Human cancer viruses are viruses that have been identified as contributing to the development of cancer in humans. Several different viruses are classified as human cancer viruses, including the following:
- Human Papillomavirus (HPV)
- Hepatitis B Virus (HBV)
- Hepatitis C Virus (HCV)
- Epstein-Barr Virus (EBV)
- Human Immunodeficiency Virus (HIV)
- Kaposi's Sarcoma-associated Herpesvirus (KSHV)
- Merkel Cell Polyomavirus (MCPyV)
A. Characteristics
- Human Papillomavirus (HPV): Over 200 types; some are high-risk strains associated with cervical and other anogenital cancers.
- Hepatitis B Virus (HBV): DNA virus; primarily affects the liver and can lead to hepatocellular carcinoma.
- Hepatitis C Virus (HCV): RNA virus; also affects the liver and can lead to liver cancer and cirrhosis.
- Epstein-Barr Virus (EBV): A herpesvirus; associated with various lymphoproliferative disorders, including Burkitt lymphoma and nasopharyngeal carcinoma.
- HIV: Weakens the immune system, increasing the risk for several types of cancers, particularly Kaposi's sarcoma and lymphomas.
- KSHV: Associated with Kaposi's sarcoma and some lymphomas.
- Merkel Cell Polyomavirus: Associated with Merkel cell carcinoma, a rare form of skin cancer.
B. Transmission
- HPV: Often transmitted through sexual contact; skin-to-skin contact can also spread non-genital sites.
- HBV: Transmitted through contact with infectious body fluids, such as blood, semen, or vaginal secretions. Routes include sexual contact and sharing needles.
- HCV: Primarily transmitted through blood-to-blood contact, typically through sharing needles or contaminated medical equipment; less commonly through sexual contact or from mother to child.
- EBV: Transmitted through saliva (often referred to as the "kissing disease") and other bodily fluids.
- HIV: Transmitted through blood, sexual contact, and from mother to child during childbirth or breastfeeding.
- KSHV: Spread through saliva, sexual contact, and possibly through blood.
- MCPyV: Thought to be transmitted via skin contact, although specifics are not fully understood.
C. Pathogenesis
- HPV: High-risk strains promote cellular transformation and can integrate their DNA into the host genome, leading to dysregulation of cell cycle regulation.
- HBV and HCV: Cause chronic liver inflammation leading to cirrhosis, which can progress to liver cancer.
- EBV: Encodes proteins that can drive cell proliferation and can lead to malignant transformation of B cells.
- HIV: Chronic infection leads to immunosuppression, increasing the likelihood of opportunistic cancers.
- KSHV: Encodes proteins that promote uncontrolled cell growth, contributing to tumorigenesis.
- MCPyV: Can integrate into the host genome, leading to uncontrolled cellular proliferation.
D. Treatment
- HPV: Vaccines (Gardasil, Cervarix) can prevent infection; treatment of lesions with surgery, cryotherapy, or other methods.
- HBV: Antiviral medications (e.g., tenofovir, entecavir) can manage the virus but do not cure it.
- HCV: Direct-acting antiviral medications can cure the infection in many cases (e.g., sofosbuvir ledipasvir).
- EBV: Treatment for cancers is usually chemotherapy or immunotherapy; no antiviral treatment specific for EBV exists.
- HIV: Antiretroviral therapy (ART) helps manage the virus and reduce the risk of associated cancers.
- KSHV: Treatment typically involves managing the symptoms and associated cancers through chemotherapy or antiviral therapy.
- MCPyV: Rare, with treatment generally focusing on the cancer it causes, usually via surgery or chemotherapy.
E. Prevention
- HPV: Vaccination before sexual activity begins is effective in preventing HPV-related cancers; safe sex practices can reduce transmission.
- HBV: Vaccination is highly effective and recommended for infants and high-risk adults; safe practices to reduce blood exposure can help prevent transmission.
- HCV: No vaccine; prevention focuses on safe injection practices, screening, and blood safety measures.
- EBV: Currently, no vaccine; practicing good hygiene and avoiding sharing drinks can reduce transmission risk.
- HIV: Use of condoms, pre-exposure prophylaxis (PrEP), and regular testing can reduce transmission risk.
- KSHV: No specific prevention measures; reducing risk factors linked to HIV can lower the risk.
- MCPyV: No vaccine or specific preventive measures; general skin protection may help reduce risk.
These viruses are significant contributors to cancer, and understanding their characteristics, transmission, pathogenesis, treatment, and prevention is crucial for cancer control and public health efforts.