Medical science has found out that certain infections play a role in cancer in animals. More recently, infections with certain viruses, bacteria, and parasites have been recognized as risk factors for several types of cancer in humans. 

Worldwide, infections are linked to about 15% to 20% of cancers. This percentage is even higher in developing countries, but it is lower in the United States and other developed countries. This is partly because certain infections are more common in developing countries, and partly because some other risk factors for cancer, such as obesity, are more common in developed countries.

Infections can raise a person’s risk of cancer in different ways. For example:

  • Some viruses directly affect the genes inside cells that control their growth. These viruses can insert their own genes into the cell, causing the cell to grow out of control. 
  • Some infections can cause long-term inflammation in a part of the body. This can lead to changes in the affected cells and in nearby immune cells, which can eventually lead to cancer. 
  • Some types of infections can suppress a person’s immune system, which normally helps protect the body from some cancers.

Any of these changes might lead to a higher risk of cancer.

Even though the infections described here can raise a person’s risk of certain types of cancer, most people with these infections never develop cancer. The risk of developing cancer is also influenced by other factors. For example, infection with Helicobacter pylori (H pylori) bacteria might increase your risk of stomach cancer, but what you eat, whether or not you smoke, and other factors also affect your risk.

Many of the infections that influence cancer risk can be passed from person to person, but cancer itself cannot. A healthy person can’t “catch” cancer from someone who has it. 

Bacteria infections That Could Cause Cancer

Bacteria are very small living things that are made up of only one cell. Most bacteria are harmless, but others can cause illness. Some are even cancer-causing. 

Helicobacter pylori 

Stomach cancers one of the more common types of cancer worldwide. H pylori infections can cause stomach ulcers. It can damage the stomach’s inner lining. Some of these alterations could lead to stomach cancer over time. H pylori also has some association  to stomach lymphoma. 

Most patients with H pylori infection never get stomach cancer. H pylori may also lessen the chance of other types of cancer, however it’s unknown how. 

H pylori infects 2/3 of adults worldwide. Developing countries and older age groups have greater infection rates. It spreads in several ways. The fecal-oral pathway involves contaminated food or water. Mouth-to-mouth transmission is possible. 

Other causes can cause stomach cancer. Nitrites are found in cured foods, some water, and vegetables. Certain bacteria, such as H pylori, can transform them into stomach-cancer-causing chemicals. 

Antibiotics can treat H pylori infections. People with ulcers or a history of ulcers should be screened for H pylori and treated if infected. After early stomach cancer removal, H pylori testing and treatment is suggested. 

Chlamydia trachomatis

Chlamydia trachomatis is a common organism that can infect both men and women’s reproductive systems. It’s sexually transmitted. 

Most women have no symptoms from reproductive organ infections. This means women with chlamydia don’t realize they’re infected unless their pelvic samples are tested. It’s frequent in sexually active young women and can last years if not treated. 

Some studies have revealed that women with past or current chlamydia infections may be at higher risk for cervical cancer. 

Studies haven’t established that chlamydia causes cancer, but it may boost HPV proliferation. Women who had chlamydia and HPV are more likely to have HPV when retested than other women. More research are needed to validate these findings, but there are already compelling reasons to be screened for chlamydia and treated if it is identified. 

Long-term chlamydia infection can cause infertility in women by scarring the Fallopian tubes. Chlamydia can enhance the chance of HIV infection when exposed to an HIV-infected sexual partner, like other genital ulcer-causing illnesses.

Some Parasitic Infections That Could Cause Cancer.

Some parasitic worms that can live inside a person can also make it more likely that they will get some types of cancer. These organisms are not found in the United States, but they can be a problem for people who live or travel in other parts of the world. 

Opisthorchis viverrini and Clonorchis sinensis are types of flatworms that live in the liver. They have been linked to a higher risk of bile duct cancer. The liver and intestines are connected by tubes called bile ducts. These infections are caused by eating freshwater fish that is raw or not fully cooked. Most of them live in East Asia, and only a few live in other places. 

Schistosoma haematobium is a parasite that lives in the water of some Middle Eastern, African, and Asian countries. Schistosomiasis, which is caused by this parasite, has been linked to bladder cancer. Researchers are also looking into possible links to other types of cancer.