Ebola Virus and Bats: Evolved Resistance Doesn't Prevent Infection In Some Animals, Researchers Say

Ebola outbreaks are often triggered when humans come in contact with wild animals carrying the virus. Although previous studies target bats as possible viral reservoirs, new research sheds light on the biological factors that control which bat species harbor the virus between outbreaks and how it is transmitted to humans.

The team, comprised of researchers from Albert Einstein College of Medicine, the University of Colorado-Boulder (CU-Boulder) and the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) exposed cells from four types of African bats -- two of which were previously linked to Ebola -- to several filoviruses (viruses that can cause hemorrhagic fever), including Ebola. In doing so they discovered that the African straw-colored fruit bat -- a highly migratory bat often hunted for bushmeat in West Africa -- was the only species with a resistance to the deadly virus, according to a news release.  

"Here, we show how bats have evolved to resist Ebola infection and how, in turn, the virus could have evolved to overcome that resistance," Kartik Chandran, study co-leader and associate professor of microbiology and immunology at Einstein, explained in the release.

"Unlike HIV or influenza virus, Ebola virus stays hidden in an unknown natural reservoir between outbreaks," John Dye, Viral Immunology Branch Chief at USAMRIID, added. 

Ebola infects host cells by attaching its surface glycoprotein to a host cell receptor called NPC1. To better understand the virus, researchers mapped the bat's resistance and found a single amino acid change in the NPC1 gene that essentially prevents Ebola from binding to the bat's NPC1 receptor. Therefore, the African straw-colored fruit bat was taken off the list of suspects thought to be responsible for the recent Western African epidemic.

However, researchers also found a single amino acid change in Ebola's surface glycoprotein could overcome the resistance of African straw-colored fruit bat cells to infection, suggesting such viruses could evolve to better infect a host with changes in its NPC1 sequence.

Surprisingly, the NPC1 receptor where Ebola virus attaches in bats has rapidly evolved in what researchers call an "arms race" between bats and filoviruses. This might have to do with the fact that bats have been interacting with filoviruses for longer than humans have.  "We discovered that a gene segment derived from a filovirus found its way into some bat genomes at least 25 million years ago," Dr. Chandran concluded in Einstein's release, adding this is almost twice the timespan that bats were thought to have been exposed to filoviruses.

Their study, recently published in the journal eLife, could improve public health and Ebola prevention, as well as outbreak response programs in the future. 

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