One of our greatest nightmares have come alive. Researchers from the Federal University of Pernambuco in Brazil revealed that for the first time, a South American species of hairy-legged vampire bat started to feed on human blood.

According to the researchers' paper, which was published in the journal Acta Chiropterologica, based on their analysis, three out of 70 feces samples from vampire bats, Diphylla ecaudat, of Catimbau National Park in Brazil contained traces of human blood.

New Scientist said that these bats are used to feeding in big birds' blood, which is rich in fat, that is why the researchers were so surprised to find traces of human blood in the bat's DNA.

"We were quite surprised," says Enrico Bernard, lead author of the study, in an interview with New Scientist. "This species isn't adapted to feed on the blood of mammals."

So why are these bats consuming protein-rich mammal blood?

"The record of humans as prey and the absence of blood from native species may reflect a low availability of wild birds in the study site, reinforcing the impact of human activities on local ecological processes," the study's authors wrote in the paper.

Basically, the bats' favorite food such as guans and tinamous are being driven away by the increasing urbanization. These has pushed bats to look for a different source of food.

The alarming prospect is not just the thought of hungry bats thirsting for human blood. It is also worrisome because it could lead to the spread of disease, as vampire bats are known to be major transmitters of rabies.

IB Times noted in a report that in northern Brazil, bats, which transmitted rabies to humans, killed 23 people within two months in 2005. A total of 55 cases of rabies in humans were reported in the Amazon region.

Scientists are yet to figure out how the bats are able to adapt quickly to their change in diet. According to Daily Mail, previous studies have shown that bats would rather die than sucking blood from pigs and other mammals.