Keeping up with Virus Taxonomy: viruses that cause cancer
Posted on April 10, 2025 by Clare Baker
Welcome back to another edition of ‘Keeping up with Virus Taxonomy’. For this edition, we’re taking a closer look at some viruses that are linked to cancers in their hosts and the families where they belong.
Some viruses hijack the host cells machinery to replicate. In order to do this, they insert their genetic code into that of the host cell. If this affects the host’s own genetic code, this may alter the normal functioning of the cell and steer it towards becoming cancerous.
Other viruses may weaken the host's immune system, affecting its ability to detect and eliminate cancerous cells.
Papillomaviridae
Papillomaviridae is a family of viruses that primarily infect mucosal and keratinised epithelia and have been isolated from fish, reptiles, birds and mammals. They’ve had a long evolutionary history with their hosts, evolving alongside them, yet some members of the family are pathogens of their host species.
You may be familiar with the viruses in this family that are associated with cervical cancer: human papillomavirus (HPV). HPV is spread by skin-to-skin contact, and infections with genital human papillomaviruses are the most common sexually transmitted infection (STI). As papillomaviruses complete their life cycle in cells already destined for cell death, papillomaviruses are not present in the blood and are hidden from the immune system. They have also evolved a variety of mechanisms that limit the body’s antiviral defence mechanisms. They appear to effectively evade the innate (non-specialised) immune response and delay the activation of adaptive (specific) immunity. This likely plays an important role in the persistence of the virus for months or even years. A persistent infection is the main risk factor for progression towards cancer for many members of the family.
Retroviridae
While some retroviruses appear to be non-pathogenic, others are associated with a variety of diseases which include: malignancies, including certain leukaemia’s, lymphomas, sarcomas and other tumours of mesodermal origin; mammary carcinomas and carcinomas of liver, lung and kidney; autoimmune diseases; lower motor neuron diseases; several acute diseases involving tissue damage; and of course, immunodeficiencies — the most notable of which is AIDS.
Another characteristic that retroviruses share with papillomaviruses is their transmission. Members of the family Retroviridae are transmitted by sexual contact as well as blood, saliva and via direct infection of the developing embryo or perinatal routes.
Polyomaviridae
This is a family of small, non-enveloped viruses with circular dsDNA genomes of approximately 5kbp. Some members of the Polyomaviridae family are known human and veterinary pathogens that cause symptomatic infection or cancer. Much like the other virus families explored in this instalment of ‘Keeping up with Virus Taxonomy,’ polyomavirus diversification has likely been strongly influenced by divergence with their hosts.
Members of this family that are linked to cancer include: BK polyomavirus, which can cause nephropathy in renal transplant patients and is linked to haemorrhagic cystitis in allogeneic hematopoietic stem cell transplantation, has been suggested to play a role in prostate cancer; JC polyomavirus may be involved in colon and brain cancer; and Merkel cell polyomavirus, as the name suggests, is linked to Merkel cell carcinoma, a rare but aggressive skin cancer.
Despite their ability to transform cells in culture and induce tumours in animal models, other mammalian polyomaviruses do not seem to be involved in cancer in their natural hosts. One exception to this rule is Raccoon polyomavirus, which may contribute to the development of malignant brain tumours in raccoons.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for developing and maintaining a universal virus taxonomy. Known viruses are categorised into a classification scheme, taking into consideration their physical and biological properties in combination with their phylogenetic relationships.
The two-page summaries of each chapter of the ICTV Report (a free resource published by the ICTV, which provides an up-to-date description of virus taxonomy) are freely available in the Journal of General Virology and are supported by the Microbiology Society. These summaries are known as ICTV Virus Taxonomy Profiles and describe the structure, replication and taxonomy of each virus order and family.