Viruses as a Cause of Cancer

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Table of Contents

Introduction
Epstein-Barr Virus (EBV)
Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV)
Human Herpes Virus 8
Simian Virus 40(SV40)
Human T-Lymphotropic Virus-1 (HTLV-I)
HIV (Human Immunodeficiency Virus)
References

Introduction

Viruses and cancer are linked. These are very small organisms which most are not seen from an ordinary microscope. The protein coat surrounds their genetic form of DNA or RNA. Viruses are reproduced by entering a living cell where they multiply to make more viruses, this means that they cannot reproduce on their own but do by entering the host’s living cells. There they reproduce; this is done by inserting their own RNA or DNA into the host’s cell machinery. This insertion of the virus into the host’s cell may alter the host’s genome which may become cancerous. Cell fusion in a human being is a process of bone and muscle formation. Viral infection in some instances causes cell fusion in human tissue, although this is harmless because they are believed to die without causing harm to the host. However, cell fusion triggered by viruses, according to a recent study shows that virus plays a role in the development of human cancer. Viruses are used as a vector for human gene therapy. These fusogenic viruses as vectors might cause cancer. The use of fusogenic viruses as vectors for gene therapy or other clinical applications should be looked into consideration to avoid the development of cancer.

It has also been established that the AIDS virus may directly cause cancer of the immune system. This is done by switching on a dormant cancer gene when it enters the cell’s DNA of the host. HIV the virus which causes AIDS suppresses the immune system. Thus people with AIDS have higher chances of getting this cancer. Research has shown that retroviruses can cause cancer in birds by inserting themselves near a dormant cancer gene. The same sort of thing could also happen to a human being. Viruses are spread from one person to another in different ways:

Oral, Vaginal, or Anal sex with an HIV- HBV Infected person without any protection, Needle injection or any equipment used on an HIV, HBV Infected person, during birth (careless handling of infants from mothers with HIV or breastfeeding by mothers with HIV, HBV,) and lastly Blood products, example in blood transfusion containing HIV or organ transplant from an HIV infected person.

The virus can help to cause some cancer by causing genetic changes; several viruses have been researched and have shown their possibility of causing cancer in human beings. These viruses are Human papillomaviruses (HPVS), Epstein-Barr virus (EBV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human Immunodeficiency Virus, Human Herpesvirus 8 (HHV-8), Human T- lymphotropic virus-1 (HTLV-1), Feline leukemia virus (FELV) and Simian Virus 40(SV40).

HPV causes cervical cancer and warts on the genital organs, skin, mouth, and larynx. They are a group of over a hundred related viruses, infected through touch, for example, through sex thus it spreads easily in people who are sexually active. HPV is treated by removing or destroying infected cells although it disappears after some time without treatment.

HPV in women causes cervical cancer. This is the most common cancer in women worldwide. In developed countries like the United States, it’s rare because of use of Pap test which detects pre-cancerous changes in cervix cells caused by HPV then, which can be treated faster thus preventing any development to cervical cancer, unlike in developing countries which most women have developed this cancer due to lack of these Papst or lack of earlier treatment. It has been shown through studies that most women with HPV will not develop into cervical cancer while nearly all women with cervical cancer show HPV positive.

Looking at the other side, HPV also plays a role in developing cancer of the vulva, vagina, penis, anus, mouth, throat, head, and neck. Some practices like smoking and drinking increase the risk of developing cancer as they work together with this virus. Vaccines have been developed for this cancer, for instance, Gardasil is approved for protecting females at the age of nine to twenty-six in cervical cancer.

Epstein-Barr virus (EBV)

These viruses are spread through kissing, coughing, sneezing, and sharing drinking or eating utensils. It is a herpes virus and causes mononucleosis. In the first few weeks, the infected person doesn’t show any symptoms. EBV enters into B-cells (type of white blood cells) and stays there. This increases the risk of one getting nasopharyngeal cancer, Burkitt lymphoma, Hodgkin’s disease, or even stomach cancer. This cancer is mostly seen in developing countries like Africa and parts of Southern Asia.

Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV)

HBV and HCV can cause chronic infection of viral hepatitis. This increases the risk of one getting liver cancer. This cancer is higher in developing countries compared to developed countries. HBV and HCV are spread through sharing of needles, unprotected sex, during birth with an infected mother, etc. HBV causes symptoms like yellowing of the eye and skin, flu-like although many people improve or recover completely from this infection some develop into chronic conditions which increases the risk of developing liver cancer.

Most people with HCV are more likely to develop chronic infections leading to liver damage or even cancer. HCV has no symptoms as that of HBV thus many people are not aware of these infections.

Human Herpes Virus 8

It’s also called Kaposi Sarcoma-associated herpes virus. (KS HV) Kaposi Sarcoma (KS) is a rare, slow-grading cancer. It is found underneath the skin which appears as reddish-purple or blue-brown tumors. Cancer is common in people with HIV infections because of the reduced immune system. The study has not yet shown how HHV-8 causes the Kaposi Sarcoma virus. The infection of this virus is immune suppressed, in blood cancer individuals, for example, primary effusion lymphoma increases higher chances of Kaposi Sarcoma. The virus has also been found in people with multi-centric castle man disease, the disease with an overgrowth of the lymph nodes that acts very much like lymphoma. This case study shows that cancer develops mostly in immune-suppressed individuals like people with HIV and organ transplants. HHV-8 is related to other viruses as the one which causes cold sores, genital herpes, Epstein-Barr virus (EBW), Cytomegalovirus although those other viruses do not cause Kaposi Sarcoma.

Feline Leukemia Virus (FeLV), virus is associated with feline leukemia. This is a fatal disease found in domestic cats, especially in America. It has not been established if it can be passed to the human being through infection. A vaccine has been developed to protect cats against feline leukemia.

Simian Virus 40(SV40)

Mesothelioma is a rare cancer. It is found in the lining of the lungs or abdomen. Simon virus 40 is a virus mostly found in monkeys and those is possible according to the research that it can infect a human being and cause mesothelioma. The virus is also found to cause some brain cancers, bone cancers, and lymphomas. According to the studies, specimens were found to contain SV40 on the cells of some cancers, fragments, or DNA although the same issues are found on non-cancerous cells or tissue fragments. Also, it was noted that infection of lab animals with these viruses causes mesotheliomas. This was done on mouse cells and hamsters.

More research has been done and has shown that there is no high risk of one getting mesothelioma or other cancers after receiving vaccines contaminated with SV40. It has also been noted that many older people aged between fifty and above, especially in men have mesothelioma though they have not been exposed to this SV40-contaminated vaccine. More research is being done to give accurate results.

Human T-Lymphotropic virus-1 (HTLV-I)

This virus causes tropical spastic paraparesis (TSP) which is a degenerative nerve disease. It has also been shown to cause adult T-cell leukemia (ATL). The virus is a retrovirus and uses RNA in genetic code. During reproduction, they have an extra step by using the reverse transcriptase enzyme. A human cell infected by these viruses acquires the virus DNA genes and becomes part of the chromosome, this can alter the gene, causing genetic mutation hence there will be abnormal cell division which often leads to cancer. The virus is spread through blood transfusion from an infected person, unprotected sex from an HIV-infected person, injection needles, during childbirth, and breastfeeding from an infected mother.

HIV (Human Immunodeficiency Virus)

HIV is transmitted from one person to another through intimate contact with vaginal secretions, breast milk, semen, and blood from an infected person. This is passed through organ transplant from infected person, unprotected sex with HIV infected person, during birth and breastfeeding by mothers with HIV, and Blood products containing HIV during blood transfusion.

After this transmission, HIV infects helper T cells destroying them thus suppressing the immune system of the body. Thus HIV causes acquired immune deficiency syndrome (AIDS). The weakening of the immune system increases the chances of a person getting other several types of cancer especially cancer caused by HHV-8 and HPV. The immune system also helps to fight and kill newly formed cancer cells, the weakening of the immune system will therefore increase high risk of one getting cancer. Kaposi Saroma, invasive cervical cancer, non–Hodgkin lymphoma, central nervous system lymphoma are among the cancers found in HIV-infected persons. These statistics show that HIV-infected person have higher risk of acquiring the viral cancer than a healthy person. Therefore a weak immune system mostly allows new cancer to survive long enough to begin forming tumors.

Other cancers found in HIV-infected persons are invasive anal cancer, Hodgkin disease, lung cancer, cancer of the mouth and throat, skin cancer, and cancer of the testicles.The risks of these cancers can be reduced by using anti-HIV drugs especially those with Kaposi Sarcoma and several cancers.

In conclusion, we have seen that cancers and viruses are linked i.e. Viruses can help to cause some cancer by causing genetic changes. Cervical cancer and genital warts is linked to HPV Hepatitis B virus causes primary liver cancer. EBV infects most people. People with repeated attacks of malaria plus this virus have high risk of Burkitt lymphoma that affects children, especially in sub–Saharan Africa. EBV infection in UK causes Hodgkin’s disease. EBV can cause lymphoma in AIDS patients and transplant patients.

References

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Davi, P. and Ellen C. Jennifer A. (2006). The language of medicine, Elsevier Australia, Page 629.

James, R. (2000). Biology problem solver, research and education association pp.103- 187.

Lauren, S. (2004). How cancer works, New York, Jones and Bartlett Publisher, pp. 136-158.

Paul G Gwendolyn R (2007), Barton’s microbiology for the health sciences, New York, Lippincott Williams and Wilkins, pp. 53- 89.

Philip C. Harnis, P. (2001), Fundamental of cancer Epidemiology. New York, Prentice Hall, Page 120 -204.

Sharyl, J. (2003). Large scale biomedical science, London, National Academic Press pp. 83-99.

Sylvia N (1999). Hidden Arguments, Political Ideology and Disease Prevention Policy, London, Rutgers University Press science, pp. 18-63.

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