Infectious causes of cancer

Estimates place the worldwide risk of cancers from infectious causes at 16.1%. Viral infections are risk factors for cervical cancer, 80% of liver cancers, and 15–20% of the other cancers. This proportion varies in different regions of the world from a high of 32.7% in Sub-Saharan Africa to 3.3% in Australia and New Zealand.Viruses are the usual infectious agents that cause cancer but Mycobacterium, some other bacteria and parasites also have an effect.

A virus that can cause cancer is called an oncovirus. These include human papillomavirus (cervical carcinoma), Epstein-Barr virus (B-cell lymphoproliferative disease and nasopharyngeal carcinoma), Kaposi's sarcoma herpesvirus (Kaposi's Sarcoma and primary effusion lymphomas), hepatitis B and hepatitis C viruses (), and Human T-cell leukemia virus-1 (T-cell leukemias). Bacterial infection may also increase the risk of cancer, as seen in Helicobacter pylori-induced gastric carcinoma. Parasitic infections strongly associated with cancer include Schistosoma haematobium (squamous cell carcinoma of the bladder) and the liver flukes, Opisthorchis viverrini and Clonorchis sinensis (cholangiocarcinoma).

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