Transmission+-+Schistosomiasis

The vector for the parasite causing schistosomiasis is the freshwater snail (pictured below). This snail discharges the infectious form of the parasite, known as cercariae, into its freshwater dwellings, and thereby infects the human hosts through contact with the water.

http://www.cdc.gov/parasites/schistosomiasis/

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Below is a visual depiction of the life cycle of schistosomiasis:



1. The active parasite is released into the water in the excrement of a contaminated host 2. The parasite reproduces (eggs hatch and release miracidia (free swimming larvae) into the water) 3. Miracidia come in contact with the snail, and penetrate its tissue 4. The Miracidia develops within the tissue of the snail, advancing to the stage of 'Sporocyst'-- an encased sac containing reproductive cells 5. Cercariae, the infectious form of the parasite, is released by the snail into the water where it swims freely 6. The human host comes in contact with the contaminated water, and the cercariae penetrates the skin 7. During skin penetration the Cercariae loses its tail and becomes a schistome 8. The schistosomulae circulate in the blood stream and pervade the body 9. The parasites migrate with the blood to the liver where they mature 10. Adult parasitic worms pair off and migrate to the venules of the bowel and rectum, or to the venous plexus of the bladder (depending on the subtype) and release eggs into the blood stream and fecal matter 11. If the host defecates in the freshwater, eggs in the fecal matter can commence the cycle in another host

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