysticercosis (Craig & Ito 2007: 524).
Additional facts
A 100-foot tapeworm was found in the intestine of a whale captured off Catalina Island.[1]
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 contains material from the CDC (Center for Disease Control) website which, as a U.S. government publication, is in the public domain.
- Craig,Philip & Ito, Akira (2007). "Intestinal Cestodes". Current Opinion in Infectious Diseases 20: 524-532.
External links
- How Disgusting are Tapeworms? Article from TalktotheVet.com
Wikipedia content modification information:
- This page was last modified on 3 September 2008, at 04:09.
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