“Our study suggests that virus-induced memory loss could accumulate over the lifetime of an individual and eventually lead to clinical cognitive memory deficits,” says Dr Charles Howe, who reports the findings in the latest issue of the journal Neurobiology of Disease.

The viruses are called picornaviruses and infect more than 1 billion people worldwide each year.

They include the virus that causes polio, as well as colds and diarrhoea. People contract an average of two or three such infections a year.