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- Human papillomaviruses (HPVs) Human papillomaviruses (HPVs) are a group of more than 150 related viruses. They are called papillomaviruses because some of them cause papillomas, which are more commonly known as warts.
- Epstein-Barr virus (EBV) EBV is a type of herpes virus. It is probably best known for causing infectious mononucleosis, often called “mono” or the “kissing disease.”
- Hepatitis B virus (HBV) and hepatitis C virus (HCV) Both HBV and HCV cause viral hepatitis, a type of liver infection. Other viruses can also cause hepatitis (hepatitis A virus, for example), but only HBV and HCV can cause the long-term (chronic) infections that increase a person’s chance of liver cancer.
- Human immunodeficiency virus (HIV) HIV, the virus that causes acquired immune deficiency syndrome (AIDS), doesn’t appear to cause cancers directly. But HIV infection increases a person’s risk of getting several types of cancer, especially some linked to other viruses.
- Overview
- 1. Epstein-Barr virus (EBV)
- 2. Hepatitis B virus (HBV)
- 3. Hepatitis C virus (HCV)
- 4. Human immunodeficiency virus (HIV)
- 5. Human herpes virus 8 (HHV-8)
- 6. Human papillomavirus (HPV)
- 7. Human T-lymphotrophic virus (HTLV)
- 8. Merkel cell polyomavirus (MCV)
- How do viruses cause cancer?
Viruses are tiny, infectious microbes. They’re technically parasites because they require a host cell to reproduce. Upon entry, the virus uses components of the host cell to complete its life cycle.
Some viruses can cause or contribute to the development of cancer. These viruses are called oncogenic viruses.
Unlike other viruses, such as influenza viruses, that cause an acute infection, oncogenic viruses often cause long-term, persistent infections.
It’s estimated that viruses account for about 20 percent of cancers. And there may be more oncogenic viruses that experts aren’t aware of yet.
EBV is a type of herpes virus. You may be familiar with it as the cause of infectious mononucleosis, or mono.
EBV is most often spread through saliva. It can be contracted through coughing, sneezing, and close contact, such as kissing or sharing personal items.
The virus can also be spread through blood and semen. This means you can encounter it through sexual contact, blood transfusions, or organ transplants.
Most EBV infections occur during childhood, although not everyone who contracts the virus has symptoms. Once you’ve contracted it, it remains in your body for the rest of your life. But it eventually lies dormant in your body.
Mutations that occur in cells due to EBV infection may contribute to certain rare cancers, including:
•Burkitt’s lymphoma
HBV causes viral hepatitis. Hepatitis is an inflammation of the liver. Many people with HBV go on to recover following an acute infection. However, some develop a chronic (long-term) HBV infection.
The virus spreads through bodily fluids, including blood, semen, and vaginal secretions.
Common ways infection can occur include:
•having unprotected sexual activity with someone who has the virus
•sharing needles
•sharing personal items that could contain blood, including razors and toothbrushes
Like HBV, HCV also causes viral hepatitis.
According to the American Cancer Society, HCV is less likely than HBV to cause symptoms. But it’s more likely to cause a chronic infection. As a result, some people may have an HCV infection and not know it.
HCV spreads the same way HBV does. However, sexual activity seems to be a slightly less common cause of HCV transmission.
Similarly to HBV, a chronic HCV infection can lead to prolonged liver inflammation and damage, increasing a person’s risk of liver cancer.
HIV is a retrovirus that can lead to the development of AIDS.
HIV infects and destroys cells in the immune system called helper T cells. As the numbers of these cells decline, the immune system has a harder time fighting infections.
HIV spreads through bodily fluids, including blood, semen, and vaginal fluids.
Some ways that transmission can occur include:
•unprotected sexual activity with someone who has the virus
•sharing needles
You may sometimes see HHV-8 referred to as Kaposi sarcoma-associated herpes virus (KSHV). Like EBV, it’s a type of herpes virus.
Infection with HHV-8 is rare. It’s estimated that less than 10 percent of people in the United States develop an infection.
HHV-8 is mostly spread by saliva, although it can also be transmitted through sexual contact, organ transplants, and blood transfusions.
It causes a rare type of cancer called Kaposi sarcoma. This cancer affects the lining of blood vessels and lymph vessels. HHV-8 can be found in the cells of these tissues.
Normally, the immune system keeps the virus under control. As a result, most people with an infection don’t have any symptoms or develop Kaposi sarcoma.
However, people who have a weakened immune system, due to HIV for example, are at an increased risk for developing Kaposi sarcoma. This is because their immune system may not be able to keep the HHV-8 in check.
According to the National Cancer Institute, there are more than 200 types of HPV. Some types of cause warts to form on the skin, while others cause warts to form on the genitals, throat, or anus. However, HPV infection may not always cause symptoms.
Many types of HPV are spread through skin-to-skin contact during vaginal, anal, or oral sex. Because the virus can spread through skin contact, condom and dental dam use can lower, but not completely prevent, the chances of transmission.
Many people with an HPV infection eventually go on to clear it. However, in some cases long-term HPV infection can lead to cellular changes that can contribute to the development of several cancers, including those of the:
•cervix
•vagina
•vulva
Like HIV, HTLV is also a retrovirus. It’s more common outside of the United States in areas such as Japan, the Caribbean, Africa, the Middle East, and South America.
HTLV spreads through blood. Potential means of transmission include:
•unprotected sexual activity
•childbirth
•breastfeeding
•needling sharing
MCV is a recently discovered virus. Most people contract the virus during childhood and don’t have any symptoms.
It’s unclear how MCV is transmitted, thought experts think skin-to-skin contact is a likely culprit, along with coming into contact with contaminated objects or surfaces.
Oncogenic viruses can cause cancer through different mechanisms, which can include:
•alteration of cellular genes, either by mutation or by tampering with how genes are expressed
•suppressing or disrupting the immune system
•causing long-term inflammation
It’s important to remember that not all viral infections lead to cancer. There are several factors that can influence whether infection with an oncogenic virus will progress to cancer. These can include things like the health of your immune system, genetics, and environment.
Cancer is also a complex disease with many factors that can affect its development. This makes it tricky to say that a virus directly causes cancer. It’s more accurate to think of viruses as one contributing factor in the development of cancer.
Researchers know that there are several viruses that can lead to cancer. For example, the human papillomavirus (HPV) can cause cervical and several other cancers. And hepatitis C can lead to liver cancer and non-Hodgkin’s lymphoma. Studying viruses and cancer is helping researchers develop vaccines and other ways to reduce cancer risk.
- Kellie Bramlet Blackburn
Jan 25, 2019 · Human tumor viruses account for an estimated 12% to 20% of cancers worldwide. Viruses can lead to cancer by associating with host proteins, proliferating when the human immune system is weakened, and hijacking proliferating human cells.
There are several human viruses and bacteria currently known to be associated with cancer. A common theme indicates that these microorganisms have evolved mechanisms to hamper the pathways dedicated to maintaining the integrity of genetic information, preventing apoptosis of the damaged cells and causing unwanted cellular proliferation.
In 12% of cancers, seven different viruses have been causally linked to human oncogenesis: Epstein-Barr virus, hepatitis B virus, human papillomavirus, human T-cell lymphotropic virus, hepatitis C virus, Kaposi's sarcoma herpesvirus, and Merkel cell polyomavirus.
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Both benign and malignant tumors are classified according to the type of cell from which they arise. Most cancers fall into one of three main groups: carcinomas, sarcomas, and leukemias or lymphomas. Carcinomas, which include approximately 90% of human cancers, are malignancies of epithelial cells.
