How Can a Virus Cause Cancer?

Viral particles (blue) kill a cell (yellow) as they come bursting out to spread infection.
Viral particles (blue) kill a cell (yellow) as they come bursting out to spread infection.

We often hear about viruses, but what are viruses exactly? Viruses are extremely small particles that cannot be seen by the naked eye or even a typical microscope. They consist of DNA wrapped in a protein coat. Interestingly, since viruses are not able to reproduce on their own, viruses are not truly alive like bacteria or our cells.

How do viruses work?

They must infect host cells (such as humans or animals) and hijack the cell’s machinery to multiply. Once a virus enters into a cell, the cell cannot tell its own DNA apart from the viral DNA, so the virus’s DNA is copied and its genes are expressed. To speed up the production of new viral particles, often these viral genes make cells grow faster. Some viruses insert themselves into our own DNA so that every time a cell divides, it carries the virus with it. Viruses cause infection and replicate in many different ways. The diseases and symptoms that viruses cause are a byproduct of their ultimate goal, and that is to replicate themselves and spread, just like anything else in the world that evolves. But what you may not know is that some viruses can lead to a horrible side effect – cancer.

Viruses cause cancer? How???

Several different types of viruses can cause cancer, includingbut one example that has been a very hot topic in the media lately is human papillomavirus, or HPV. You may recognize HPV as a sexually transmitted disease – as it causes warts and is typically spread during sex. Most of these viral infections can be treated, and symptoms eventually pass. However, this virus contains genes that cause cells to grow very quickly and inactivate its defenses against mutations. In some people, these genes are enough to make cells become cancerous. HPV is the most common cause of cervical cancer, and is responsible for over 70% of all cases. HPV infections can also cause cancer in the penis, anus, vagina and even the throat. Fortunately, there is good news! There are vaccines that have been created against HPV, which is a simple way to prevent these types of cancers.

Hepatitis C is another virus that can cause cancer, but for different reasons. Hepatitis C is spread by blood or sexual contact and infects the liver. It causes massive amounts of damage and death to liver cells and leads to scarring in the liver. Since it is very difficult for your body to fight off a hepatitis C infection, the battle with this disease lasts for many years or a lifetime; it is a chronic infection. This puts a lot of strain upon your body to heal and repair damaged tissue over and over and over again. Each time your cells divide to heal this damage, there is a small chance that a random mutation can happen. If these mutations accumulate, it can cause normal cells to become cancerous. In this case, it can lead to liver cancer.

What can I do?

The most important message to remember is that although most people infected with these viruses will not get cancer, it is good practice to minimize the risk of getting infected in the first place, and to always get vaccinated if a vaccination is available!

This article was written by Mike Pryszlak. Mike is currently completing the second year of his PhD at the University of Toronto. He studies how normal stem cell genes are changed in cancer stem cells. To learn more about Mike and his research check out our members page.

References and further reading:

http://www.cancer.org/cancer/cancercauses/othercarcinogens/infectiousagents/infectiousagentsandcancer/infectious-agents-and-cancer-viruses

http://www.cdc.gov/hpv/cancer.html

Liao, John B. Viruses and Human Cancer. 2006. Yale J Biol Med. 79:115-122.

Oliveria Andrade, L. J., A. D’Oliveira et. al. Association Between Hepatitis C and Hepatocellular Carcinoma. 2009. J Glob Infect Dis. 1:33-37.

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