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DNA Viruses
- Epstein Barr Virus (EBV)
- First human tumour causing virus to be discovered
- Belongs to class Human Herpes Virus 4
- 2 modes of infection – Lytic, Latent cycle
- Causes Burkitt’s lymphoma – aggressive, malignant cancer characterized by a solid tumour composed of aberrant B-cells
- Hits teens and young adults by causing infectious mononucleosis
- Passed through saliva of an infected person, hence called kissing disease, sharing glass, utensils or straw
- Incubation period – 4-7 weeks
- Initial signs – sore throat, tonsillitis, fatigue, anorexia, headache, white patches in the back of throat
- Mononucleosis – enlarged spleen, may even rupture
- Burkitt’s lymphoma occurs when a person is immunocompromised with AIDS or chronic malaria. EBV persistently infects B cells causing latent infection. Affects jaws, rapidly spreads to soft tissues and parotid glands. Involves chromosomal translocation between chromosome 8 (invariably) and 14, rarely with chromosome 2 or 12. This moves c-myc oncogene on chromosome 8 downstream of immunoglobulin heavy chain gene on chromosome 14 resulting in abnormal expression of the oncogene.
- Named after Anthony Epstein and Yvonne Barr who first isolated the virus
- Kaposi’s Sarcoma
- 1st described by Moritz Kaposi in 1872
- Occurs in elderly men with an incidence ratio of 10-15 men:1 women
- Average age of onset – 50-70 years in men of Mediterranean, Middle Eastern or Eastern European ethnic descent
- Single or multiple lesions in lower extremities – ankles, soles
- 1981 – 1st reported as a part of AIDS in young homosexuals & bisexuals
- Poses problems in patients under HAART (Highly Active Anti-Retroviral Therapy) and transplant patients undergoing immunosuppressive drugs
- Belongs to class Human Herpes virus 8
- Viral DNA sequence is detected by PCR in biopsy material from patients
- <3% cells show lytic infection. mRNA transcripts of latent viral genes found in most infected host cells
- Encodes D-type cyclin, IL-6 homolog, Bcl 2 homolog etc. that help in transformation of human cells
- Hepatitis B & C Virus (HBV, HCV)
- Cause chronic hepatitis that could lead to liver cirrhosis and hepatocellular carcinoma (HCC)
- HBV – ds-DNA genome
- HCV – RNA genome, replicates in cell cytoplasm
- Both infect hepatocytes, HCV also infects B-cells
- In HCC, in tumours caused by HBV, integrated viral DNA is seen whereas in case of HCV , having an RNA genome does not contain an obvious oncogene & no integration is seen
- HCV causes chromosome instability. Rises mutation by 5-10 fold in certain genes – Ig H chains, bcl-6, p53, β-catenins
- Transmission – entry via blood or body fluids into non-immunized persons, infected needles, infected mother to baby during birth
- HBV can also be sexually transmitted
- Rate of progression from chronic hepatitis to cirrhosis to cancer is higher for HCV than HBV
- HCC – not detected until an advanced stage. Hence, liver cancer is usually fatal within a year of diagnosis
- 5th most common cancer in the world
- Hepatitis B vaccine has lowered the incidence rate. No vaccine for HCV is available as of now
- Donated blood is screened for
- HBV & HCV – US, Canada
- HBV – South East Asia
- Human Papilloma Virus
- Common among sexually active adults and adolescents
- One of the most prevalent STD of the world today
- Causes cervical cancer which becomes the major cause of death among women in developing countries and is the 2nd most common cancer among women in the world
- PAP screening programs have reduced cervical cancer mortalities
- 118 types of virus discovered. Common host is humans. Also found in other mammals & birds
- Cause benign papillomas or warts in skin of hands and soles, genitals or mucus membrane
- 3 categories :
- High risk types – cancer of cervix, vulva, vagina, anus, penis (eg., Type 16 & 18). 4-20 years latent period of infection
- Low risk types – benign tumours (eg., Types 6 & 11)
- Intermediate type – HPVs are frequently found in pre-cancerous lesions, less often cause cancers (eg., Types 31, 33, 51, 52, 83)
- Structure Of Virus
- Small, non-enveloped, icosahedral, ds-circular DNA virus, 52-55nm diameter, 8000bp
- Can infect only multiplying basal epithelium cells which are metabolically active
- Enter through cuts and abrassions
- Replication and virion assembly occurs in nucleus
Some Useful Information
- Bivalent vaccine for HPV is available that is 100% effective against persistent HPV – 16 & 18 infections. Reduces incidences of cervical cancer.
- Vaccine preparation – HPV 16 & 18 L1 genes expressed in S.cerevisiae cells in high quantities. The proteins self-assemble to give a virus – like particle (VLP) without the genome. It infects human epithelial cells of cervix and causes papillomas. Injected intramuscularly into arms.
- This vaccine is 62% efficient in females and 64% in males
- GARDASIL – Manufactured by Merck and licensed by FDA in 2006. CDC recommends 11-12 aged females to get vaccinated in order to reduce cases of cervical cancer. Several states are mandating the use of this vaccine.