Viruses are responsible for only about 5% of human cancer. But they are much more common causes of cancer in animals, where their experimental study has played a key role in the identification of oncogenes. Both DNA and RNA viruses are implicated. * Hepatitis B virus (HBV) causes primary liver cancer. Vaccination of the children of susceptible populations is used for prevention.
* The Epstein Barr Virus (EBV) is implicated in nasopharyngeal cancer.
* The Human Papilloma Virus (HPV), especially certain subtypes like 16, are associated with cervical cancer. These viruses also cause warts, which are benign tumors. Some parasitic infections are associated with cancer.
* Infections with Schistosoma haematobium (schistosomiasis) may be associated with bladder cancer. This parasite enters the skin from water infected by snails.
* The liver fluke, Clonorchis sinensis, is associated with cancer of the gall bladder and hepatobiliary ducts.
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