The disease is caused by several species of fluke worms, each of which has an identical life cycle involving humans and fresh water snails. The parasite's eggs are found in the feces of infected humans. Once the feces reach water, the eggs hatch into free swimming worms which can burrow into the foot of a snail. The parasite uses the snail as a host to produce thousands of larvae. Those larvae are released back into the water, where they can burrow through the skin of humans that swim in the water. From there, the larvae move to the lungs and then to the liver. The fluke lives there off of red blood cells and produces thousands of eggs which are released into the bloodstream where they are small enough to pass though the wall of the intestines to be excreted in feces to start the life-cycl