Certain infectious agents, including viruses, bacteria, and parasites, can cause cancer in infected people or increase the risk that cancer will form. Some viruses can disrupt normal controls on cell growth and proliferation. They may also increase the chance that a person will be affected by other cancer risk factors, such as UV radiation or substances in tobacco smoke that cause cancer. Some viruses, bacteria, and parasites also cause chronic inflammation, which may lead to cancer.
Most of the viruses that are linked to an increased risk of cancer can be passed from one person to another through blood and/or other body fluids. You can lower your risk of infection by getting vaccinated, not having unprotected sex, and not sharing needles.
Human Papillomaviruses (HPVs)
Infection with high-risk types of HPV cause nearly all cervical cancers. They also cause most anal cancers and many, oropharyngeal, vaginal, vulvar, and penile cancers. In the United States, experts recommend that children ages 11 and 12 receive a vaccine that prevents infection with the types of HPV that cause most HPV-associated cancers. Children as young as age 9 and adults as old as 26 can also be vaccinated. HPV infections in the cervix can be found with specific tests. Although HPV infections themselves cannot be treated, the cervical cell changes these infections can cause over time can be treated. For more information, see the HPV and Cancer, Human Papillomavirus (HPV) Vaccines, and Pap and HPV Testing fact sheets.
Hepatitis B Virus and Hepatitis C Virus (HBV and HCV)
Chronic infections with HBV or HCV can cause liver cancer. Since the 1980s, infants in the United States and most other countries have been routinely vaccinated against HBV infection. If you are an adult who has not been vaccinated against HBV and have an increased risk of HBV infection, experts recommend that you get vaccinated as soon as possible. Vaccination is especially important for healthcare workers and other professionals who come into contact with human blood. The U.S. Centers for Disease Control and Prevention (CDC) also recommends that everyone in the United States born from 1945 through 1965 be tested for HCV, along with other populations at increased risk for HCV infection. If you think you may be at risk for HBV or HCV infection, ask your doctor about being tested. These infections do not always cause symptoms, but tests can show whether you have the virus. If so, your doctor may suggest treatment. Also, your doctor can tell you how to keep from infecting other people.
Human T-cell Leukemia/Lymphoma Virus Type 1 (HTLV-1)
HTLV-1 can cause a type of leukemia and lymphoma.
Human Immunodeficiency Virus (HIV)
HIV is the virus that causes AIDS. Infection with HIV weakens the immune system and makes the body less able to fight off other infectious agents that cause cancer. People infected with HIV have an increased risk of Kaposi sarcoma, lymphoma, and cancers of the cervix, liver, lung, and anus. HIV infection does not always cause symptoms. If you think you may be at risk for HIV, ask your doctor about being tested. If you test positive, your doctor may suggest treatment and can tell you how to keep from infecting other people. For more information, see the HIV Infection and Cancer Risk fact sheet.
Epstein-Barr Virus (EBV)
Infection with EBV, a type of herpes virus, has been linked to an increased risk of lymphoma and cancers of the stomach and nasopharynx.
Human Herpesvirus 8 (HHV8)
HHV8, also known as Kaposi sarcoma-associated herpes virus (KSHV), can cause Kaposi sarcoma.
Merkel Cell Polyomavirus (MCPyV)
MCPyV can cause Merkel cell carcinoma, which is a rare type of skin cancer.
Helicobacter pylori (H. pylori)
H. pylori is a type of bacteria that can cause stomach cancer and a type of lymphoma in the stomach lining. It can also cause stomach ulcers. If you have stomach problems, see a doctor. Infection with H. pylori can be found and treated. For more information, see the Helicobacter pylori and Cancer fact sheet.
This flatworm (fluke), which is found in Africa and the Middle East, can cause bladder cancer.
This flatworm (fluke), which is found in Southeast Asia, can cause cholangiocarcinoma (cancer of the bile ducts in the liver).