Battle between bats and Ebola on for 25 million years: study

Washington: Ebola virus and bats have been waging a molecular battle for survival that may have started at least 25 million years ago, according to scientists including one of Indian-origin.

The findings shed light on the biological factors that determine which bat species may harbour the virus between outbreaks in humans and how bats may transmit the virus to people.

"We knew from our previous research that Ebola virus infects host cells by attaching its surface glycoprotein to a host cell receptor called NPC1," said study co-leader Kartik Chandran, associate professor at Albert Einstein College of Medicine in US.

"Here, we show how bats have evolved to resist Ebola infection and how, in turn, the virus could have evolved to overcome that resistance," Chandran said.

Outbreaks of Ebola virus disease among humans are thought to begin when a person comes into contact with a wild animal carrying Ebola virus, a member of the family of filoviruses. "Unlike HIV or influenza virus, Ebola virus stays hidden in an unknown natural reservoir between outbreaks," said John Dye, from US Army Medical Research Institute of Infectious Diseases (USAMRIID).

Prior research points to some types of bats as possible viral reservoirs, but little is known about how Ebola virus interacts with its presumed reservoir hosts.

To learn more, the researchers exposed cells from four types of African bats (two of them previously linked to Ebola) to several filoviruses, including Ebola virus.

Cells from only one type of bat proved resistant to Ebola virus infection - the African straw-coloured fruit bat, which is commonly hunted for bushmeat in West Africa and migrates long distances.

"We mapped this resistance to a single amino acid change in the NPC1 gene of this bat. This tiny change prevents Ebola from binding to the NPC1 receptor," said Chandran.

"So the African straw-coloured fruit bat - suspected as an Ebola virus reservoir in the recent Western African epidemic - was probably not guilty," he said.

The researchers showed that a single amino acid change in Ebola's surface glycoprotein could overcome the resistance of African straw-coloured fruit bat cells to infection.

Some non-Ebola filoviruses were able to infect cells from all of the types of bats tested, including the African straw-coloured fruit bat.

The researchers genetically analysed NPC1 in 13 bat species. They found that the part of the NPC1 receptor where Ebola virus attaches has evolved rapidly in bats - more quickly than in humans and other primates.

This rapid evolution, the researchers concluded, was likely driven by a long-term co-evolutionary 'arms race' between bats and filoviruses.

"We discovered that a gene segment derived from a filovirus found its way into some bat genomes at least 25 million years ago," said Chandran.

The study was published in the journal eLife.