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).
Among protozoan parasites, Toxoplasma gondii, Cryptosporidium parvum, Trichomonas vaginalis and Theileria are associated with specific cancer cells.
Roundworms such as Strongyloides stercoralis, Heterakis gallinarum, and Trichuris muris are known to cause cancer in animals.
A Danish physician Johannes Fibiger discovered it in 1907, and experimentally showed that he could induce stomach cancer in rats using the roundworm infection in 1913.
Theodor Maximillian Bilharz, a German physician at the Kasr el-Aini Hospital in Cairo recovered the adult fluke from a dead soldier in 1851.
This creates the pathological lesions found in the bladder wall, ureter and renal; and also tumour, both benign and malignant.
Infection with the parasite, called opisthorchiasis is the major cause of cholangiocarcinoma, a cancer of the bile ducts, in northern Thailand, the Lao People's Democratic Republic, Vietnam and Cambodia.
[17] Generally opisthorchiasis due to O. viverrini is harmless without any clinical symptoms, but in rare cases, cholangitis, cholecystitis, and cholangiocarcinoma can develop.
[22] General clonorchiasis is indicated with fatigue, abdominal discomfort, anorexia, weight loss, diarrhea, liver cirrhosis and jaundice.
[23] Infection with malarial parasite Plasmodium falciparum is classified by IARC as probable (Group 2A) carcinogen.
There is a close association between the cat liver fluke Opisthorchis felineus and bile duct cancer among people in Russia.