الشيستوما
الشيستوما Schistosoma تنتشر هذه الطفيليات بصورة رئيسية في افريقيا حيث يبلغ عدد الاصابات المرضية حوالى 100 مليون اصابة كما تنتشر في بعض الدول مثل (مصر وسوريا تركيا وايران)
Schistosoma is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed schistosomiasis, which is considered by the World Health Organization to be the second-most socioeconomically devastating parasitic disease (after malaria), infecting millions worldwide.[1][2]
Adult flatworms parasitize blood capillaries of either the mesenteries or plexus of the bladder, depending on the infecting species. They are unique among trematodes and any other flatworms in that they are dioecious with distinct sexual dimorphism between male and female. Thousands of eggs are released and reach either the bladder or the intestine (according to the infecting species), and these are then excreted in urine or feces to fresh water. Larvae must then pass through an intermediate snail host before the next larval stage of the parasite emerges that can infect a new mammalian host by penetrating the skin.
التطور
The origins of this genus remain unclear. For many years it was believed that this genus had an African origin, but DNA sequencing suggests that the species (S. edwardiense and S. hippopotami) that infect the hippo (Hippopotamus amphibius) could be basal. Since hippos were present in both Africa and Asia during the Cenozoic era, the genus might have originated as parasites of hippos.[3] The original hosts for the South East Asian species were probably rodents.[4]
Cladogram
A cladogram based on 18S ribosomal RNA, 28S ribosomal RNA, and partial cytochrome c oxidase subunit I (COI) genes shows phylogenic relations of species in the genus Schistosoma:[5]
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Comparison of eggs
Geographical distribution
Geographical areas associated with schistosomiasis by the World Health Organization as of January 2017 include in alphabetical order: Africa, Brazil, Cambodia, the Caribbean, China, Corsica, Indonesia, Laos, the Middle East, the Philippines, Suriname, and Venezuela.[6] There had been no cases in Europe since 1965, until an outbreak occurred on Corsica.[7]
Schistosomiasis
The parasitic flatworms of Schistosoma cause a group of chronic infections called schistosomiasis known also as bilharziasis.[8] An anti-schistosome drug is a schistosomicide.
Species infecting humans
Parasitism of humans by Schistosoma appears to have evolved on at least three occasions in both Asia and Africa.
- S. guineensis, a recently described species, is found in West Africa. Known snail intermediate hosts include Bulinus forskalii.
- 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 genus Bulinus are an important intermediate host for this parasite. Among final hosts humans are most important. Other final hosts are rarely baboons and monkeys.[9]
- S. intercalatum. The usual final hosts are humans. Other animals can be infected experimentally.[9]
- S. japonicum, whose common name is simply blood fluke, is widespread in East Asia and the southwestern Pacific region. Freshwater snails of the genus Oncomelania are an important intermediate host for S. japonicum. Final hosts are humans and other mammals including cats, dogs, goats, horses, pigs, rats and water buffalo.[9]
- S. malayensis This species appears to be a rare infection in humans and is considered to be a zoonosis [citation needed]. The natural vertebrate host is Müller's giant Sunda rat (Sundamys muelleri). The snail hosts are Robertsiella species (R. gismanni, R. kaporensis and R. silvicola (see Attwood et al. 2005 Journal of Molluscan Studies Volume 71, Issue 4 pp. 379–391).
- S. 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 genus Biomphalaria are an important intermediate host for this trematode. Among final hosts humans are most important. Other final hosts are baboons, rodents and raccoons.[9]
- S. mekongi is related to S. japonicum and affects both the superior and inferior mesenteric veins. S. mekongi differs in that it has smaller eggs, a different intermediate host (Neotricula aperta) and longer prepatent period in the mammalian host. Final hosts are humans and dogs.[9] The snail Tricula aperta can also be experimentally infected with this species.[citation needed]
| Scientific Name | First Intermediate Host | Endemic Area |
|---|---|---|
| Schistosoma guineensis | Bulinus forskalii | West Africa |
| Schistosoma intercalatum | Bulinus spp | Africa |
| Schistosoma haematobium | Bulinus spp. | Africa, Middle East |
| Schistosoma japonicum | Oncomelania spp. | China, East Asia, Philippines |
| Schistosoma malayensis | Robertsiella spp. | Southeast Asia |
| Schistosoma mansoni | Biomphalaria spp. | Africa, South America, Caribbean, Middle East |
| Schistosoma mekongi | Neotricula aperta | Southeast Asia |
Species infecting other animals
Schistosoma indicum, Schistosoma nasale, Schistosoma spindale, Schistosoma leiperi are all parasites of ruminants.[citation needed]
Schistosoma edwardiense and Schistosoma hippopotami are parasites of the hippo.[citation needed]
Schistosoma ovuncatum and Schistosoma sinensium are parasites of rodents.[citation needed]
Morphology
Adult schistosomes share all the fundamental features of the digenea. They have a basic bilateral symmetry, oral and ventral suckers, a body covering of a syncytial tegument, a blind-ending digestive system consisting of mouth, esophagus and bifurcated caeca; the area between the tegument and alimentary canal filled with a loose network of mesoderm cells, and an excretory or osmoregulatory system based on flame cells. Adult worms tend to be 10–20 mm (0.39–0.79 in) long and use globins from their hosts' hemoglobin for their own circulatory system.
Reproduction
الصفات الشكلية
الجسم اسطوانى طول الذكر (10 - 15 ملم) بينما الأنثى (9_20 ملم)
جسم الذكر مسطح له حواف ملتفة للوسط مكونة القناة التناسلة او قناة الاحتضان تغطى الاشواك الصفيرة لحافة جسم الذكرالظهرية كما يحتوى الجسم على ممصين (فمى وبطنى)من اجل تثبيت الدودة بجدران الاوعية الدموية من الداخل يتميز بيض هذه العائلة بانه به اشواك في نهايته او جانبي البيضة ويوجد داخل الاوعية الدموية الصغيرة ويخرج مع البول او البراز.
أطوار الحياة
- المراسيديوم
- اسبوروسيست أول
- اسبوروسيست ثاني
- السركاريا(الطور المعدي)
أنواع الشيستسوما
- البلهاسيا البقرية
- شيستسوما جابونيكم
- شيستسوما مانسوى
- شيستسوما هيماتوبيوم
Treatment
Praziquantel is the current drug of choice against schistosomiasis. It is effective against all schistosome species that infect humans.[10][11] Oxamniquine is effective against Schistosoma mansoni infections, but relatively ineffective against Schistosoma haematobium and Schistosoma japonicum.[10]
References
- ^ "Schistosomiasis Fact Sheet". World Health Organization. Retrieved 10 August 2011.
- ^ "Schistosomiasis". Centers for Disease Control and Prevention. Retrieved 10 August 2011.
- ^ Morgan JA, DeJong RJ, Kazibwe F, Mkoji GM, Loker ES (August 2003). "A newly-identified lineage of Schistosoma". International Journal for Parasitology. 33 (9): 977–85. doi:10.1016/S0020-7519(03)00132-2. PMID 12906881.
- ^ Attwood SW, Fatih FA, Upatham ES (March 2008). "DNA-sequence variation among Schistosoma mekongi populations and related taxa; phylogeography and the current distribution of Asian schistosomiasis". PLOS Neglected Tropical Diseases. 2 (3) e200. Bibcode:2008PNTDi...2..200A. doi:10.1371/journal.pntd.0000200. PMC 2265426. PMID 18350111.
- ^ Brant SV, Morgan JA, Mkoji GM, Snyder SD, Rajapakse RP, Loker ES (February 2006). "An approach to revealing blood fluke life cycles, taxonomy, and diversity: provision of key reference data including DNA sequence from single life cycle stages". The Journal of Parasitology. 92 (1): 77–88. doi:10.1645/GE-3515.1. PMC 2519025. PMID 16629320.
- ^ WHO factsheet
- ^ خطأ استشهاد: وسم
<ref>غير صحيح؛ لا نص تم توفيره للمراجع المسماةlancet - ^ Britannica Concise Encyclopedia 2007
- ^ أ ب ت ث ج Manson-Bahr PE, Bell DR, eds. (1987). Manson's Tropical Diseases. London: Bailliere Tindall. ISBN 978-0-7020-1187-0.
- ^ أ ب Greenberg, Robert M.; Doenhoff, Michael J. (2017), "Chemotherapy and Drug Resistance in Schistosomiasis and Other Trematode and Cestode Infections", in Mayers, Douglas L.; Sobel, Jack D.; Ouellette, Marc et al. (in en), Antimicrobial Drug Resistance, Cham: Springer International Publishing, pp. 705–734, doi:, ISBN 978-3-319-46716-0
- ^ "Parasites - Schistosomiasis". Centers for Disease Control and Prevention. U.S. Department of Health & Human Services. 28 October 2020.
Further reading
- Ross AG, Sleigh AC, Li Y, Davis GM, Williams GM, Jiang Z, et al. (April 2001). "Schistosomiasis in the People's Republic of China: prospects and challenges for the 21st century". Clinical Microbiology Reviews. 14 (2): 270–95. Bibcode:2001CliMR..14..270R. doi:10.1128/CMR.14.2.270-295.2001. PMC 88974. PMID 11292639.