ONCOGENIC VIRUSES A REVIEW

JERRY EJE ABU

UJ/2010/NS/0755

AIM OF REVIEWThis study aims at highlighting the distribution and Epidemiology of Viruses Associated with Cancer.

OBJECTIVE OF THE REVIEW1. To highlight cancer causing viruses in human.2. To highlight the mechanisms they use to cause cancer.3. To highlight the epidemiology and distribution of these cancer causing viruses.

INTRODUCTIONViruses are only able to reproduce by entering a living cell and manipulating the

cell’s machinery to create more viruses. During the viral replication process, certain

virus’s DNA or RNA affect the host cell’s genes in ways that may cause it to become

cancerous. These viruses are known as oncogenic viruses, meaning viruses that

cause or give rise to tumors. Oncogenic viruses belong to a number of viral

families, including the RNA virus families Retroviridae and Flaviviridae and the DNA

virus families Hepadnaviridae, Herpesviridae, Poliomaviridae and Papillomaviridae

(Klein, 2002).

Some of the viruses now known or suspected of being linked to cancer in humans

include; human papilloma viruses, the Epstein-Barr virus, the hepatitis B and C

viruses, the human herpes virus 8, human immunodeficiency virus (HIV) and the

human T-lymphotrophic virus-1 (Liao, 2006).

BODY OF REVIEW

Table 1: Carcinogenic mechanisms of oncogenic viruses

Source: (International Agency for Research on Cancer, 2009)

When an oncogene is activated by mutation, the structure of the encoded protein is changed in a way that enhances its transforming activity. Many types of mutation occur in oncogenes (Rodenhuis, 1992).

GROUPS OF ONCOGENIC VIRUSES

Oncogenic viruses can be divided into 2 groups, based on their genetic

material, as DNA and RNA tumor viruses (Zheng, 2010).

Table 2: Human oncogenic RNA viruses.

Source: (Zheng, 2010) HTLV: Human T-cell leukemia virus.

Table 3: Human oncogenic DNA viruses.

Source: (Butel, 2000; Zheng, 2010; McLaughlin-Drubin and Munger, 2008; Zheng and Ou, 2009) HBV: Hepatitis B virus, EBV: Epstein-Barr virus, KSHV: Kaposi’s sarcoma-associated herpesvirus, HHV: Human herpes virus, HPV: Human papillomavirus, MCV: Molluscum contagiosum virus

Epidemiology of viruses associated with human cancerThe International Agency for Research on Cancer has comprehensively assessed

the carcinogenicity of the biological agents to humans based on epidemiological

and mechanistic evidence (IARC 2009). Seven viruses including Epstein–Barr

Virus (EBV), hepatitis B virus (HBV), hepatitis C virus (HCV), Kaposi’s sarcoma

herpes virus (KSHV), human immune deficiency virus, type-1 (HIV-1), human T

Cell lymphotrophic virus, type-1 (HTLV-1),and several types of human papilloma

virus (HPV) have been classified as Group1 human carcinogen.

PREVALENCE OF ONCOGENIC VIRUS INFECTION IN THE WORLD

HBV

HCV

HIV

PREVALENCE OF ONCOGENIC VIRUS INFECTION IN THE WORLD…..continue

HPV

HTLV-1

KSHV

INCIDENCE OF SOME VIRUS-CAUSED CANCERS IN THE WORLD

NASOPHARYNGEAL CARCINOMA

BURKITT LYMPHOMA

INCIDENCE OF SOME VIRUS-CAUSED CANCERS IN THE WORLD

HEPATOCELLULAR CARCINOMA

CERVICAL CANCER

KAPOSI’S SARCOMA

CONCLUSIONGlobally, viral infections contribute to about 15% to 20% of all human cancers (Zur, 2001). Several

viruses with oncogenic potential stimulate cell proliferation and cause tumors and cancer in

animals and humans. They act with different mechanisms depending on different host factors. The

tumor viruses with small genomes integrate into host cell chromosomal DNA and cause mutations

and chromosomal rearrangements that predispose to cancer (Murat, 2012). Viral infection is now

considered as the second major preventable cancer risk factor after tobacco use. The universal

immunization program against HBV in Taiwan and Gambia has successfully lowered the incidence

of Hepatocellular carcinoma (HCC) in the vaccinated population. The first HPV vaccine approved in

2006 are expected to reduce deaths from cervical cancer by 75%, a number that should be a great

inspiration for similar research on other human oncogenic viruses as well (Zheng and Ou, 2009).

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