Viruses that cause cancer

Two million. That's how many cases of cancer are caused each year by... viruses. And which could therefore be avoided by limiting the spread of these infectious agents. Samuel Alizon and Ignacio Bravo, researchers at the Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (Mivegec) laboratory, explain.

What causes cancer? If we spontaneously think of tobacco, diet, sunlight, alcohol or genetic inheritance, we often forget a formidable cause: viruses. Silent carcinogens from which it is nevertheless often possible to protect oneself.

The link between viral infections and cancer was established as early as the 19th century. " In the 1840s, an Italian doctor noticed that cervical cancer, which was very prevalent among prostitutes, was almost non-existent among nuns," explains Ignacio Bravo. A distribution similar to that of sexually transmitted infections, which suggests that this cancer is linked to an infectious agent...

Papillomavirus

It wasn't until 1973 that a German virologist, Harald zur Hausen, identified the virus responsible for cervical cancer: the papillomavirus. Papillomaviruses, in fact," explains Samuel Alizon, " because some twenty strains of human papillomavirus, or HPV, have since been identified as responsible for the development of cervical cancer.

These viruses are transmitted during sexual intercourse and are widespread. It's estimated that over 80% of adults will be infected with oncogenic human papillomaviruses during their sexual lives," explains the specialist. More than 90% of these infections will be harmless, but unfortunately some will cause cancer. Thousands of new cases of cervical cancer are diagnosed every year, including 3,000 in France.

1 cancer in 10

Papillomaviruses, which are responsible for 100% of cervical cancers, can also cause cancers of the anus, vulva, vagina and throat. And they're not the only ones likely to cause cancer: the Espstein-Barr virus, responsible for mononucleosis, leads to the development of lymphoma in 1 in 10,000 cases. Hepatitis B and C viruses can cause liver cancer. In total, oncoviruses are responsible for one in ten cancers worldwide," explains Samuel Alizon. Given their enormous prevalence, they represent a major public health challenge".

To shed new light on these viruses, Samuel Alizon and Ignacio Bravo are coordinating multi-disciplinary work by international collaborators to better understand cancers of infectious origin. " These are the cancers we are most likely to be able to prevent, since we can use conventional methods of controlling infectious diseases, such as vaccination and screening," say the researchers.

A public health issue

The HPV vaccine has been available in France since 2006. " There are three vaccines that protect against the HPV16 and HPV18 viruses, which are the most oncogenic," say the researchers. Authorities currently recommend that young girls be vaccinated before their first sexual encounter. " Despite these recommendations, vaccination coverage remains very low in France: only 20% of teenage girls are vaccinated," explains Samuel Alizon, who deplores the fact that young boys are not also vaccinated: "On the one hand, papillomaviruses can also cause cancer and condyloma in men, and on the other, men can be carriers of the virus without being ill, and transmit it to their partners during sexual intercourse.

A real public health challenge, but also a research challenge. If vaccination coverage were to increase considerably, the prevalence of HPV16 and 18, which are targeted by the vaccine, would fall sharply, and could even be eradicated. " The vaccination context is exerting new selection pressure on HPVs, and the entire papillomavirus ecosystem is being impacted, without the possible consequences of these upheavals being known," explain the specialists. "It is therefore essential to continue to learn more about these viruses, so as to always be one step ahead.