Figure 8.

Life cycle of Schistosomes. Unlike other Trematodes, schistosome adults have two sexes and are located in blood vessels. Eggs from human hosts hatch into free swimming miracidia which infect specific snail species. These develop into two generations of sporocysts and result in the production of cercariae which are released from the snail and swim freely in water where they encounter and penetrate the skin of the human host. The cercariae shed their tails to become schistosomules, which enter small veins and develop into adult worms in mesenteric veins. Their exact location varies with species. S. hematobium occurs in the bladder venous plexus and rectal veins. Eggs are deposited in the small veins of the portal and perivesical systems. In S. mansoni (pink arrows) and S. japonicum (green arrows) the eggs migrate to the lumen of the intestine and are excreted in the feces. In S. hematobium (black arrows) eggs migrate towards the lumen of the intestine or the bladder and uterus and are eliminated with feces or urine.