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 speciesHypsignathus monstrosus, Epomops franqueti, and Myonycteris torquatahad 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.
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 areamore 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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