Difference between revisions of "Fluke" - New World Encyclopedia
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| − | + | "Flukes" or "fatworms" is the common name applied to the flat, leaflet like endoparasites of [[class (biology)|class]] '''Trematoda''' within the [[phylum (biology)|phylum]] [[Platyhelminthes]]. This term can be traced back to the [[Anglo-Saxons|Saxon]] name for [[flounder]], and refers to the flattened, rhomboidal shape of the worms. | |
| − | + | All trematodes are [[parasite|parasitic]] flatworms. Previous classification systems included the [[Monogenea]] amongst the trematoda, alongside the [[Digenea]] and [[Aspidogastrea]], on the basis that they were all [[vermiform]] parasites. The taxonomy of the Platyhelminthes is being subjected to extensive revision, thanks to modern [[phylogenetics|phylogenetic]] studies; modern sources place the Monogenea in a separate class within the phylum. Moreover, there are no known cases of human infection with Aspidogastreans, therefore the use of the term "fluke" in relation to human beings refers solely to digeneans (require at least two hosts for the completion of their life cycle). | |
| − | All trematodes are [[parasite|parasitic]] flatworms. Previous classification systems included the [[Monogenea]] amongst the trematoda, alongside the [[Digenea]] and [[Aspidogastrea]], on the basis that they were all [[vermiform]] parasites. The taxonomy of the Platyhelminthes is being subjected to extensive revision thanks to modern [[phylogenetics|phylogenetic]] studies | ||
| − | == | + | ==Types of Flukes== |
| − | + | The flukes can be categorized into three groups on the basis of the systems they infect. '''Intestinal flukes''' occur attached to the mucosa of the intestine, some of the intestinal flukes infecting human beings are the species of genera ''Echinostoma'' ''Gastrodiscoides'', ''Heterophyes'', ''Metagonimus'', etc. Some '''zoonotic flukes''', e.g., ''Echinostoma ilocanum'' and ''Heterophyes heterophyes'' can infect human beings because of exposer, though their definitive hosts are other mammals like dog, cats, etc. '''Tissue flukes''' infect [[biological tissue]]s of liver, lungs or bile duct attaching themselves on their surface. Some of the flukes of this category are lung fluke, e.g., ''[[Paragonimus westermani]]'', and [[liver fluke]]s, e.g., ''[[Clonorchis|Clonorchis sinensis]]'', ''[[Fasciola hepatica]]'', ''Fasciolopsis buski'', ''Dicrocoelium spp.'', etc. The third category of flukes is known as '''blood flukes''', and inhabit the [[blood]] in some stages of their life cycle. Blood flukes include various species of the genus ''[[Schistosoma]]'' (''Bilharzia''), like ''S. japonicum'', ''S. mansoni'', ''S. haematobium'', etc. | |
| − | + | ==General Morphology== | |
| + | Flukes are laterally expanded to oval to oblong shape, and flattened dorso-ventrally into thin sheet. The unsegmented fluke body is covered by a tough cuticular tegument for its protection from digestive enzymes of the host. Anterior body end is produced into an oral cone for bearing an oral sucker with a centrally placed mouth. Posterior to this is a ventral sucker called '''acetabulum''' for strong attachment on the surface of the host organs. Alimentary canal is incomplete, as the intestine never open out via an anus. A small opening at the posterior end of the body is the common pore for protonephric excretory system. Most of the flukes are '''hermaphrodite''' having the organs of both sexes in a single individual. Although there is a common gonopore, cross fertilization is facilitated whenever possible. | ||
| + | Species of ''Schistosoma'' differ from other fluke in two major aspects: They are '''dioecious''' with well-defined sexual dimorphism. Their body is elongated, female being more slender, cylindrical and permanently lodged in the gynaecophoric canal of male. | ||
| − | + | ==Life Cycles== | |
| + | Flukes being mostly digenetic, have a complex [[biological life cycle|life cycle]], often involving several intermediate [[hosts]]. Depending on the types of the parasite, the eggs pass from the host with the [[feces]], sputum or the urine. When the eggs reach water, they hatch into free-swimming larvae called [[miracidia]]. The miracidia penetrate a specific fresh water [[snail]] or other [[mollusk|molluscan]] intermediate host to become second larvae called [[sporocyst]]s. The cells inside the sporocysts divide by [[mitosis]] to form ''redia'' larvae. Rediae, in turn, give rise to free-swimming larvae known as [[cercaria]]e, which escape from the mollusk into water again. In general case, the cercaria larvae burrow through exposed skin using [[enzymes]], penetrate another intermediate host (often an [[arthropod]] but can also be aquatic vegetation) and then en[[cyst]] as [[metacercaria]]e. When this host is eaten by the definitive host, the metacercariae excyst and develop into adult to repeat the life cycle. In case of ''Schistosoma'', cercaria larvae infect definitive host (man) by directly penetrating the skin while in water. For more information on life cycles, see the respective pages on [[Digenea]] and [[Aspidogastrea]]. | ||
| − | == | + | ==Pathogenicity== |
| − | + | Pathogenicity of the flukes varies with the sites of their infection. In the intestinal fluke, patient may show abdominal discomfort (diarrhea, nausea, vomiting, abdominal pain, ulceration) associated with the inflammation of the gut wall, as well as facial, abdominal and lower limb edema due to immune sensitization caused by the foreign proteins of the parasites. Among the tissue flukes, liver flukes cause liver abscesses, fibrosis, jaundice, and a type of hepatitis, while the Lung flukes produce symptoms similar to pulmonary tuberculosis. Infection of blood flukes causes fever and chills, but also elevates the number of white blood cells (eosinophils), as well as abdominal pain resulting from enlargements of the liver and spleen. Some parasitic trematodes [[chemical castration|chemically castrate]] their host. | |
| + | |||
| + | ==Treatments== | ||
| + | |||
| + | '''Medication''' is achieved generally by the use of different types of antimony containing drugs. They are effective against the flukes of all kinds. | ||
| + | |||
| + | '''Prophylaxis''' (preventive measures) includes personal hygiene, community sanitation, awareness campaign against toilet and sewage discharge in or near water resources, control of intermediate host, treatment of the infected persons and the pets, disinfection of contaminated water reservoirs, swimming pools, etc. | ||
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{{commons|Flukes}} | {{commons|Flukes}} | ||
| − | == | + | ==References== |
| − | |||
| + | *Gibson, D.I., Bray, R.A. & Jones, A., ''Keys to the Trematoda'', 3 Volumes ISBN 0851995470 | ||
{{credit1|Trematoda|113723353}} | {{credit1|Trematoda|113723353}} | ||
[[Category:Life sciences}} | [[Category:Life sciences}} | ||
Revision as of 13:00, 6 May 2007
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 Botulus microporus, a giant digenean parasite from the intestine of a lancetfish
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Aspidogastrea |
"Flukes" or "fatworms" is the common name applied to the flat, leaflet like endoparasites of class Trematoda within the phylum Platyhelminthes. This term can be traced back to the Saxon name for flounder, and refers to the flattened, rhomboidal shape of the worms.
All trematodes are parasitic flatworms. Previous classification systems included the Monogenea amongst the trematoda, alongside the Digenea and Aspidogastrea, on the basis that they were all vermiform parasites. The taxonomy of the Platyhelminthes is being subjected to extensive revision, thanks to modern phylogenetic studies; modern sources place the Monogenea in a separate class within the phylum. Moreover, there are no known cases of human infection with Aspidogastreans, therefore the use of the term "fluke" in relation to human beings refers solely to digeneans (require at least two hosts for the completion of their life cycle).
Types of Flukes
The flukes can be categorized into three groups on the basis of the systems they infect. Intestinal flukes occur attached to the mucosa of the intestine, some of the intestinal flukes infecting human beings are the species of genera Echinostoma Gastrodiscoides, Heterophyes, Metagonimus, etc. Some zoonotic flukes, e.g., Echinostoma ilocanum and Heterophyes heterophyes can infect human beings because of exposer, though their definitive hosts are other mammals like dog, cats, etc. Tissue flukes infect biological tissues of liver, lungs or bile duct attaching themselves on their surface. Some of the flukes of this category are lung fluke, e.g., Paragonimus westermani, and liver flukes, e.g., Clonorchis sinensis, Fasciola hepatica, Fasciolopsis buski, Dicrocoelium spp., etc. The third category of flukes is known as blood flukes, and inhabit the blood in some stages of their life cycle. Blood flukes include various species of the genus Schistosoma (Bilharzia), like S. japonicum, S. mansoni, S. haematobium, etc.
General Morphology
Flukes are laterally expanded to oval to oblong shape, and flattened dorso-ventrally into thin sheet. The unsegmented fluke body is covered by a tough cuticular tegument for its protection from digestive enzymes of the host. Anterior body end is produced into an oral cone for bearing an oral sucker with a centrally placed mouth. Posterior to this is a ventral sucker called acetabulum for strong attachment on the surface of the host organs. Alimentary canal is incomplete, as the intestine never open out via an anus. A small opening at the posterior end of the body is the common pore for protonephric excretory system. Most of the flukes are hermaphrodite having the organs of both sexes in a single individual. Although there is a common gonopore, cross fertilization is facilitated whenever possible. Species of Schistosoma differ from other fluke in two major aspects: They are dioecious with well-defined sexual dimorphism. Their body is elongated, female being more slender, cylindrical and permanently lodged in the gynaecophoric canal of male.
Life Cycles
Flukes being mostly digenetic, have a complex life cycle, often involving several intermediate hosts. Depending on the types of the parasite, the eggs pass from the host with the feces, sputum or the urine. When the eggs reach water, they hatch into free-swimming larvae called miracidia. The miracidia penetrate a specific fresh water snail or other molluscan intermediate host to become second larvae called sporocysts. The cells inside the sporocysts divide by mitosis to form redia larvae. Rediae, in turn, give rise to free-swimming larvae known as cercariae, which escape from the mollusk into water again. In general case, the cercaria larvae burrow through exposed skin using enzymes, penetrate another intermediate host (often an arthropod but can also be aquatic vegetation) and then encyst as metacercariae. When this host is eaten by the definitive host, the metacercariae excyst and develop into adult to repeat the life cycle. In case of Schistosoma, cercaria larvae infect definitive host (man) by directly penetrating the skin while in water. For more information on life cycles, see the respective pages on Digenea and Aspidogastrea.
Pathogenicity
Pathogenicity of the flukes varies with the sites of their infection. In the intestinal fluke, patient may show abdominal discomfort (diarrhea, nausea, vomiting, abdominal pain, ulceration) associated with the inflammation of the gut wall, as well as facial, abdominal and lower limb edema due to immune sensitization caused by the foreign proteins of the parasites. Among the tissue flukes, liver flukes cause liver abscesses, fibrosis, jaundice, and a type of hepatitis, while the Lung flukes produce symptoms similar to pulmonary tuberculosis. Infection of blood flukes causes fever and chills, but also elevates the number of white blood cells (eosinophils), as well as abdominal pain resulting from enlargements of the liver and spleen. Some parasitic trematodes chemically castrate their host.
Treatments
Medication is achieved generally by the use of different types of antimony containing drugs. They are effective against the flukes of all kinds.
Prophylaxis (preventive measures) includes personal hygiene, community sanitation, awareness campaign against toilet and sewage discharge in or near water resources, control of intermediate host, treatment of the infected persons and the pets, disinfection of contaminated water reservoirs, swimming pools, etc.
ReferencesISBN links support NWE through referral fees
- Gibson, D.I., Bray, R.A. & Jones, A., Keys to the Trematoda, 3 Volumes ISBN 0851995470
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[[Category:Life sciences}}
