Bilharzia is transmitted when an infected person urinates or defecates in or near a water source and passes the eggs of the parasite into the water. The eggs hatch and become small parasitic worms, which grow into snails. The fully grown parasites then pass out of the snails and swim freely in fresh water. When these parasites come into contact with a person, they enter the skin and grow inside the blood vessels, producing eggs that cause bilharzia.
Attribution: Straight Talk Foundation