Parasitic worms are spread through contact with contaminated food and water. They can also be transmitted from animals and insects to humans. Not all parasitic worms infect the digestive tract. Unlike other Schistosoma flatworm species that infect the intestines and cause intestinal schistosomiasis, Schistosoma haematobium species infect the bladder and urogenital tissue. Schistosoma worms are called blood flukes because they inhabit blood vessels . After the females lay their eggs, some eggs exit the body in urine or feces. Others may become lodged in body organs ( liver , spleen , lungs ) causing blood loss, colon obstruction, enlarged spleen, or excessive fluid buildup in the abdomen. Schistosoma species are transmitted by contact with water that has been contaminated with Schistosoma larvae. These worms enter the body by penetrating the skin .