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Viruses and bacteria

Few would connect viruses and bacteria to cancer, but some viruses and bacteria do cause cancer. It is estimated that viral and bacterial infections cause 15 to 20 % of all cancers in the world.

Cancers caused by infections are more common in developing countries than in developed countries.

Various viruses and bacterial infections cause cancer in different ways. Some directly affect genes that determine cell growth, others cause chronic inflammatory conditions that may ultimately lead to cancer. Some infections weaken the people’s immune system whereby the body cannot fight cancer.

“Depending on the virus and bacteria, you can protect your health in different ways.”

Most people who get a viral or bacterial infection do not get cancer. Many other factors, such as lifestyles, have an effect on cancer in addition to infection.

You can protect your health in various ways depending on the virus and bacteria. You can protect against certain viruses by using a vaccine or a condom. But there is not always a means of protection.


HPV (human papillomavirus) is a common virus that causes changes in cervical cells, for example. HPV virus is one of the most well known carcinogenic viruses.

Inflammation caused by papilloma virus is the most important risk factor in cervical cancer. Without viral infection, no cervical cancer can develop. Infection does not, however, always lead to cancer.

Up to 80 % of people are infected with HPV at some stage, but most of the viral infection disappears without causing changes.

HPV adheres directly to skin or mucous membranes, for example in the genital area. Such infections are most common among 20-25 year-olds.

What cancer does HPV cause?

There are over 100 known human papillomaviruses. Only some of these viruses can cause cancer. Viruses are divided into low-risk papillomaviruses that can cause benign changes (cutaneous warts, laryngeal papilloma, genital warts) and high cancer risk papillomaviruses.

Carcinogenic HPV damages cell DNA and causes cells to divide and grow uncontrollably. This can lead to cancer.

Carcinogenic papillomaviruses (HPV types 16 and 18) can cause cancer of the cervix. They can also cause a portion of cancers of the vulva, vagina, penis, anus, and head and neck area.

“A small proportion of cellular changes progress to cervical cancer precursors.”

High cancer risk HPV infection in the genital area is almost always symptom-free and recovers by itself. However, a small proportion of infections are prolonged. In women, prolonged infection can lead to cervical cell changes. A small proportion of cellular changes progress to cervical cancer precursors and eventually develops, without cure, into cervical cancer.

What can I do?

The risk factors for cervical cancer include people who started having sexual intercourse when young, having many sex partners, and smoking. Condoms do not provide full protection against infection, but they reduce the risk of infection. There is no treatment for HPV infection in itself.

The Pap cervical smear sample can be used to detect for changes to cells on the cervix. Women can also be given a test for HPV. The HPV test can determine whether women have a high risk of papilloma viral infection. If infection is detected, the Pap test can then be done to determine possible cell changes.

Cervical Cancer (All About Cancer website)

HPV vaccine

Having an HPV vaccination can prevent the human papillomavirus. The vaccine protects against the most common HPV types. It prevents cervical cancer precursors as well as HPV-induced vaginal and extracellular cancer precursors.

The vaccine provides the best protection when taken before sexual activity begins. The vaccine is effective only in people who have never had HPV infection.

HPV vaccine is currently part of the national vaccine programme. It is given to sixth grade girls.

Anyone under the age of 26 can also receive the vaccine.

Read more about the HPV vaccine:

HPV vaccine (THL)

Cervical cancer screening

One of the most important methods in cervical cancer prevention is regular Papa screening. Cervical cancer screening can prevent cervical cancer precursors from becoming cancerous. In Finland, all women of 30, 35, 40, 45, 50, 55 and 60 years of age are invited for screening. In some municipalities screening is also provided for people aged 25 and 65.

You should take part in cervical cancer screening even if you have had an HPV vaccine. The vaccine does not protect against all types of the virus and does not work against existing infections.

Cervical cancer screening

Hepatitis B (HBV) and Hepatitis C (HCV) are viruses that cause hepatitis. Hepatitis B and C are rare in Finland.

Hepatitis B infection is transmitted via unprotected sex and the blood, for example from used needles and syringes. The virus may also be transmitted from mother to child during childbirth or breastfeeding.

Read more about hepatitis B

Reliable information on hepatitis B and vaccine against it: (in Finnish)

Preventable diseases (in Finnish)

Hepatitis C is transmitted via the blood, for instance from used syringes and needles. Though rare, hepatitis C infection can be due to sexual contact or mother-to-child transmission in childbirth.  In Finland, hepatitis C virus infections are mainly among people who use intravenous drugs and who share syringes with other users.

Read more about hepatitis C:

Hepatitis C (THL)

Hepatitis B (THL)

What sort of cancer does hepatitis cause?

Hepatitis B infection and hepatitis C infection can lead to liver damage and sometimes to liver cirrhosis. Over the years, 10 to 20 % of patients with cirrhosis develop liver cancer develops.

What can I do?

There is a vaccine against hepatitis B. It is not generally included in the Finnish national vaccine programme because the virus is rare here. The vaccine can be obtained free of charge as part of a national vaccination programme, if a person belongs to a particular risk group, such as those suffering from haemorrhagic septicaemia.

There is no vaccine against hepatitis C. In Finland, the risk of hepatitis C infection is very low.

Condoms protect against sexually transmitted hepatitis infections. Clean syringes and needles prevent intravenous drug transmission. It is best not to get tattoos or piercings when you go abroad.

Hepatitis C (THL)

The infection caused by the Helicobacter pylori is one of the most common infections. Helicobacter lives in the gastric mucosa.

Nearly half of people in the world are infected with H. pylori. The infection caused by H. pylori is much more common in developing countries than in developed countries. It has been found to be associated with unhygienic conditions. H. pylori is more common in elderly people.

“Nearly half of people in the world are infected with H. pylori.”

Helicobacter causes chronic inflammation of stomach mucosa. The great majority of H. pylori does not cause serious symptoms. However, helicobacter can cause gastric and duodenal ulcers. Changes caused by Helicobacter in the stomach increase the risk of gastric cancer.

Read more about H. pylori:

Helikobakteeri (Terveyskirjasto)

The Epstein-Barr virus (EBV) is a herpes virus that causes inflammation of the throat of lymphoid tissue. EBV is best known for causing inflammatory mononucleosis..

EBV is a common virus that can be passed from one person to another by coughing, sneezing, or through food and drink. Most people carry EBV even though have no symptoms. EBV cannot  be got rid nor is there a vaccine against it.

“It is very rare for a herpes virus carrier to develop cancer.”

The herpes virus weakens the immune defense system that exposes cells to changes. EBV infection can cause Burkitt lymphoma, Hodgkin’s lymphoma, and certain cancers in the nose and throat area.

Another cancer associated with the herpes virus is the human herpes virus 8 (Kaposi’s Associated Herpes Virus, or KSHV). KSHV infections are very rare in Finland. This virus is transmitted by unprotected sex and via the blood. KSHV infection can cause Kaposi’s sarcoma.

It is very rare for the herpes virus carrier to develop cancer. For healthy people with a good immune defense system, herpes virus infections do not increase the risk of cancer.


HIV infection (hi virus) does not directly cause cancer. However, people with HIV are at greater risk of developing certain cancers because their immune defense system has deteriorated drastically.

Read more about HIV:

HIV (THL) (link)

Information about HIV (HIVpoint)