How Does a Virus Cause Cancer?
A virus is nothing more than DNA or RNA wrapped in a protein coat. What makes them unique is that they do not contain the necessary materials to function on their own. They are forced to invade a host cell (can be plant, animal, or bacterial) in order to thrive and reproduce.
There are several ways that a virus can cause cancer.
Viruses Known to Cause Cancer
Cancer viruses can be either DNA or RNA viruses. Viruses known to cause cancer are listed below, though it’s likely that others will be found in the future. Note as well ,that there are also some bacteria and parasites that are linked with the development of cancer.
Human Papillomavirus (HPV) and Cancer
The human papillomavirus (HPV) is a sexually transmitted virus affecting over 20 million Americans. It is the most common type of sexually transmitted infection. There are currently over one hundred known strains of HPV, but only around 30 of these are thought to cause cancer.
The strains of HPV most commonly associated with cancer include HPV 16 and HPV 18.
Vaccination for HPV – a shot that protects against HPV 16 and HPV 18 – is available for children between the ages of 11 and 12, and can be given starting at age 9 and as old as age 26.
Cancer currently associated with HPV infections include:
In some other cancers, the data is less certain. For example, HPV is linked to lung cancer, but it’s not known if HPV contributes to the development of lung cancer, if instead, having lung cancer increases the chance of contracting HPV, or if it is just a random occurrence and they are unrelated.
Thankfully, it appears that some of the cancers have a better prognosis when related to HPV infections. For example, throat cancers that are thought to be caused by a combination of smoking and alcohol have a much poorer prognosis than those felt to be caused by HPV.
Hepatitis B and Cancer
Infection with Hepatitis B virus (HBV) increases the risk of developing liver cancer.
These viral infections are extremely contagious are spread through the transmission of blood, semen, and other bodily fluids from one person to another. Common means of exposure include unprotected sex, mother to infant transmission during childbirth, and the sharing of intravenous needles (most often by drug use, but can also occur during tattooing).
Most people recover from an acute hepatitis B infection (roughly 70% have symptoms and the other 30% are asymptomatic), but some people go on to develop a chronic infection with hepatitis B, most commonly those who contract the disease in early childhood and those who do not have any symptoms. Liver cancer occurs much more commonly among those with chronic hepatitis B (hepatitis B carriers.)
Most children born since the 1980’s have been immunized against hepatitis B, and adults who have not been immunized should consider doing so.
Hepatitis C and Cancer
Hepatitis C infection also increases the risk of developing liver cancer. Until the 1980’s, hepatitis C infection (HCV) was known as non-A non-B hepatitis. The initial infection may have symptoms, but a significant number of people do not have symptoms. Unlike hepatitis B, in which the disease does not often become chronic, around 80% of people with hepatitis C develop a chronic infection.
As the immune system continues to attack the virus over time, fibrosis develops, eventually leading to cirrhosis. This chronic inflammation can also lead to liver cancer.
The virus is spread through infected blood, such as with transfusions and IV drug abuse, but many people do not have obvious risk factors for the disease. It is now recommended that adults born between 1945 and 1965 be tested for the disease, as well as others who may be at risk.
Epstein-Barr Virus (EBV) and Cancer
The Epstein-Barr virus is most commonly recognized for causing mononucleosis but is also linked with the development of several different types of lymphoma.
These include
Human Immunodeficiency Virus (HIV) and Cancer
HIV and cancer are linked in a few ways. Just as we’ve known for years that immunosuppressive drugs can weaken the immune system resulting in cancers, the immunosuppression caused by the HIV virus can predispose people with the disease to cancer. Non-Hodgkin lymphoma, Hodgkin lymphoma, primary CNS lymphoma, leukemia, and myeloma are all linked with the infection.
As noted above, it appears that HIV weakens the immune system (as does malaria) allowing the Epstein Barr virus to cause the transformation needed for lympohocytes to become a lymphoma. In addition to lymphomas, HIV increases the risk of Kaposi’s sarcoma, cervical cancer, lung cancer, anal cancer, and liver cancer.
T-Lymphotrophic Virus (HTLV-1) and Cancer
HTLV-1 is a retrovirus (similar to HIV) that causes adult human T-cell leukemia/lymphoma.
Human Herpes Virus 8 (HHV-8) and Cancer
HHV-8 can cause Kaposi’s sarcoma and is also known as KSHV – Kaposi sarcoma herpes virus.
Merkel Cell Polyomavirus
Merkel cell polyomavirus – known as McPyV – can cause a form of skin cancer known as Merkel cell carcinoma. Yet even though the virus is very common in the population as a whole, the cancer caused by it is uncommon.
Prevention of Cancer Caused by Viruses
An ounce of prevention is worth a pound of cure, and it’s notable that many of these viruses that can lead to cancer are passed from person to person. Practicing safe sex and not sharing needles are one way to lower risk. The importance of being healthy in general – eating right and exercising – is reinforced in seeing how suppressed immune function can raise the risk of some of the viral-induced cancers.
Overview of Viruses Linked to Cancer
Article Source: https://www.verywell.com/viruses-and-cancer-513624
Article Source References:
- Centers for Disease Control and Prevention. The Link Between HPV and Cancer.
- Centers for Disease Control and Prevention. Testing Recommendations for Hepatitis C Infection.
- Geng, L., and X. Wang. Epstein-Barr Virus-associated lymphoproliferative disorders: experimental and clinical developments. International Journal of Clinical and Experimental Medicine. 2015. 8(9):14656-71.
- Grundhoff, A., and N. Fischer. Merkel cell polyomavirus, a highly prevalent virus with tumorigenic potential. Current Opinion in Virology. 2015. 14:129-37.
- National Cancer Institute. Infectious Agents.
- Vedham, V., Verma, M., and S. Mahabir. Early-life exposures to infectious agents and later cancer development. Cancer Medicine. 2015. 4912):1908-22
