Scrotum of a male patient with testicular schistosomiasis. Schistosomiasis is caused by infection with small parasitic worms, known as flukes (Schistosoma sp.), that are found in freshwater. Initial infection is usually asymptomatic, but may cause itching. Later symptoms are dependent on the location of the worm's eggs within the body. Here it is causing an accumulation of fluid (hydrocele) in the testicles.