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Schistosoma, blood fluke

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Taxonomic lineage

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Acoelomata - Platyhelminthes - Trematoda - Digenea - Strigeidida - Schistosomatoidea - Schistosomatidae - Schistosoma

General information

[shis"-, skis" to-so-miə'-sis], from the Greek - skhistos (split) and soma (body)
Originally thought a single organism with a split body, the parasite was eventually recognized as having male and female forms.
Schistosomiasis, which leads to chronic hepatic and intestinal fibrosis of the urinary tract, Swas first identified in Egypt in 1851 by German pathologist Theodor Bilharz and is also called bilharzia.

Schistosoma species are causative agents of a tropical disease schistosomiasis or bilharzia. Approximately 160 million persons throughout the world are infected, particularly in Africa, the Middle East, South America, and Southeast Asia by three main species: S. mansoni, S. japonicum, and S. haematobium.

Of the ~2700 genera of Digenean parasites, the 13 that comprise the Schistosomatidae are different in the following ways:

• they have two rather than three hosts
• they are dioecious (having female and male reproductive organs in separate individuals)
• they infect their hosts by directly penetrating the body surface, rather than being eaten
• they are intravascular parasites (live inside blood vessels)

No routine laboratory techniques were developed so far for culturing schistosomes through their complete life cycle in vitro as well as for expressing transgenes for targeted gene silencing and other purposes. Also, there are no schistosome cell lines. Therefore, analysis of schistosome-host interactions are very challenging and is confined mostly to traditional parasitological techniques.

Pathologies

• Acute pathology
  • Cercarial dermatitis, skin rash that can be accomanied by lesions and can persist for days, occurs upon massive penetration of skin by cercariae.
  • Katayama fever is a systemic hypersensitivity reaction against the migrating schistosomulae. The disease (fever, fatigue, myalgia, etc.) starts suddenly in a few weeks or even months after a primary infection. Most patients recover spontaneously after 2-10 weeks. This type of illness is not common in individuals who live in areas that are endemic for schistosomiasis. It occurs instead in those people who have no previous history of exposure.
• Chronic pathology
  • Urinary schistosomiasis (S. haematobium)
  • Intestinal schistosomiasis
  • Hepatic schistosomiasis and hepatosplenic schistosomiasis (S. mansoni, S. japonicum)
  • Ectopic ("displaced") schistosomiasis
    • Genital schistosomiasis (S. mansoni, S. haematobium)
    • Pulmonary schistosomiasis (S. mansoni)
    • Neuroschistosomiasis (S. japonicum, S. haematobium)

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References

• Gryseels B. et al. Human schistosomiasis. Lancet. 2006 Sep 23;368(9541):1106-18.
• Pearce EJ, MacDonald AS. The immunobiology of schistosomiasis. Nat Rev Immunol. 2002 Jul
• Etymologia: schistosomiasis Emerg Infect Dis. 2007 October; 13(10): 1476.
• Lewis FA et al. The NIH-NIAID schistosomiasis resource center. PLoS Negl Trop Dis. 2008 Jul 30;2(7):e267.
  

  The Three Species of Intermediate Hosts That Are Provided from The Schistosomiasis Center.
  From left, Bulinus truncatus truncatus (host for S. haematobium), Biomphalaria glabrata (host for S. mansoni), and Oncomelania hupensis hupensis (intermediate host for the Chinese isolate of S. japonicum; other subspecies of O. hupensis are also available).
  For size comparisons, the B. glabrata shown is approximately 5 mm in shell diameter.

• Major topic "Schistosoma" (free full-text articles in PubMed)
• Animal Diversity Web: Schistosoma mansoni.
• eMedicine: Schistosomiasis, Bladder