Lesson on schistosomiasis (bilharziasis): Causes, Symptoms and Treatment. Schistosomiasis is caused by parasitic blood flukes from the genus schistosoma. Schistosoma cercariae penetrate human skin and enter the bloodstream of the infected individual, where the parasites enter the portal vein. Schistosoma parasites also enter the mesenteric and bladder circulations, where they release eggs. Symptoms of schistosomiasis are related to the location of the parasites, the parasite burden and the amount of eggs produced. Systems affected in schistosomiasis include the hepatic, splenic, genitourinary, pulmonary, and nervous systems.