Difference between revisions of "Tapeworm" - New World Encyclopedia
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In [[biology]], '''tapeworms''' or '''cestodes''' comprise a class ('''Cestoda''') of ribbon–like [[parasite|endoparasitic]] [[flatworm]]s that that live in the [[digestive tract]] of [[vertebrate]]s as adults and often in the bodies of various animals (intermediate hosts) as juveniles. | In [[biology]], '''tapeworms''' or '''cestodes''' comprise a class ('''Cestoda''') of ribbon–like [[parasite|endoparasitic]] [[flatworm]]s that that live in the [[digestive tract]] of [[vertebrate]]s as adults and often in the bodies of various animals (intermediate hosts) as juveniles. | ||
| − | + | ==Overview== | |
| − | + | As flatworms (phlum [[Platyhelminthes]]), the soft flatworm body is ribbon-shaped, flattened flattened dorso-ventrally (from top to bottom), and [[symmetry (biology)#Bilaterial symmetry|bilaterally symmetric]]. They are acoelomates that are characterized by having three germ layers (ectoderm, mesoderm, and endoderm) and lacking [[respiratory system|respiratory]] and [[circulatory system|circulatory]] systems. | |
| − | + | Cestoda is one of four classes of flatworms, the others being Trematoda ([[fluke]]s), [[Monogenea]]*, and [[Turbellaria]]*. While turbellarians, such as [[planaria]]s, tend to be free-living, the cestodes, trematodes, and monogeneans live as parasites in or on other animals. | |
| − | == | + | Cestodes are covered with a cuticle (tough but flexible, non-mineral covering), and lack a true [[circulatory system|circulatory]] or [[respiratory system]]; they do have a bilateral [[nervous system]]. |
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| + | 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 (an order of Eucestoda) are the most important to [[human]]s because they infect people, pets, and [[livestock]]. Among them, four significant genera are ''Taenia'', ''Diphyllobothrium'', ''Echinococcus'', and ''Hymenolepis''. | ||
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| + | In a [[#tapeworm infestation|tapeworm infection]], adult worms absorb food predigested by the host, so the worms have no need for a [[digestive tract]] or a mouth. Even large tapeworms are made almost entirely of reproductive structures with a small "head" for attachment. | ||
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| + | Tapeworms can grow 15 to 30 feet (10 meters) in length. The largest tapeworms grow up to 60 feet (Kimball 2006). Most tapeworms enter humans through contaminated food, the same way they enter secondary hosts like [[flea]], [[pig]], [[cattle]], and so forth. | ||
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| + | ==Tapeworm infestations== | ||
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| + | Adult tapeworm infection is the infection of the digestive tract by [[parasite|parasitic]] cestodes or tapeworms. Tapeworm larvae are sometimes ingested by consuming undercooked food. Once inside the digestive tract, the larva grows into an adult tapeworm, which can live for years and grow very large. Additionally, many tapeworm larvae cause symptoms in an intermediate host. For example, cysticercosis is a [[disease]] of humans involving larval tapeworms in the human body. | ||
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| + | Symptoms vary widely, depending on the species causing the infection. | ||
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| + | Tapeworms harm their host by stealing vital nutrients, causing [[malnutrition]], and anaemia; multiple infection can cause [[intestinal blockage]]s. The disease caused by the worm in human beings is generally known as '''cestodiasis'''. Symptoms vary widely, depending on the species causing the infection, from simple upper abdominal discomfort and diarrhea to serious nervous disorders caused by toxin of the parasite. However, infestations are usually [[asymptomatic]]. Gravid proglottides (worm segments) or eggs may be found in the [[stool]] of an infected person. | ||
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| + | Among the most common tapeworms in humans are the pork tapeworm, the beef tapeworm, the fish tapeworm, and the dwarf tapeworm. Infections involving the pork and beef tapeworms are also called '''taeniasis'''. | ||
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| + | ''Taenia solium'' and ''Taenia saginata'' are common tapeworms. A person can become infected by these parasites by eating rare 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. | ||
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| + | A dangerous complication of the parasite ''Taenia solium'', Cysticercosis, 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. | ||
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| + | A third type of tapeworm, ''Diphyllobothrium latum'', is contracted by eating raw, infected [[fish]]. The fish become infected by eating infected [[crustacean]]s, which became infected by consuming untreated sewage. This tapeworm results in symptoms similar to those of ''Taenia saginata'' and ''Taenia solium'', but can also include weakness and fatigue. [http://www.healthline.com/galecontent/tapeworm-diseases] | ||
''Taenia solium'' (pork tapeworm) and ''T. saginata'' (beef tapeworm) are the most common tapeworms of human beings. Their larval stage occurring intermediate hosts are pig and cattle respectively. A person can become infected by these parasites on consuming raw or undercooked meat (measly pork or beef) that has been infected by their larvae ('''cysticercus'''). The beef tapeworm is longer than pork tapeworm and lack rostellum as well as hooks on the scolex. Sometimes, these parasites may leave the usual digestive tract and migrate to the appendix, pancreas, or bile duct causing severe Sean Mullenish Diarrhea. | ''Taenia solium'' (pork tapeworm) and ''T. saginata'' (beef tapeworm) are the most common tapeworms of human beings. Their larval stage occurring intermediate hosts are pig and cattle respectively. A person can become infected by these parasites on consuming raw or undercooked meat (measly pork or beef) that has been infected by their larvae ('''cysticercus'''). The beef tapeworm is longer than pork tapeworm and lack rostellum as well as hooks on the scolex. Sometimes, these parasites may leave the usual digestive tract and migrate to the appendix, pancreas, or bile duct causing severe Sean Mullenish Diarrhea. | ||
Revision as of 17:28, 18 May 2007
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 Scolex of Taenia solium
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Subclass Cestodaria |
In biology, tapeworms or cestodes comprise a class (Cestoda) of ribbon–like endoparasitic flatworms that that live in the digestive tract of vertebrates as adults and often in the bodies of various animals (intermediate hosts) as juveniles.
Overview
As flatworms (phlum Platyhelminthes), the soft flatworm body is ribbon-shaped, flattened flattened dorso-ventrally (from top to bottom), and bilaterally symmetric. They are acoelomates that are characterized by having three germ layers (ectoderm, mesoderm, and endoderm) and lacking respiratory and circulatory systems.
Cestoda is one of four classes of flatworms, the others being Trematoda (flukes), Monogenea, and Turbellaria. While turbellarians, such as planarias, tend to be free-living, the cestodes, trematodes, and monogeneans live as parasites in or on other animals.
Cestodes are covered with a cuticle (tough but flexible, non-mineral covering), and lack a true circulatory or respiratory system; they do have a bilateral nervous system.
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 (an order of Eucestoda) are the most important to humans because they infect people, pets, and livestock. Among them, four significant genera are Taenia, Diphyllobothrium, Echinococcus, and Hymenolepis.
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. Even large tapeworms are made almost entirely of reproductive structures with a small "head" for attachment.
Tapeworms can grow 15 to 30 feet (10 meters) in length. The largest tapeworms grow up to 60 feet (Kimball 2006). Most tapeworms enter humans through contaminated food, the same way they enter secondary hosts like flea, pig, cattle, and so forth.
Tapeworm infestations
Adult tapeworm infection is the infection of the digestive tract by parasitic cestodes or tapeworms. Tapeworm larvae are sometimes ingested by consuming undercooked food. Once inside the digestive tract, the larva grows into an adult tapeworm, which can live for years and grow very large. Additionally, many tapeworm larvae cause symptoms in an intermediate host. For example, cysticercosis is a disease of humans involving larval tapeworms in the human body.
Symptoms vary widely, depending on the species causing the infection.
Tapeworms harm their host by stealing vital nutrients, causing malnutrition, and anaemia; multiple infection can cause intestinal blockages. The disease caused by the worm in human beings is generally known as cestodiasis. Symptoms vary widely, depending on the species causing the infection, from simple upper abdominal discomfort and diarrhea to serious nervous disorders caused by toxin of the parasite. However, infestations are usually asymptomatic. Gravid proglottides (worm segments) or eggs may be found in the stool of an infected person.
Among the most common tapeworms in humans are the pork tapeworm, the beef tapeworm, the fish tapeworm, and the dwarf tapeworm. Infections involving the pork and beef tapeworms are also called taeniasis.
Taenia solium and Taenia saginata are common tapeworms. A person can become infected by these parasites by eating rare 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.
A dangerous complication of the parasite Taenia solium, Cysticercosis, 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 Taenia saginata and Taenia solium, but can also include weakness and fatigue. [1]
Taenia solium (pork tapeworm) and T. saginata (beef tapeworm) are the most common tapeworms of human beings. Their larval stage occurring intermediate hosts are pig and cattle respectively. A person can become infected by these parasites on consuming raw or undercooked meat (measly pork or beef) that has been infected by their larvae (cysticercus). The beef tapeworm is longer than pork tapeworm and lack rostellum as well as hooks on the scolex. Sometimes, these parasites may leave the usual digestive tract and migrate to the appendix, pancreas, or bile duct causing severe Sean Mullenish Diarrhea.
A dangerous complication of the parasite T. solium, Cysticercosis, may occur if due to reverse peristalsis auto–infection takes place or the person as the secondary host comes to ingest onchosphore larvae in contaminated food and the larvae develop outside the intestinal tract. The released hexacanth larvae 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 (Merck 2005).
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 T. solium, but can also include weakness and fatigue.
The hydatid worm, Echinococcus granulosus is a parasite of dog, cat, and so forth; and its intermediate host is cattle. However, humans may happen to ingest its onchophore larvae in contaminated food and drink or because of careless association with infected dogs and cats. Most harm is done by cysticercus larvae that develop in liver, lung, and in a few cases in brain, heart, bone marrow, kidney, spleen, muscles, and so forth. by forming water bladder or hydatid cyst. A hydatid cyst may grow upto football size in 12 to 20 years in man, necessitating surgery.
Another common tapeworm of human beings is dwarf tapeworm, Hymenolepis nana. Same host serves for the development of larvae (cysticercus) and the adult without requiring intermediate host (monogenetic condition), however, certain rat fleas and beetles may work as intermediate host to facilitate the propagation of the parasite. In the monogenetic condition, onchophore larvae are ingested in contaminated food, released hexacanth larvae penetrate mucosa of villi, cysticercoid larvae develop in the villi, and re–enter the lumen by rupture of villi. Due to auto–infection, cysticercoids attach themselves to the mucosa among the villi and develop into adults. This parasitism is asymptomatic unless there is heavy infection.
Adult morphology
Basically, adults of all tapeworms have same body structure consisting of a scolex, sometimes colloquially referred to as the "head," a neck, and a strobila made of a few to large number of proglottids, which are sometimes called "segments." These parasites are given the name "tapeworm," because their strobila look like a strip of tape. As mentioned above, the pre–digested food in the host's small intestine is the chief source of nourishment for tapeworm. The general body surface of the parasite is greatly increased by the presence of microvilli. Therefore, the swift efficiency with which absorption takes place can be compared with the soaking action of blotting paper. Respiration of the tapeworms being mainly anaerobic or anoxybiotic and glycolysis being the chief respiratory pathway, the parasites lack respiratory organs too. When Oxygen become available, general body lining works as the respiratory surface. All cestodes have nerve rings and lateral nerve cords passing through out the length of the body. Their main excretory units are protonephric flame cells scattered all over the parenchyma of the body. The filtered excretory material is emptied into lateral longitudinal excretory canals extending the whole length of the body and thrown out through excretory pore at the end of the body.
Scolex
The Scolex or "head" is the anterior end of the worm and remain attached to the intestine of the definitive host. It is not bigger than the head of a pin, still it works as the hold–fast of the parasite. 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 to help in attachment. Cyclophyllid cestodes can be identified by the presence of four suckers on their scolex, though they may have rostellum and hooks.
Though the scolex is often the most distinctive part of an adult tapeworm, diagnosis is carried out by identifying eggs and gravid proglottids in feces, as it remains hidden inside the patient.
Neck
The Neck of tapeworm is a well–defined, short, narrow, and unsegmented region behind scolex. It is dorso–ventrally flattened and composed of a relatively undifferentiated mass of cells. It is the budding zone, growth zone, area of proliferation or area of segmentation, as it is here that new proglottids are formed.
Strobila
The strobila forms the main bulk of the body and is composed of a linear series of segments or proglottids arranged in a chain–like fashion. The number of proglottids varies from three in E. granulosus to 2,000 in T. saginata. However, they can be grouped into three different kinds, namely immature, mature, and gravid proglottids.
Immature Proglottids are the anterior most one just behind the neck. They are shorter and broader and are devoid of reproductive organs.
Mature Proglottids occupy the middle part of the strobila and are squarish in outline. Tapeworms are hermaphrodite (male and female sex organs in the same individual) and protandrous (male maturing first), therefore, anterior mature proglottids consists of only male reproductive organs, while the posterior ones contain both male and female organs side by side. Thus a mature proglottid is a complete reproductive unit and produces eggs either by self–fertilization or cross–fertilization with other mature proglottids. It has been suggested by some early biologists that each should be considered a single organism, and that the tapeworm is actually a colony of proglottids.
gravid proglottids occur in the posterior part of strobila and are longer than the width. These proglottids consist of no more reproductive organs excepting the highly branched uterus packed with fertilized eggs at different stages of development. The terminal gravid proglottids detach from rest of the body either singly (e.g., T. saginata) or in small group (e.g., T. solium) by a process termed apolysis. This phenomenon serves to limit the length of the parasite and to transfer the developing embryo to exterior in feces of the host.
Life Cycle
Excepting a few, most tapeworms are digenetic, completing adult stage and sexual reproduction in primary host and larval stage in secondary host. The break off gravid proglottids contain thousands of fertilized eggs with onchosphere larvae. On reaching ground, proglottids eventually disintegrate and the larvae are set free. The secondary hosts (pig for T. solium, and cow and buffalo for T. saginata) become infected on consuming food contaminated with the larvae. In the stomach of the secondary host, the larvae lose their protective sheath due to the proteolytic enzymes and the hooked hexacanth larvae hatch out. Hexacanths pierce the mucosa of the intestine to enter blood stream and make a voyage through different organs of the body finally to land in the striped muscle of the host. They settle there to develop into bladder–worm or cysticercus. Feeding on such infected meat without proper cooking leads to the entry of the parasite into the primary host. Cysticercus become active in the small intestine, develop scolex, and transform into miniature for of the adult tapeworm. With the help of scolex, they remains attach to the intestinal mucosa in between the villi and repeat the cycle.
Treatment
CDC guidelines for treatment is a prescription drug called praziquantel. Praziquantel is generally well tolerated. Other effective drugs are mepacrine (Atebrin), diclorophen, and yamesan. Sometimes more than one treatment is necessary (CDC 2004).
As both primary and secondary hosts are infected via dietary means, personal and community level sanitation as well as the sanitation of domestic and pet animals are to be considered with priority. At the same time, careful inspection of meat at the slaughter houses, avoiding of measly pork and measly beef, avoiding of raw or undercooked meat, proper sanitary control of sewage disposal have to be practiced (MyoClinic 2006). Template:CDC
Reference
Campbell, N.A., Reece, J.B., and Mitchell, L.G. Biology. Benjamin–Cummings Pub. 1999 ISBN 0805330445
CDC.2004. Hymenolepis Infection. Parasitic Disease Information Fact Sheet, Division of Parasitic Diseases. Retrieved May 8, 2007
Kimball, J.W. 2006.Tapeworms (cestoda). Kimball's Biology Pages. Retrieved May 8, 2007.
MayoClinic. 2006. Tapeworm Infection. Infectious Diseases. Retrieved May 8, 2007.
Merck. 2005. Tapeworm Infection. The Merck Manuals of Medication Information. Second Home Edition. Online Version. Retrieved May 8, 2007.
See also
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