Leukaemia began in ancient bent-winged bats up to 45 million years ago, a study has found.

A blood cancer-causing virus has been found in ancient DNA traces in a breakthrough that could lead to new treatments.

The discovery provides a "missing link" in the fossil record of retroviruses - a family of viruses that date back almost half a billion years.

Known as a "deltaretrovirus", human T-lymphotropic virus 1 (HTLV-1) infects 15 to 20 million people worldwide and can cause leukaemia.