A common virus may cause bladder cancer, a new study reveals. 

Researchers in the UK have used laboratory grown human bladder cells to show that the virus - called BK - could be responsible for patterns of DNA damage seen in bladder tumours.

BK virus infects most people as children and causes cold-like symptoms. The virus can remain hidden in the kidneys and reactivate if the immune system is weakened by factors such as medical treatments or old age, the authors of the study say. 

The research reveals how reactivation of BK triggers bladder cells to use specialist enzymes to destroy the virus. 

These anti-viral enzymes (called APOBECs) accidentally damage the DNA of the human bladder cells in ways that could lead to cancer. 

The main risk factor for bladder cancer is smoking, however, when scientists have examined DNA from bladder tumours, they have not found the patterns of DNA damage they would expect from smoke carcinogens. 

The DNA of bladder tumours actually carries damage that has the signature pattern of APOBEC enzymes.

“Our findings alter our understanding of the causes of bladder cancer by showing that BK virus infections are a risk factor for bladder cancer because they force bladder cells to use APOBECs that damage their DNA,” says Dr Simon Baker, from the Department of Biology at the University of York.