schistosomiasis (LIFE CYCLE)

Schistosoma eggs are eliminated with feces or urine, depending on species  . Under appropriate conditions the eggs hatch and release miracidia  , which swim and penetrate specific snail intermediate hosts  . The stages in the snail include two generations of sporocysts  and the production of cercariae  . Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host  , and shed their forked tails, becoming schistosomulae  . The schistosomulae migrate via venous circulation to lungs, then to the heart, and then develop in the liver, exiting the liver via the portal vein system when mature,   . Male and female adult worms copulate and reside in the mesenteric venules, the location of which varies by species (with some exceptions)  . For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine  , and S. mansoni occurs more often in the inferior mesenteric veins draining the large intestine  . However, both species can occupy either location and are capable of moving between sites. S. intercalatum and S. guineensis also inhabit the inferior mesenteric plexus but lower in the bowel than S. mansoni. S. haematobium most often inhabitsin the vesicular and pelvic venous plexus of the bladder  , but it can also be found in the rectal venules. The females (size ranges from 7-28 mm, depending on species) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni,S. japonicum, S. mekongi, S. intercalatum/guineensis) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively  .