GROUP 3 VIROLOGY PRESENTATION

1. Sheridan Chelangat. MS200/2558/2023

2. Ali Issa Haji MS200/2581/2023

3. Samuel Njubi. MS200/2563/2023

4 Priscillah Wandia. MS200/2538/2023

5. Braham Hayo. MS200/2573/2023

6. Lenz Kageto. MS200/2548/2023

Tumor Viruses

Tumor viruses are viruses capable of causing cancer by altering normal cell regulatory mechanisms.
These viruses can be either DNA or RNA viruses and contribute to a significant proportion of human
malignancies.

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1. Pathogenesis of Tumor Viruses

Tumor virus-induced carcinogenesis occurs through various mechanisms:

A. Viral Entry and Integration

The virus enters host cells via receptor-mediated endocytosis or membrane fusion.

Some viruses integrate their DNA into the host genome (e.g., Human papillomavirus, Hepatitis B
virus), while retroviruses like Human T-cell leukemia virus type 1 (HTLV-1) use reverse transcriptase to
integrate their RNA-derived DNA.

B. Disruption of Cell Cycle Regulation

Tumor viruses encode oncogenic proteins that inactivate tumor suppressor genes such as p53 and
retinoblastoma (Rb) proteins.

HPV: E6 degrades p53, and E7 inhibits Rb, leading to uncontrolled proliferation.

HBV & HCV: Induce chronic inflammation, causing DNA mutations.

C. Induction of Chronic Inflammation & Immune Evasion

Persistent viral infections cause chronic inflammation, oxidative stress, and genetic mutations,
increasing cancer risk.

Some viruses evade immune surveillance, allowing infected cells to proliferate unchecked.

D. Immortalization and Genetic Instability

Viral oncoproteins can upregulate telomerase activity, preventing cellular aging (e.g., Epstein-Barr
Virus).

Chromosomal instability and mutations accumulate over time, leading to malignant transformation.

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2. Epidemiology of Tumor Viruses

Viral infections contribute to 15-20% of human cancers globally, with a higher prevalence in
developing regions.

Risk Factors

Poor hygiene and sanitation

Multiple sexual partners

Intravenous drug use

Immunosuppression (HIV/AIDS, organ transplant patients)

Chronic infections leading to inflammation and DNA damage

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3. Clinical Presentation of Tumor Virus-Related Cancers

The presentation depends on the virus and associated malignancy.

A. Human Papillomavirus (HPV)

Asymptomatic in many cases

Genital warts (low-risk HPV types 6, 11)

Cervical intraepithelial neoplasia (CIN) → Cervical cancer (abnormal bleeding, pelvic pain)

Oropharyngeal carcinoma (sore throat, difficulty swallowing, hoarseness)

B. Hepatitis B and C Viruses (HBV, HCV)

Chronic hepatitis (fatigue, jaundice, hepatomegaly)

Liver cirrhosis (ascites, variceal bleeding)

Hepatocellular carcinoma (right upper quadrant pain, weight loss)

C. Epstein-Barr Virus (EBV)

Infectious mononucleosis (fever, pharyngitis, lymphadenopathy)

Burkitt’s lymphoma (jaw swelling in endemic African cases)

Nasopharyngeal carcinoma (epistaxis, nasal obstruction, neck mass)

D. Human T-cell Leukemia Virus-1 (HTLV-1)

Adult T-cell leukemia (fever, lymphadenopathy, skin lesions)

Neurological disorders like HTLV-1-associated myelopathy (HAM/TSP)

E. Kaposi’s Sarcoma-associated Herpesvirus (KSHV)

Kaposi’s sarcoma (purple skin lesions, lymphedema, GI involvement)

Common in immunocompromised individuals (HIV/AIDS)

F. Merkel Cell Polyomavirus (MCV)

Merkel cell carcinoma (rapidly growing, painless skin tumor)

High risk in elderly and immunosuppressed individuals

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4. Laboratory Diagnosis of Tumor Viruses

A. Serological Tests

ELISA (Enzyme-Linked Immunosorbent Assay): Detects viral antigens or antibodies (e.g., HBV, HCV,
EBV).

Western Blot: Confirms presence of viral proteins.

B. Molecular Tests

Polymerase Chain Reaction (PCR): Detects viral DNA/RNA (e.g., HPV genotyping, HBV DNA, HCV RNA).

Reverse Transcription PCR (RT-PCR): Used for RNA viruses like HCV and HTLV-1.

C. Histopathology & Immunohistochemistry

Pap smear: Screens for HPV-induced cervical dysplasia.

Liver biopsy: Identifies HBV/HCV-related cirrhosis and carcinoma.

Lymph node biopsy: Used for EBV and HTLV-1 associated lymphomas.

D. Imaging Studies

Ultrasound, CT, MRI: Detect tumors in liver, lymph nodes, or other organs.

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5. Control and Prevention of Tumor Virus-Related Cancers

A. Vaccination

HPV vaccine (Gardasil, Cervarix): Prevents cervical and other HPV-related cancers.
HBV vaccine: Reduces risk of hepatocellular carcinoma.

B. Screening Programs

Pap smear & HPV DNA testing: Early detection of cervical cancer.

Liver function tests & ultrasound: Surveillance in HBV/HCV patients.

C. Antiviral Therapy

HBV (Tenofovir, Entecavir), HCV (Sofosbuvir, Ribavirin): Reduce chronic infection and cancer risk.

HAART for HIV: Lowers KSHV-related Kaposi’s sarcoma risk.

D. Behavioral & Public Health Measures

Safe sex practices (condoms, HPV vaccination)

Blood screening for HBV, HCV, HTLV-1 before transfusions

Avoiding needle sharing (IV drug users)

Smoking and alcohol reduction (lowers co-risk for viral cancers)

E. Treatment of Virus-Associated Cancers

Surgical excision (early-stage cancers)

Radiotherapy & chemotherapy (advanced cancers)

Targeted therapy (e.g., immune checkpoint inhibitors for Merkel cell carcinoma)

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Conclusion

Tumor viruses play a significant role in global cancer burden. Understanding their pathogenesis,
epidemiology, and clinical manifestations allows for early detection, prevention, and treatment
strategies, reducing morbidity and mortality associated with virus-induced cancers.

Here are three APA 7th edition references on tumor viruses:

1. Damania, B., & Pipas, J. M. (2009). DNA tumor viruses. Springer Science & Business Media.

2. Butel, J. S. (2000). Viral carcinogenesis: Revelation of molecular mechanisms and etiology of human
disease. Carcinogenesis, 21(3), 405–426. https://doi.org/10.1093/carcin/21.3.405

3. Moore, P. S., & Chang, Y. (2010). Why do viruses cause cancer? Highlights of the first century of
human tumor virology. Nature Reviews Cancer, 10(12), 878–889. https://doi.org/10.1038/nrc2961v