During the past year, COVID-19 has taught us to appreciate the significant impact that viruses can have on our health and well-being. Human health can be impacted by many different types of virus with some causing diseases such as the common cold (rhinovirus), influenza, rabies and poliomyelitis.
The potential impact of viruses can be avoided or minimised by a person’s general good health, strength of the immune system, favourable genetics, avoidance of sources of infection and immunisation. However, on rare occasions, viral infections have been shown to lead to cancer.
Oncogenic viruses (viruses that can cause cancer) act by integration of their DNA into the host cell. This can lead to the development of cancer in a variety of ways, such as when these viral oncogenic genes impair the functioning of two families of tumour suppressor proteins, namely p53 and retinoblastoma proteins (Rb).
P53 and Rb are involved in controlling the cell division cycle by allowing time for damaged or altered DNA to the repaired and, if repair is not possible, to initiate programmed cell death or apoptosis. Interference or disabling p53 and/or Rb can instigate uncontrolled cell division leading to cancer. In addition, the cancer may arise through the action of the oncogenic virus leading to the suppression or disruption of the immune system or by the viral infection causing long-term or chronic inflammation in the susceptible organ or tissue.
In 2002 the World Health Organisation estimated that about 18% of human cancers were caused by viral infections and with the majority attributed to only seven viruses.
The prevention of viral cancers has found success in utilising vaccines to stimulate the body’s immune system to block infection. The Hepatitis B vaccine was the first vaccine recognised for its ability to help reduce the risk of liver cancer. The HPV vaccine (Gardasil) was approved by the FDA in 2006 to prevent cervical cancer in adolescent girls. Hundreds of millions of doses of Gardasil have been used in many countries around the world in preventative campaigns. Subsequent research has shown it to be effective in reducing the incidence of a number of other genital cancers in both boys and girls. The current version, Gardasil 9, protects against nine types of HPV including seven of those posing the highest risk.
Apart from vaccines the prevention of viral infections is best achieved through good hygiene, hand washing, not sharing personal items, using barrier protection during sexual activity and screening for viral infections such as HCV.
This article was written by Dr Ian Brown, ACRF Chief Scientific Officer.