Schistosoma
377559
219303968
2008-06-14T16:06:29Z
194.80.231.138
{{Taxobox
| name = ''Schistosoma''
| image = Schistosoma_mansoni.jpg
| image_width = 250px
| image_caption = ''Schistsoma mansoni'' egg
| regnum = [[Animal]]ia
| phylum = [[Platyhelminthes]]
| classis = [[Trematoda]]
| subclassis = [[Digenea]]
| ordo = [[Strigeidida]]
| familia = [[Schistosomatidae]]
| genus = '''''Schistosoma'''''
| genus_authority = Weinland, 1858
| subdivision_ranks = Species
| subdivision =
''[[S. mansoni]]''<br>
''[[S. japonicum]]''<br>
''[[S. mekongi]]''<br>
''[[S. intercalatum]]''<br>
''[[S. haematobium]]''<br>
''[[S. indicum]]''<br>
''[[S. nasale]]''<br>
''[[S. leiperi]]''<br>
''[[S. malayensis]]''<br>
''[[S. rodhaini]]''
}}
A genus of [[trematode]]s, '''''Schistosoma''''' spp., commonly known as '''blood-flukes''' and '''bilharzia''', cause the most significant infection of humans by [[flatworm]]s ([[schistosomiasis]]) and are considered by the [[World Health Organization]] as second in importance only to [[malaria]], with hundreds of millions infected worldwide. Adult worms parasitize [[circulatory system|mesenteric blood vessels]]. Eggs are passed through [[urine]] or [[feces]] to [[fresh water]], where larval stages can infect a new host by penetrating the skin.
==Taxonomy==
There are four species of schistosome which are infective to humans:
*'''''[[Schistosoma mansoni]]''''', found in [[Africa]], [[Brazil]], [[Venezuela]], [[Suriname]], the lesser [[Antilles]], [[Puerto Rico]], and the [[Dominican Republic]]. It is also known as ''Manson's blood fluke'' or ''swamp fever''. Freshwater snails of the ''[[Biomphalaria]]'' genus are an important host for this trematode.
*'''''[[S. japonicum]]''''' whose common name is simply ''blood fluke'' is found widely spread in [[Eastern Asia]] and the southwestern [[Pacific]] region. In [[Taiwan]] this species only affects animals, not humans. Freshwater snails of the ''[[Oncomelania]]'' genus are an important host for ''S. japonicum''.
*'''''[[S. mekongi]]''''' is related to ''S. japonicum'' and affects both superior and inferior mesenteric veins. ''S. mekongi'' differs in that it has smaller eggs, a different intermediate host, and longer prepatent period in the mammalian host.
*'''''[[S. haematobium]]''''', commonly referred to as the ''bladder fluke'', originally found in Africa, the [[Near East]], and the [[Mediterranean]] basin, was introduced into India during World War II. Freshwater snails of the ''[[Bulinus]]'' genus are an important host for this parasite.
''S. indicum'', ''S. nasale'', ''S. leiperi'' are all parasites of [[ruminant]]s.
==Morphology==
Adult schistosomes share all the fundamental features of the digenea. They have a basic [[symmetry (biology)#Bilateral symmetry|bilateral symmetry]], oral and ventral suckers, a body covering of a [[syncytium|syncytial]] [[integumentary system|tegument]], a blind-ending [[digestive system]] consisting of [[mouth]], [[oesophagus]] and bifurcated [[cecum|caeca]]; the area between the tegument and alimentary canal filled with a loose network of [[germ layer#Mesoderm|mesoderm]] [[Cell (biology)|cells]], and an excretory or osmoregulatory system based on [[flame cell]]s. Adult worms tend to be 10-20 mm long and use [[globin]]s from their hosts' [[hemoglobin]] for their own circulatory system.
==Reproduction==
Unlike other trematodes, the schistosomes are [[dioecious]] - i.e., the sexes are separate. The two sexes display a strong degree of [[sexual dimorphism]], and the male is considerably larger than the female. The male surrounds the female and encloses her within his ''gynacophoric canal'' for the entire adult lives of the worms, where they reproduce sexually.
==See also==
{{commonscat|Schistosoma}}
For a full discussion of [[biological life cycle|life cycles]], [[symptom]]s and control measures, see the main article on [[schistosomiasis]].
==External links==
*[http://www.dfid-kar-water.net/w5outputs/output_summary_sheets/control_schistosomiasis_os.html British Department for International Development Control of Schistosomiasis]
*[http://www.who.org The World Health Organisation]
*[http://www.path.cam.ac.uk/~schisto/ University of Cambridge Schistosome Laboratory]
[[Category:Platyhelminthes]]
[[Category:Parasites]]
[[ar:بلهارسيا]]
[[cs:Schistosoma]]
[[de:Pärchenegel]]
[[es:Schistosoma]]
[[fr:Schistosoma]]
[[pt:Schistosoma]]
[[fi:Halkiomadot]]
[[zh:血吸蟲]]