“These bats roost in caves, but there are very few caves in Bangladesh, so we put up mist nets outside old ruins that looked like something out of ‘Indiana Jones,’ ” he said. “In the evenings, they would come out to forage.” The team would untangle the bats, draw blood and take saliva, urine and fecal samples, and release them.

Five of them — all from the Rousettus leschenaultia species — reacted to tests for antibodies to Zaire Ebola virus. The researchers did not find any virus itself, so it was not possible to do genetic sequencing and see exactly how close the match to the African strain was.

Although closely related species of fruit bats are found in Africa, India and China, their territories do not overlap and these bats don’t migrate long distances, Dr. Olival said, so it was likely the virus had been in a bat ancestor species for millenniums. A related virus, Ebola Reston, which is not known to sicken humans, has been found in Philippines fruit bats, and an “Ebola-like” virus has been found in insect-eating bats in Spain. But the match in Bangladesh was closest to Zaire Ebola.

Ebola was at first thought to be a gorilla virus, because human outbreaks began after people ate the bodies of dead gorillas. But scientists believe that bats are the natural reservoir and that primates may get infected by eating fruit that bats have drooled or defecated on.