What are oncogenic viruses?
All viruses that can cause tumors in humans or animals or malignant transformation of cells in vitro are called oncogenic viruses, which consist of two types of oncogenic viruses, RNA and DNA. Five conditions must be met to determine whether a virus is oncogenic:
1. The viral infection precedes the development of the tumor.
2. The virus, viral nucleic acid and viral antigen are found in the tumor.
3. The tumor cells cultured in vitro can produce the corresponding virus or viral antigen.
4. Viruses can convert normal cells into malignant cells and induce tumors in animal experiments.
5. Prevention of viral infections with immune intervention can reduce the incidence of tumors.
It is currently believed that tumors caused by viral infections account for 20% of the overall tumor incidence, and for some tumors such as liver cancer and cervical cancer, viral infections are the main causative agent for their development. Below we list several common viruses that cause tumor development.
1.Polyomavirus (SV40) is a virus commonly found in mice, first isolated from the kidney cells of rhesus monkeys, and its widespread presence in different species of mammals.
2.EBV: is the etiology of a variety of tumors, belonging to the genus Herpesvirus, can cause infectious mononucleosis, nasopharyngeal carcinoma, African Burkitt’s lymphoma and other lymphoproliferative diseases.
3.HPV virus, most subtypes can cause benign tumors such as condyloma acuminata, but there are two subtypes (HPV16 and HPV18) of related genes can induce cervical cancer.
4.Hepatitis B virus infection is significantly associated with the occurrence of liver cancer.
5.Adenovirus is a common respiratory virus which can cause cell transformation and its tumorigenic effect is caused by E1A and E1B genes of highly tumorigenic strains.