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Fruit Bats Likely Hosts of Deadly Ebola Virus

Stefan Lovgren
for National Geographic News
November 30, 2005
 
Bats eaten by people in central Africa may host the deadly Ebola virus, according to new research.

The wild reservoir of the killer virus has long been a mystery, despite a number of deadly outbreaks in humans and great apes.

Researchers have now found evidence of Ebola infection in three species of fruit bats. The bats show no symptoms of the disease, indicating that they might be spreading it.

"Fruit bats are likely the reservoirs [of Ebola]," said Eric Leroy of the Centre International de Recherches Médicales de Franceville in Gabon, who led the research. "But we can not exclude definitively that other species may harbor the Ebola virus [too]."

Understanding where the disease hides between outbreaks and how it is spread should help protect both humans and great apes from the virus.

The findings appear tomorrow in the science journal Nature.

Trapping Expeditions

The Ebola virus was named after the Ebola River in the Democratic Republic of the Congo, the site of a 1976 outbreak.

The pathogen kills anywhere from 50 to 90 percent of its human victims through massive internal bleeding. A simple handshake can transmit the disease, which has no known cure.

In the past five years, Ebola outbreaks in Gabon and the Democratic Republic of the Congo have killed 263 people in total. The outbreaks also devastated local gorilla and chimpanzee populations.

No one knows how the disease entered the first human or ape, but scientists have long suspected that bats may be spreading the virus. Earlier experiments have shown that bats survive after being injected with the Ebola virus.

In the new study, researchers went on three trapping expeditions between 2001 and 2003 in Gabon and the Republic of Congo in areas close to infected gorilla and chimpanzee carcasses.

The scientists captured and tested more than a thousand small animals, mostly bats but also some birds and small land-based vertebrates, for evidence of Ebola infection.

The researchers found that bats of three species—Hypsignathus monstrosus, Epomops franqueti, and Myonycteris torquata—had either genetic material from the Ebola virus, known as RNA sequences, or evidence of an immune response to the disease. The bats showed no symptoms themselves.

The tests indicated that "Ebola probably has spent a long time within bats … suggesting that bats might be the origin" of the virus, Leroy said.

However, the amout of viral RNA found in the bats was extremely low, and the scientists were unable to isolate the virus itself.

Wide Range

Ebola spreads rapidly and easily among humans. A typical outbreak involves a person contracting the disease from some source in the forest and then infecting family members and neighbors.

Similar transmission probably occurs among chimps and gorillas.

The 2001 and 2003 outbreaks took place over a vast area—more than 150 square miles (400 square kilometers). This suggests that the natural Ebola host could also be active over a large area.

Each of the three bat species that tested positive for Ebola has a broad geographical range that includes regions of Africa where human Ebola outbreaks occur. People in these areas are known to eat bats.

"With our findings on Ebola we hope that bat taxonomy and bio-ecology will finally develop and be funded," said Jean Paul Gonzalez of the Research Center for Emerging Viral Diseases in Nakhonpathom, Thailand.

"This group has been neglected for years because [of] the lack of funding," said Gonzalez, who co-authored the study. "The consequence is that we were not able to do efficient research on bats as a potential reservoir of emerging viral diseases, in particular."

Although there is no evidence of Ebola infection in other animals that show no symptoms of the disease, researchers say they cannot exclude the possibility that some species other than fruit bats may be the reservoir.

There is also speculation that bats could be intermediate hosts.

Leroy, the study team leader, notes that if the bats carry the virus and can spread it, the number of human cases could be reduced by educating local residents about the dangers of eating the animals.

But he says bats should not be culled because of their suspected involvement in spreading the disease.

"Absolutely not," he said. "They play an important role in the ecological chain. The risk of direct contamination is very weak. We just have to know the potential risks in the contact of bats … and take some prevention measures."

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