Infectious factors and cancer

Some infectious agents can actually cause cancer or increase the risk of cancer. Some viruses can disrupt the signals that control cell growth and proliferation. Infections can weaken the immune system, leaving the body less able to fight cancer. Some infectious agents cause chronic inflammation, which can lead to cancer. Of all the infectious agents, viruses are the most important for cancer development. Most of them are transmitted from person to person through blood and other body fluids, so it is possible to protect yourself by getting vaccinated, avoiding unprotected sex, and not sharing needles.

Epstein-Barr virus (EBV). This is a type of herpes virus that, in addition to the well-known mononucleosis, can also cause lymphoma and cancer of the epipharynx (upper part of the throat). It is mainly transmitted through saliva, for example by kissing and sharing toothbrushes or glasses. It can also be transmitted through blood, and the infection is lifelong. It is estimated that more than 90% of people will be infected with this virus during their lifetime, but most people do not have any symptoms. There is currently no vaccine or any specific treatment.

Hepatitis B and C viruses (HBV and HCV). These viruses can lead to chronic liver inflammation and ultimately liver cancer. Both viruses are transmitted through blood (blood transfusions, sharing needles), unprotected sex, or from mother to child during childbirth. In Croatia, mandatory vaccination against hepatitis B for healthcare workers was introduced in the 1990s, mandatory vaccination of children in the sixth grade of primary school was introduced in 1999, and universal vaccination in newborns in 2007. The vaccination is carried out in three doses, after which more than 95% of those vaccinated develop a protective antibody titer and such people are considered to be protected for life. Since the introduction of vaccination, there has been a significant decrease in the number of patients. There is currently no vaccine for hepatitis C, but with new therapies there is a possibility of curing the disease.

Human immunodeficiency virus (HIV). HIV is the virus that causes AIDS, a state of weakened immunity that is a breeding ground for the development of other infections that can lead to cancer. People infected with HIV have an increased risk of developing several types of tumors, such as Kaposi's sarcoma, lymphoma, cervical, anal, lung, liver, and throat cancer. HIV is transmitted through blood and unprotected sex, and the greatest risk is among homosexuals and intravenous drug users. There is no vaccine, but significant progress has been made in treating those infected.

Human papillomavirus (HPV). HPV is a virus that has many subtypes, and infection with high-risk subtypes is the cause of almost all malignant cervical tumors. It can also cause cancer of the oropharynx (middle part of the throat), vagina, vulva, and penis. High-risk types of HPCV are spread through direct sexual contact, including vaginal, oral, and anal sex. Several types of vaccines have been developed to prevent infection. Three types of vaccines against HPV infection are available in Croatia: bivalent, quadrivalent, and 9valent. All three vaccines protect against infection with types 16 and 18, which cause more than 70 percent of cervical cancers. The quadrivalent vaccine also contains types 6 and 11, which most often cause genital warts, while the nine-valent vaccine, in addition to types 16, 18, 6 and 11, also contains 31, 33, 45, 52, 58. It is recommended to get vaccinated before the start of sexual activity (before contact with the virus). However, vaccination is also recommended for those who are sexually active because people who are already infected are usually not infected with all the types against which the vaccine is given.

Image 1. Human papillomavirus is the most important factor in the development of cervical cancer. Today, infection with high-risk types can be successfully prevented by vaccination, which could largely eradicate this disease.

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1). It can cause an aggressive type of non-Hodgkin lymphoma called adult T-cell leukemia/lymphoma. The virus is spread through blood (sharing needles, transfusions), unprotected sex, or from mother to child during pregnancy or breastfeeding. Infection with this virus is uncommon in Croatia, and is most common in Japan and African countries. Most infected people do not get sick and do not have symptoms, but there is no vaccine or specific treatment.

Kaposi's sarcoma-associated herpesvirus, also called herpesvirus type 8, can cause Kaposi's sarcoma. Most infected people have no symptoms, but there is no vaccine or specific treatment.

Merkel Cell polyomavirus . This virus can lead to the development of Merkel cell carcinoma, a rare but very aggressive form of skin tumor. It is believed that most adults are infected with this virus through direct or indirect contact. The probability of developing the disease increases significantly in persons who are additionally infected with HIV. There is no specific treatment for the infection.

Helicobacter pylori. This is a bacterium that is a known cause of stomach ulcers and can lead to cancer or so-called MALT lymphoma of the stomach. It is believed to be transmitted through contaminated food or water and direct oral contact. According to some estimates, two-thirds of the world's population are carriers of this bacterium, and the infection rate is particularly high in less developed countries. Infection with H. pylori is successfully treated with antibiotics.

Opisthorchis viverrini. This parasite causes bile duct cancer and is primarily found in Southeast Asia. It is transmitted through raw or undercooked fish that contains larvae. The infection can be treated with antiparasitic drugs.

Schistosoma hematobium. This is a parasite found in Africa and the Middle East, lives in some types of snails, and can cause bladder cancer. It is transmitted through contact with contaminated fresh water containing larvae. It is treated with antiparasitic drugs.

Additional interesting facts

Globally, as many as 1 in 5 cancer cases worldwide are caused by infectious factors . This type of cancer is most common in less developed countries and areas, where personal hygiene is poor and conditions and lifestyles are conducive to the spread of infectious diseases. This primarily applies to Africa, Asia and South America, where viruses and other infectious factors are the cause of up to 31% (1 in 3) of all cancer cases.

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