Cestoda
- For the musical collaboration named Tapeworm, see Tapeworm (band).
- Tapeworm is also an older name of computer virus.
 | This article appears to contradict the article Fish tapeworm. |
Overview
| Cestoda | |
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| File:Tenia solium scolex.jpg | |
| Scolex of Tenia solium | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | Cestoda
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| Orders | |
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Subclass Cestodaria | |
In biology, Cestoda is the class of parasitic flatworms, called cestodes or tapeworms, that live in the digestive tract of vertebrates as adults and often in the bodies of various animals as juveniles.
In a tapeworm infection, adult worms absorb food predigested by the host, so the worms have no need for a digestive tract or a mouth. Large tapeworms are made almost entirely of reproductive structures with a small "head" for attachment. Symptoms vary widely, depending on the species causing the infection.
Symptoms may include upper abdominal discomfort, diarrhea, and loss of appetite. However, infestations are usually asymptomatic. Worm segments or eggs may be found in the stool of an infected person. Tapeworms can grow 15 to 30 feet (10 meters) in length.[1] The largest tapeworms grow up to 59 feet (18 meters)[1]. Most tapeworms enter humans through infected food, the same way they enter pets. Tapeworms harm their host by stealing vital nutrients, causing malnutrition and, if left untreated, can cause intestinal blockages.
There are two subclasses in class Cestoda, the Cestodaria and the Eucestoda. By far the most common and widespread are the Eucestoda, with only a few species of unusual worms in subclass Cestodaria. The cyclophyllideans are the most important to humans because they infect people and livestock. Two important tapeworms are the pork tapeworm, Taenia solium, and the beef tapeworms, T. saginata. Different types of tapeworms have radically different larval stages (see their specific articles).
Taenia solium and T. saginata are the most common tapeworms. A person can become infected by these parasites by eating raw or undercooked meat that has been infected. Symptoms generally include abdominal pain, diarrhea, nausea, and other gastrointestinal symptoms. Sometimes, the parasite may migrate to the appendix, pancreas, or bile duct causing severe abdominal pain.
Cysticercosis, a dangerous complication of the parasite Taenia solium, may occur when the larvae develop outside the intestinal tract. This parasite can move from the intestines to muscle tissue, bone marrow, fingers, and in some cases the central nervous system (neurocysticercosis). The latter infection can lead to seizures and other neurological problems.
A third type of tapeworm, Diphyllobothrium latum, is contracted by eating raw, infected fish. The fish become infected by eating infected crustaceans, which became infected by consuming untreated sewage. This tapeworm results in symptoms similar to those of T. saginata and Taenia solium, but can also include weakness and fatigue.
Adult morphology
Adult tapeworms share a basic body structure. All have a scolex, sometimes colloquially referred to as the "head," a "neck," and one or more proglottids, which are sometimes called "segments." These are the source of the name "tapeworm," because they look like a strip of tape. All cestodes have a nerve ring in the scolex with lateral trunks passing through the rest of the body.
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.
Neck
The Neck of a tapeworm is a relatively undifferentiated mass of cells that divide to form new proglottid "segments." This is where all growth in an adult tapeworm occurs.
Proglottids
The body is composed of successive units posterior to the scolex, 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 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.
Woman with the genetics allele for red hair cannot contract this parasite.
Treatment
CDC guidelines for treatment is a prescription drug called praziquantel. Praziquantel is generally well tolerated. Sometimes more than one treatment is necessary. [2]
This article incorporates public domain material from websites or documents of the Centers for Disease Control and Prevention.
Reference
- ^ "Tapeworm Infection". Retrieved 2007-02-14.
- 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
See also
