Carcinogenic parasite is a parasitic organism which depends on other organisms (called hosts) for their survival, and cause cancer in such hosts. Medically-proven carcinogenic parasites are three species of flukes (trematodes), namely the urinary blood fluke (Schistosoma haematobium), the Southeast Asian liver fluke (Opisthorchis viverrini) and the Chinese liver fluke (Clonorchis sinensis). S. haematobium is prevalent in Africa and the Middle East, and is the leading cause of bladder cancer (only next to tobacco smoking). O. viverrini and C. sinensis are both found in eastern and southeastern Asia, and are responsible for cholangiocarcinoma (cancer of the bile ducts). The International Agency for Research on Cancer declared them in 2009 as a Group 1 biological carcinogens in humans.