One of the many unsolved riddles about the Ebola virus is where the deadly organism hides in between outbreaks in humans. For the first time, virologists have found traces of the virus's genetic material in small, ground-dwelling mammals near areas of previous epidemics. Experts are excited about the findings, announced yesterday, but point out that it is still too early to celebrate the discovery of the Ebola reservoir.
Ebola, which first surfaced in 1976 in Congo and Sudan, causes vomiting, diarrhea, and copious internal and external bleeding. The virus kills 85% of its victims; there is no known treatment. Recent epidemics have spurred a fervent search for an animal host that might support the virus, so far to no avail. Although many species can be infected experimentally with Ebola, those captured in the wild have not had detectable levels of the virus. Some researchers speculate that the animal reservoir must be in a secluded area--deep in a rain forest, perhaps, or high in a tree canopy--where animals have not been sampled.
Unconvinced that local animals were spared by Ebola, Marc Colyn of the French National Center for Scientific Research in Rennes looked at sites near previous outbreaks of the disease. His team screened 242 animals, including several species of rodents, shrews, and bats, captured in the Central African Republic. They detected no live virus or antigens to the virus, but when they used a more sensitive screen--the polymerase chain reaction--they managed to pull fragments of the Ebola genome from seven animals: one shrew and six rodents from three different species. Then, when the researchers placed spleen tissue slices from these animals under the electron microscope, they saw tubular structures that looked exactly like the inner core of Ebola virus particles. "These structures are most likely defective [virus] particles that don't contain the full-length Ebola genome," says Vincent Deubel of the Pasteur Institute in Paris, who announced his group's findings at an institute retreat.
"This is quite exciting," says virologist Albert Osterhaus of the Erasmus University Hospital in Rotterdam. It is still unclear whether these particles, if confirmed to be Ebola, indicate that the animals could harbor infectious virus, he says. But the study suggests that "animals in a much more accessible habitat [than the deep rain forest] have definitely been in contact with Ebola," says Osterhaus.