Carcinogenic parasites are parasitic organisms that depend on other organisms (called hosts) for their survival, and cause cancer in such hosts.
The first true carcinogenic parasite discovered was Schistosoma haematobium.
A British Surgeon Reginald Harrison, at the Liverpool Royal Infirmary, was the first to note its role in cancer. In 1889, he found that four people out of five cancer victims had bilharzia.
S. haematobium is a digenetictrematode found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans. It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is the leading cause of bladder cancer (only next to tobacco smoking).
O. viverrini is a food-borne liver fluke that mainly attacks the area of the bile duct. Infection with the parasite, called opisthorchiasis is the major cause of cholangiocarcinoma, a cancer of the bile ducts.
The evolution of parasites with humans has enabled them to envisage effective strategies for their long-term survival in hosts. Such long-term existence of these pathogens is often precarious to the human body. The chronic inflammation and immunomodulation caused by these pathogens also induces oxidative stress at the site of infection. Chronic inflammation is significantly recognized for cancer initiation and development. If pathogenic infection is untreated, such prolonged inflammation and increased oxidative stress can cause cancer.
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