•Viruses are only able to reproduce by entering a living cell and manipulating the cell’s genes to create more viruses. During the viral replication process, certain DNA or RNA viruses affects the host cell’s genome in ways that may lead to cancer.
•An oncogenic virus is virus which could cause cancer. it’s refers to any virus with a DNA or RNA genome that reason most cancers and it’s also known as “tumor virus” or “cancer virus”. most of human and animal viruses do not motive cancer, likely because of longstanding co-evolution between the virus and its host.
•it is vital to observe that the process from the preliminary viral infection to tumor formation is gradual and inefficient; only a small percentage of viral infections development to cancer years after the preliminary infection. other elements may increase the threat of cancer including immune system complications, cell mutations, exposure to cancer agents and hereditary susceptibility.
•Tumor viruses come in a spread of types: Viruses with a DNA genome, along with adenovirus, and viruses with an RNA genome, just like the Hepatitis C virus (HCV), as can retroviruses having each DNA and RNA genomes (Human T- lmphotropic virus and hepatitis B virus, which typically replicates as a mixed double and single-stranded DNA virus but also has a retroviral replication aspect). in a lots of cases, tumor viruses do no longer cause cancer in their native hosts, but in dead-end species.
facts about virus lifecycle:
For maximum virus: (replication -> lysis -> progeny Virion)
lytic existence Cycle:
genome -> all viral proteins
latent life Cycle:
viral cell -> mobile -> integration (typically) -> transformation.
– some virus unique protein expressed (early function)
– sometimes latency may be additionally terminated. Cell should be infected by complete virus.
1/lack of growth manipulate
5/potential to form tumors
-viral genes intervene with manage of cell replication and other elements of the cellular phenotype
-transformed cells regularly exhibit chromosomal aberrations
-each DNA and RNA tumor virus can remodel cells .
-Integration of viral genome into the host chromosomes happens (usually)
DNA Tumor viruses:
1)Human papilloma virus
2)Kaposi’s sarcoma related Herpes Virus
3)Epstein-Barr virus (EBV)
4)Merkel cell polyoma virus (polyoma virus )
5)Human cytomegalo virus (related to mucoepidermoid carcinoma )
1-Human papilloma virus
There are over 100 unique varieties of human a viruses which can purpose warts on the pores and skin, mouth, genital organs and larynx. they may be spread via human direct contact and are a commonplace sexually transmitted ailment. presently there aren’t any powerful remedies for HPV other than the removal or destruction of infected cells. over the years, the immune system usually controls and destroys the virus.
Specific human papilloma viruses are recognized to cause cervical cancers, that is the second most commonplace cancer amongst women international.
HPV is anticipated to be the cause of 5% of cancers international in step with the national most cancers Institute. An oral HPV infection may purpose cancers of the oropharynx.
most cervical vulvar and penile cancers are related to kinds 16 and 18 (70% of penile most cancers )
powerful vaccine : quadrivalent recombinant HPV6.11.sixteen.18 proteins made in yeast – Gardasil – Cervarix
2) Kaposi’s sarcoma related Herpes Virus
Kaposi’s sarcoma-related herpesvirus (KSHV) or human herpesvirus 8 (HHV-eight) is present in all clinical variations of Kaposi’s sarcoma (that is a cancer commonly taking place in AIDS sufferers) and lymphoproliferative sicknesses: number one effusion lymphoma and multi-centric Castleman’s disease (MCD). research have proved the link among KSHV/HHV-8 contamination and growth of Kaposi’s sarcoma. The virus encodes a number of genes homologous to human genes concerned in cell proliferation, anti-apoptosis, angiogenesis and cytokine action. In Kaposi’s sarcoma and primary effusion lymphoma, most tumor cells show proof of latent contamination, with a limited gene expression pattern.
3)Epstein-Barr virus (EBV)
it’s far one of 8 acknowledged human herpesvirus sorts within the herpes family, and is one of the most common viruses in humans. it’s far known as human herpesvirus four (HHV-4). it’s thee best known to be the reason of infectious mononucleosis (glandular fever). it’s also related to particular sorts of cancer, along with Hodgkin’s lymphoma, Burkitt’s lymphoma, gastric cancers, nasopharyngeal carcinoma. there’s proof that infection with EBV is associated with a higher chance of certain autoimmune illnesses, especially dermatomyositis, systemic lupus erythematosus, rheumatoid arthritis, Sjögren’s syndrome, and multiple sclerosis. 20000 most cancers cases each year are a result of EBV. infection with EBV occurs by using the oral switch of saliva and genital secretions. The virus stays with the person at some stage in existence by way of infecting epithelial cells and a kind of WBC called B cells. but, after a few weeks of preliminary infection, most people display no signs and symptoms.
4)Merkel cell polyomavirus (polyomavirus )
Polyomaviruses are small, non-enveloped DNA viruses, which might be massive in nature. In immunocompetent hosts, the viruses remain latent after 1stinfection. With few exceptions, ailments associated with those viruses arise in times of immune compromise, mainly in situations that bring about T cell deficiency . The family of this virus is known as Polyomaviridae viruses whose herbal hosts are ordinarily mammals and birds. the human polyomaviruses are recognized to cause respectively, hemorrhagic cystitis in recipients of bone marrow transplantation and revolutionary multifocal leukoencephalopathy in immunocompromised patients, as an example, by means of HIV infection lately, transplant nephropathy because of BKV infection has been an increasingly recognized as the cause of renal allograft failure. Polyoma virus transforms cells whilst the genome is incomplete and early functions are necessary.
5)Human cytomegalo virus
It’s associated with mucoepidermoid carcinoma. Human cytomegalovirus (CMV) infection has tropism for salivary gland ductal epithelium and establishes a chronic and lifetime contamination. Mucoepidermoid carcinoma (MEC) is the most commonplace salivary gland tumor. recent studies have proved that mouse CMV-brought on tumorigenesis that indicates histologic and molecular characteristics similar to human MEC. it’s one among members of the viral family called Herpesviridae or herpesviruses. it’s also referred to as human herpesvirus-five (HHV-five). it is able to be life-threatening for the immunocompromised, which includes HIV-infected people, organ transplant recipients, or new-born babies. Congenital cytomegalovirus contamination can lead to morbidity or even death. After contamination, HCMV remains latent within the frame all through lifestyles and can be reactivated at any time. in the end, it can cause mucoepidermoid carcinoma and probably different malignancies consisting of prostate most cancers.
it’s non enveloped virus with an icosahedral nucleocapsid containing a double stranded DNA genome. It become first isolated within the 1950s in adenoid tissue–derived cell cultures, hence the name. those 1st cell cultures were often referred to spontaneously degenerate over time. they’ve a large variety of vertebrate hosts; in people, greater than 50 distinct adenoviral serotypes were determined to motive a extensive variety of illnesses, from moderate respiratory infections in younger people (known as the commonplace cold) to life-threatening multi-organ disease in people with a weakened immune system Adenoviruses are actually recognized to be a commonplace cause of asymptomatic respiration tract infection that produces in vitro cytolysis in those tissues.
RNA Tumor viruses
1) Hepatitis C virus in addition to positive retroviruses.
2) Human T-lymphotropic virus (HTLV-1)
3) Rous sarcoma virus (RSV).
they are classified into:
1) RNA Genome – Retroviruses
2) RNA-dependent DNA polymerase encoded by virus reverse TRANSCRIPTASE
3) RNA genome by means of reverse transcriptase ? DNA genome via integrase ? integrates through Host RNA polymerase ? RNA genome
A ordinary retrovirus has: 3 genes
GAG: internal proteins
ENV: Envelope glycoprotein
POL: Enzymes :reverse transcriptase.
1- hepatitis C virus
Hepatitis B virus (HBV) and hepatitis C virus(HCV) are types of viruses that motive viral hepatitis, a type of liver contamination. Hepatitis A can also motive viral hepatitis however HBV and HCV are recognized to purpose long term infections that increase probabilities of liver cancers. worldwide, maximum liver cancers are due to HBV or HCV. Hepatitis C virus (HCV) is a small enveloped positive sense single-stranded RNA virus of the family Flaviviridae.
each HBV and HCV are spread most usually through unprotected sex, sharing needles or childbirth. Hepatitis B virus regarded to purpose flu like symptoms and jaundice, or yellowing of the eyes and skin. the general public with HBV infection get better completely and are not chronic carriers of the virus. Hepatitis C contamination won’t purpose any signs and is more likely to be chronic, that can lead to liver damage or maybe most cancers.
Antiviral tablets are obtainable to treat human beings with Hepatitis B and C. there is additionally a preventative however there is no therapeutic vaccine obtained for Hepatitis B, that’s most typically given to individuals who are vulnerable to contracting the virus, along with health care employees. there’s no vaccine to be had for the Hepatitis C virus.
2-human T-lymphotropic virus (HTLV-1)
it’s a member of human retroviruses family which is known to cause a type of cancers known as T-cell leukemia/lymphoma and HTLV-I related myelopathy/tropical spastic paralysis . at some stage in the replication procedure, the virus uses an enzyme known as reverse transcriptase, which permits the virus to alternate its RNA genes into DNA. This allows the virus genes to become included into the genes of the host cell and may reason a mutation within the host cell genes that controls cell division. this alteration can cause most cancers. HTLV-1 has been connected to a kind of lymphocytic leukemia and non-Hodgkin lymphoma referred to as adult T-cell leukemia/lymphoma (ATL). it’s common among the populations of southern Japan, Caribbean, Central Africa, and some areas in the united states of America.
Human T-lymphotrophic virus-1 is transmitted by way of unprotected intercourse, needle sharing, pregnancy, childbirth or breastfeeding. The infected person may live twenty years or more without signs and symptoms. there’s approximately a 5% hazard that the infection will lead to cancer.
3-Rous sarcoma virus (RSV)
it’s the first oncogenic virus to be defined, it lead to sarcoma (, a tumor of connective tissue) in chickens. as with every retroviruses, it opposite transcribes its RNA genome into cDNA before integration into the host DNA. Peyton Rous discovered that cancer will be precipitated in healthy chickens by means of injecting them with non cellular extract of the tumor of a ill chicken. He ground up samples of the tumor and handed the fabric through a filter with pores so satisfactory that not even micro organism could get through. however, the tumor filtrate became capable of set off cancer when injected into chickens. This was the primary demonstration of an oncogenic virus.
Virus Associated cancer types
Hepatitis B (HBV) Hepatocarcinoma
Hepatitis C (HCV) HCV is a known carcinogen, causing hepatocarcinoma
Human T-lymphotropic virus (HTLV) Adult T-cell leukaemia
Human papillomaviruses (HPV) The types 16 and 18 are associated with cancers of cervix, anus, penis, vulva/vagina, and oropharyngeal cancer.
Kaposi’s sarcoma-associated herpesvirus (HHV-8) Kaposi’s sarcoma, multi-centric Castleman’s disease and primary effusion lymphoma
Merkel cell polyomavirus (MCV) Merkel cell carcinoma
Epstein–Barr virus (EBV) Burkitt’s lymphoma, Hodgkin’s lymphoma, Post-transplant lymphoproliferative disease and Nasopharyngeal carcinoma.