Schistosomiasis (bilharzia) is caused by a parasitic worm - schistosoma. It predominantly affects urinary and liver systems. It affects over 200 million people worldwide, and is said to be second to malaria in economic impact. 

Schistosoma japonicum, S hematobium, and S mansoni are the three most important species that infect humans. The schistosomes live in the bowel lumen and lay eggs in the mesenteric veins. The eggs may then embolize to the portal vein, where they cause an inflammatory reaction with a granulomatous response, eventual fibrosis, and presinusoidal hypertension. The eggs themselves do not survive and may subsequently calcify.

Chronic infection with either S japonicum or S mansoni result in the formation of cirrhosis and the risk of development of hepatocellular carcinoma. The diagnosis is based on epidemiologic data, clinical manifestations, eosinophilia, the presence of living eggs at stool examination, or positive serologic findings for Schistosoma infection. At histologic analysis, mild hepatic schistosomiasis is characterized by white, pinhead-sized granulomas scattered throughout the liver.