infectious diseases
Schistosomiasis
Pathophysiology of Schistosomiasis
AdultSchistosomaworms live and copulate within venules of the mesentery (typicallyS. mekongi,S. intercalatum,S. japonicumandS. mansoni) or bladder (typicallyS. haematobium). Some eggs penetrate the intestinal or bladder mucosa and are passed in stool or urine; other eggs remain within the host organ or are transported through the portal system to the liver and occasionally to other sites (eg, lungs, central nervous system, spinal cord). Excreted eggs hatch in freshwater, releasing miracidia (first larval stage), which enter snails. After multiplication, thousands of free-swimming, forked-tailed cercariae are released. Cercariae penetrate human skin within a few minutes after exposure. When they penetrate the skin, they lose their forked tail and transform into schistosomula, which travel through the bloodstream to the liver, where they mature into adults. The adults then migrate to their ultimate home in the intestinal veins or the venous plexus of the genitourinary tract. Eggs appear in stool or urine 1 to 3 months after cercarial penetration. Estimates of the adult worm life span range from 3 to 7 years. The females range in size from 7 to 20 mm; males are slightly smaller. 