what are oncogenic Viruses? And oncogenic DNA & RNA viruses.
Viruses that produce tumours in their natural hosts or in experimental animals, or which induce malignant transformation of cells on culture, are known as oncogenic viruses.
TRANSFORMATION OF A NORMAL CELL INTO A MALIGNANT CELL :
Some viral agents can ‘immortalise‘ infected cells, so that they become capable of continous multiplication in culture without processing other features of malignancy.Transformation is primarily recognised by a change in the morphology of the cultured cells.
THE transformed cells are altered in shape and lose the property of ‘contact inhibition’ so that, instead of growing as monolayer , they grow piled up, one over another, forming ‘microtumours’. Foci transformation can be discerned easily and are used in the assay of oncogenic viruses, such as the Rous sarcoma virus.
- Both RNA and DNA viruses are oncogenic.
- All oncogenic RNA viruses belongs to a single family : retrovirus.
- Retroviruses are responsible for naturally occurring leukemia and sarcoma in several species of animals.
- Among DNA viruses, some herpesviruses and hepadnaviruses cause malignant tumours in their natural hosts.