DNA analysis is giving clues to how the vampire bat can survive on blood alone.

The bat can drink up to half its weight in blood a day unlike other relatives, which dine on fruit, nectar or insects.

Blood is low in nutrients and can harbour deadly viruses.

Vampire bats have key differences in genes involved in immunity and food metabolism compared with other bats.

The researchers say the bat's gut microbes are also distinct.

They found evidence of more than 280 types of bacteria in the bat's droppings that would have made most other mammals unwell.