Vampire bat venom that is able to dodge a victim's defence system has "tremendous potential" to treat stroke victims and people suffering from high blood pressure.

The venom of "Dracula's children" has been found to have molecules that mutate so that the bat can feed on the same victim night after night, researchers at the University of Queensland have found.

Study leader Bryan Fry said the bat venom works by evolving into a slightly different molecular composition to confuse the host body's antibody-producing ability.

The scientists said that little research had been done to find out what proteins are secreted by bat saliva glands. Previous studies have focused on two components - DSPA (a salivary activator) and draculin, a protein.

After examining the proteins, they worked out that the venom contains a novel form of DSPA and a mutant version of draculin.

Darwanian selection

Similar proteins to draculin have properties that widen blood vessels and affect blood clot ability - opening the door to develop drugs for strokes (caused by a blood clot on the brain) and high blood pressure (caused by restricted blood vessels).

"We show that vampire bat venom proteins possibly evade host immune response by the mutation of the surface chemistry," the researchers concluded.

Fry said the results showed vampire that bat venom's different types of anticoagulants cause dilation of the small arteries near the skin.

"Just as snake venom has developed rapidly to stay ahead of evolving resistance in prey, vampire bats are rapidly evolving their venom to prevent the immune system of the prey generating antibodies against the venom molecules," he said.

The bats secrete forms of the same components with tiny changes across the surface of the molecule: "This means that even if an antibody is generated against one molecule, there are a number of other ones that will sneak past the prey's defence system and keep the blood flowing. This means the same victim can be fed on night after night.

"The discovery reveals a vast array of novel molecules, which have tremendous potential to yield new treatments for stroke and high blood pressure."