This document discusses oncoviruses, which are viruses that can cause cancer. It describes the discovery of several important oncoviruses, including avian sarcoma leukosis virus in 1908, cotton tail rabbit papillomavirus in 1933, and polyoma virus in 1957. Important human oncoviruses identified include Epstein-Barr virus in 1964 and Human T-lymphotropic virus 1 in 1980. Oncoviruses can cause mutations in host cells through a process called transformation, altering the cells' shape, growth rate, and ability to induce tumors. Oncoviruses contain oncogenes, which are genes responsible for tumor induction, and are classified as DNA viruses like papillomaviruses and hepatitis

1. ONCOGENIC VIRUSES

2. Introduction
◦ An oncovirus is a virus that can cause cancer.
◦ The viruses that produce tumours in their natural hosts or in experimental animals
Or induce malignant transformation of cells in culture, are known as oncogenic viruses.
◦ Many genera of DNA viruses are found to produce tumourswhereas only one family
Of RNA viruses (Retroviridae) can do so.
◦ These oncogenic viruses were formerly named as oncornaviruses.

3. Discovery of Viruses
1. 1908 : Ellerman and Bang first demonstrated that avian sarcoma leukosis virus could be
transmitted after cell free filtration to new chickens causing leukemia.
2 . 1933 : Richard Edwin discovered cotton tail rabbit papillomavirus or shop papillomavirus the
first mammalian tumour virus.
3. 1957: Sarah and Eddy discovered polyoma virus.

4. Discovery of Human Oncoviruses
◦ 1964: Anthony Epstein, Bert and Barr identity first human oncovirus from Burkitt lymphoma
cells.
◦ 1980: Human T-lymphtropic virus 1(HTLV 1),first human retrovirus was discovered by Bernard
and Robert.
◦ 2008: Chang and Moore develop a new method to identify cancer viruses based on computer
subtraction of human sequencs from a tumour.

5. Interaction of oncogenic viruses with
host cells
1. Oncogenic viruses cause mutation –like changes in host cells by transformation.
2. Transformation represents the various changes that accompany the conversion of a normal cell
into malignant cell.
3. Properties of cells transformed by viruses :
1. Alteration in shape.
2 . Loss of contact inhibition so that , instead of growing as monolayer, they grow piled up, one over
another, forming ‘microtumours’.
3. Appearance of new virus specified antigens
4. Increased growth rate.
5.Capacity to induce tumours in susceptible animals.

6. ONCOGENES
◦ Genes that are responsible for the induction of tumours are called ONCOGENES.
◦ Many of them not only play a important role in malignant transformation but also in normal cell
growth
◦ Viral Oncogenes( V- onc) – means the oncogenes present in viruses.
◦ Cellular Oncogens (C- onc) – are these oncogens isolated from cancer cells.

7. Classification of oncogenic virus

8. Oncogenic DNA viruses
◦ Papovaviruses.
◦ Herpes Viruses.
◦ Hepatitis B virus.
◦ Poxvirus.
◦ Adenovirus.

9. ◦ PAPOVAVIRUSES –
papilloma viruses produce wart and papilloma in their host.
Human papilloma virus(HPV) has produced lesions in female and male genital tract.
◦ HERPES VIRUS –
Herpes simplex type 2 has caused cancer of uterine cervix. Herpes simplex type 1
has caused cancer of lip.
◦ HEPATITIS B VIRUS –
Hepatitis B virus is strongly implicated in the development of hepatocellular
carcinoma.

10. ◦ POXVIRUS –
Yaba vines monkey causes cancer in monkey .The case of the virus was obtained
from the colony of rhesus monkeys in yaba.
◦ ADENOVIRUS –
Some types of human adenovirus may produce sarcoma in hasters after
experimenta inoculation.

11. Oncogenic RNA Viruses
◦ All oncogenic RNA Viruses except Hepatitis C virus belong to the family Retroviride.
◦ Oncogenic retroviruses are mainly responsible for leukaemias and sarcomas , in their host.
1. Avian sarcoma leukosis complex.
2. Murine leukosis.
3. Mammary tumour vines of mice.
4. Leukosis- sarcoma viruses of other animals.
5. Human T cell leukaemia virus (HTCV).
6. Hepatitis C virus.