tapeworm
tape·worm
T0043300 (tāp′wûrm′)tapeworm
(ˈteɪpˌwɜːm)tape•worm
(ˈteɪpˌwɜrm)n.
tape·worm
(tāp′wûrm′)| Noun | 1. |  tapeworm - ribbonlike flatworms that are parasitic in the intestines of humans and other vertebrates |
n.
tapeworm
tapeworm,
name for the parasitic flatworms forming the class Cestoda. All tapeworms spend the adult phase of their lives as parasites in the gut of a vertebrate animal (called the primary host). Most tapeworms spend part of their life cycle in the tissues of one or more other animals (called intermediate hosts), which may be vertebrates or arthropods.Anatomy and Function
An adult tapeworm consists of a knoblike head, or scolex, equipped with hooks for attaching to the intestinal wall of the host (which may be a human), a neck region, and a series of flat, rectangular body segments, or proglottids, generated by the neck. The chain of proglottids may reach a length of 15 or 20 ft (4.6–6.1 m). Terminal proglottids break off and are excreted in the feces of the host, but new ones are constantly formed at the anterior end of the worm. As long as the scolex and neck are intact the worm is alive and capable of growth. A rudimentary nervous system and excretory system run the length of the worm, through the proglottids. However, there is no digestive tract; the worm absorbs the host's digested food through its cuticle, or outer covering.
Reproduction
Each proglottid contains a complete set of male and female reproductive organs that produce the sex cells. Fertilization is internal; in most species cross fertilization between two adjacent worms is necessary, but in a few species self-fertilization may occur between two proglottids of the same worm, or within the same proglottid. In some species the fertilized eggs are shed continuously and leave the host's body in the feces; in others the fertilized eggs are stored until the proglottid is filled with them and the entire proglottid is then shed. The eggs develop into embryos with a hard outer shell; these do not hatch until they are eaten by a suitable intermediate host.
Humans as Tapeworm Hosts
Human tapeworm infestations are most common in regions where there is fecal contamination of soil and water and where meat and fish are eaten raw or lightly cooked. In the case of the human tapeworm most common in the United States (the beef tapeworm, Taenia saginata) the usual intermediate host is a cow, which ingests the proglottid while drinking or grazing. The round-bodied embryos, equipped with sharp hooks, hatch and bore through the cow's intestinal wall into the bloodstream, where they are carried to the muscles. Here each embryo encloses itself in a cyst, or bladder; at this stage it is called a bladder worm. During the bladder worm stage the embryo develops into a miniature scolex; it remains encysted until the muscle is eaten by a primary host, in this case a human. If the scolex has not been killed by sufficient cooking of the meat, it sheds its covering and attaches to the intestinal wall, where it begins producing proglottids.
A human tapeworm common in Mexico, the pork tapeworm (T. solium), has a similar life cycle, with a pig as the usual intermediate host. The fish tapeworm, Diphyllobothrium latum, transmitted to humans from fish, especially pike, is common in Asia and in Canada and the northern lake regions of the United States. This tapeworm has a more elaborate life cycle, involving both a fish and a crustacean as intermediate hosts. The dwarf tapeworm, Hymenolepsis nana, is transmitted through fecal contamination and is common in children in the southeastern United States. There are also several tapeworms for whom humans are the usual intermediate host; among these, the dog tapeworm, Echinococcus granulosis, spends its adult phase in the intestines of dogs.
Consequences of Infestation
Intestinal tapeworm infestation frequently occurs without symptoms; occasionally there is abdominal discomfort, diarrhea, constipation, or weight loss. The presence of tapeworm proglottids in clothing, bedding, or feces is the usual sign of infestation. Treatment is typically with albendazole or praziquantel, which kill the worm.
The most serious tapeworm infestation in humans is caused by the ingestion of T. solium eggs through fecal contamination, which results in the person serving as the intermediate, rather than the primary, host. The embryos migrate throughout the body, producing serious illness if they lodge in the central nervous system. In many poorer regions of the world, the larvae of T. solium are a major cause of human epilepsy. The embryos of the dog tapeworm encyst in various internal organs of humans, most commonly in the liver. The cysts produced by these embryos are called hydatid cysts, and the infestation of the liver is called hydatid disease.
Classification
Tapeworms are classified in the phylum PlatyhelminthesPlatyhelminthes
, phylum containing about 20,000 species of soft-bodied, bilaterally symmetrical, invertebrate animals, commonly called flatworms. There are four classes: the free-living, primarily aquatic class, Turbellaria, and Trematoda, Cestoda, and Monogenea, which are
..... Click the link for more information. , class Cestoda.
tapeworm
[′tāp‚wərm]tapeworm
tapeworm
tapeworm
[tāp´werm]Although a large variety of adult tapeworms are sometimes human parasites, only a few infect humans to any great degree. Taenia saginata, the beef tapeworm, and T. solium, the pork tapeworm, are widespread and quite common. Beef tapeworms grow to a length of 4 to 8 meters (12 to 25 feet), and adult pork tapeworms average 2 to 4 meters (6 to 12 feet) in length. Both species release white, egg-containing proglottids, or segments of the body, which make their way to the anus and may be found in clothes or bedding. Diphyllobothrium latum, the fish tapeworm, is found in North America in the Great Lakes region, as well as in Northern Europe and Japan; it may grow as long as 18 meters (60 feet). Hymenolepis nana and H. diminuta are dwarf tapeworms that are common in the tropics and subtropics.
The diagnosis of a tapeworm infection is made when segments of the worm are found in clothing or bedding or when characteristic eggs or segments are found in the stool. Occasionally diarrhea, vague abdominal cramps, flatulence, distention, and nausea occur. Mental deterioration and seizures are rare complications, occurring only when larval forms of the worm invade brain tissue. Tapeworm infection can be prevented by cooking pork, beef, and fish properly. Although most meats and fish are inspected under government supervision, eggs and larvae are not always detectable; the only certain protection is proper cooking.
Once it is inside the body, the tapeworm can be eliminated by specific anthelmintic drugs or surgery. The drug of choice is usually praziquantel, which should be given in a dose large enough to cause the worm to release its hold and pass out through the intestinal tract. If the head is found in the evacuated feces, no further treatment is necessary. However, if the head is not found, the worm could regenerate in two to three months, with segments reappearing in the stools.
Echinococcus granulosus and E. multilocularis differ from other tapeworms in that the adults infect animal hosts and the larval forms are found in humans. The larvae develop in the human intestine, penetrate its wall, and are carried by the lymphatics to various organs of the body where they form slowly growing cysts (cysts" >hydatid cysts). The liver is the organ most commonly involved. Treatment is by surgical removal of the cyst. Infection with this worm (echinococcosis or hydatid disease) is uncommon in the United States.
tape·worm
(tāp'wŏrm),tapeworm
(tāp′wûrm′)tape·worm
(tāp'wŏrm)tapeworm
A ribbon-like population, or colony, of joined flatworms, of the class Cestoda , derived from a common head (scolex) equipped with hooks or suckers by which it is attached to the lining of the intestine. Each segment, of which there may be a thousand, is called a proglottid and each contains both male and female reproductive organs. The younger, smaller proglottids release sperms which fertilize the eggs in the older, larger, proglottids. Fertilized segments break off and are passed in the faeces. If these are eaten by an animal (the intermediate host), the larvae develop, travel to the animal's muscles and form cysts, and if such animal meat is eaten, undercooked, the worm is released in the intestine, attaches itself, and the life cycle is continued. Tapeworms can be eliminated with anthelmintic drugs.tapeworm
any parasitic flatworm of the class Cestoda (phylum Platyhelminthes). The adults attach themselves inside the gut system of vertebrates by means of hooks and suckers on the SCOLEX, and the long, ribbonlike body made up of a series of proglottides,may reach a length in excess of 10 m in some species. Eggs develop into 6-hooked embryos and pass out with the FAECES of the host, and if eaten by a suitable secondary host, develop into a larval stage called a CYSTICERCUS. When eaten by the primary host, (which may take place in some species only after transfer through a second secondary host) the tapeworm becomes sexually mature.Tapeworm
tapeworm
- noun
Synonyms for tapeworm
noun ribbonlike flatworms that are parasitic in the intestines of humans and other vertebrates
Synonyms
- cestode
Related Words
- flatworm
- platyhelminth
- Cestoda
- class Cestoda
- echinococcus
- taenia
- portio vaginalis cervicis
- radioactive chain
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