Infectious Agents - pg.2

Human immunodeficiency virus (HIV)

HIV is a virus that causes acquired immune deficiency syndrome (AIDS). This virus does not appear to cause cancers directly, although an individual with an HIV infection has an increased risk of getting several types of cancer, especially some linked to other viruses such as HHV-8 (see section below) and HPV.

HIV is acquired through contact with blood, vaginal secretions, breast milk, or semen from an HIV-infected person.

Human immunodeficiency Virus Infection and Cancer

HIV infection has been linked to a higher risk of developing AIDS-associated malignancies; Kaposi sarcoma, cervical cancer, anal cancer, head and neck cancers certain types of lymphoma, primary effusion lymphoma, non-Hodgkin lymphoma and central nervous system lymphoma. Some non-AIDS associated malignancies such as lung, liver and some forms of skin cancer are rising as the HIV positive population ages

		Image Rendering of HIV - CISN Archives

Kaposi's sarcoma-associated Herpes Virus (KSHV) or Human herpes virus 8 (HHV-8)

KSHV/HHV-8 occurs in nearly all tumors in patients diagnosed with Kaposi sarcoma (KS). KS is a rare, slow-growing cancer first described in the 1870s by Dr. Moritz Kaposi in elderly men who lived in Mediterranean regions of southern Europe, the Middle East or the African continent. Early in the 1980's, at the beginning of the AIDS epidemic, it began to appear in predominantly young men with AIDS. Currently in resource rich countries the number of diagnosed cases of KS has dropped probably due to highly active antiretroviral therapy (HAART) for the treatment of HIV infection.

KSHV/HHV-8 is also related to other herpes viruses, such as the viruses that cause cold sores and genital herpes, Epstein-Barr virus (EBV), and cytomegalovirus (CMV). All herpes virus infections lie dormant in the body and never go away, even when there are no signs of disease. KSHV/HHV-8 appears to be spread by several means including sexual. Data show less than 10% of the US population is infected with this virus and it does not appear to cause disease in most healthy people.

Human T-lymphotrophic virus-1 (HTLV-1)

HTLV-1 is a human RNA retrovirus that causes T-cell leukemia and adult T-cell lymphoma (ATL) ATL is usually a highly aggressive non-Hodgkin's lymphoma. This cancer is found mostly in southern Japan, the Caribbean, Central Africa, parts of South America, and in some immigrant groups in the southeastern United States where its incidence seems to be growing.

		Image is of a scanning electron micrograph of HTLV-I virus (green) infecting a human Tlymphocyte (yellow). Infection with this virus can stimulate the T-cells to proliferate at an increased rate, causing a risk of developing leukemia.
Image courtesy of Dr. Dennis Kunkel/Phototake www.Britannica.com

Transmission of HTLV-1 may occur from mother to child through mother's milk, through sexual contact, or exposure to contaminated blood, either through blood transfusions or sharing of contaminated needles.

Bacteria

Helicobacter pylori (H. pylori)

The discovery of Helicobacter pylori (H. pylori) bacteria in most duodenal ulcers has revolutionized medical management of this chronic disease. In most cases, ulcers can be cured following appropriate antibiotic therapy, although the emergence of H. 8 pylori strains that are resistant to antibiotics is making treatment of these infections more difficult.

H. pylori are also considered a carcinogen (cancer-causing agent) because of its association with gastric (stomach) cancer; however, the factors which cause certain persons with H. pylori to develop gastric cancer are unclear. Data show that more than half of all cases of stomach cancer may be linked to H. pylori infection but most people who have these bacteria in their stomachs never develop cancer.

		Helicobacter pylori bacillus attacking the gastric mucosa.
Image provided by CISN archives. All rights reserved.

Chlamydia trachomatis

Although some studies imply that women whose blood test results show past or current chlamydia infection are at greater risk for cervical cancer than are women with a negative blood test, it has not been shown that chlamydia by itself can cause cancer. Chlamydia may work with HPV in some way that promotes cancer growth.

Chlamydia trachomatis is a relatively common kind of bacteria that can infect the female reproductive system and is spread by sexual contact. Typically women have no symptoms and do not know they are infected. This problem can be solved if samples taken when they have a Pap test also test for chlamydia. Chlamydia is very common in younger women who are sexually active, and may persist for years unless it is detected and treated. Men can also be infected with this bacteria but its role in cancer development is not well established.

Parasites

While parasitic worms are not found in the United States, they can be a concern for people who live in or travel to other parts of the world. Some parasitic worms that can live inside the human body may also raise the risk of an individual developing some kinds of cancer.

CISN Summary

Molecular techniques for identifying pathogens associated with cancer continue to be developed. Identifying a causal infectious agent can help in understanding the biology of these cancers, which can hopefully be translated into further development of antiviral and antimicrobial drugs and vaccines for their treatment and prevention.

In the last two decades several strategies against cancer-associated infectious agents have been developed. These included antibiotic therapy against H. pylori and two prophylactic vaccines against HBV and HPV.