More than 2500 new viruses have been found by scanning DNA recovered from human and animal cells. The method that was used promises to identify countless more viruses.

There are untold thousands of species of virus, but only about 9000 have been characterised well enough for their genomes to be included in the definitive Reference Sequence database, built by a branch of the US National Institutes of Health.

A team led by Chris Buck at the National Cancer Institute in Bethesda, Maryland had previously scanned …