At 4:50am at the Kasanka National Park in northern Zambia, tourists watch and listen from a platform in a tree as the sound of millions of wings accompanies the sunrise.
About 10 million straw-colored fruit bats are returning from a night of feeding, some flying as far as 100km to feast on berries and figs. The animals might hold a clue to finding the cure for the Ebola epidemic that has killed more than 8,000 people in west Africa in its biggest outbreak, University of Zambia veterinary medicine school professor Aaron Mweene said. That outbreak, which is yet to be quelled, has been blamed on bats.
Researchers, including scientists from Japan’s Hokkaido University, undertook a study that found a high prevalence of Ebola antibodies in the creatures that undertake the world’s second-largest mammal migration from the Democratic Republic of the Congo to roost in Zambia, Mweene said. That indicates that they come into contact with the virus and cure themselves.
Illustration: Mountain people
“The antibodies have been found in about 10 percent of the animals; it is a significant part of the total,” Kasanka ecologist Frank Willems said in an interview in the park. “It might well be that specifically this species will form the clue to actually finding the cure for Ebola.”
The bats migrate each year to roost in an evergreen marsh ficus forest in Kasanka, about 500km northeast of Lusaka, the capital. They arrive beginning in October each year and stay until December, roosting in an area as small as 1 hectare. During the day, the average bat density in the forest is as high as 1,000 bats per square meter, as the mammals, which have an 80cm wingspan, seek protection in numbers from the raptors that eat them.
Their migration is only topped by that of Mexican free-tailed bats from the US to Mexico.
Prior to the Hokkaido University research — the results of which have yet to be officially released — Ebola antibodies had been found only once in this species, a researcher said in a e-mailed response to questions earlier this month.
South African National Institute for Communicable Diseases Center for Emerging and Zoonotic Diseases Special Pathogens Unit director Janusz Paweska wrote that the specimen was captured in Ghana’s capital, Accra, in 2008.
Ayato Takada, head of the Hokkaido team who undertook the research, declined to comment, saying that the research will be available when published.
Some scientists are skeptical.
“With viruses like Ebola and Lassa, the virus and the host — such as bats and mice — are very well-adapted to each other, having spent thousands of years together,” University of Reading virologist Ben Neuman said in an interview. “Antibodies can help, but antibodies are not usually a solution by themselves for a virus.”
Lassa fever, like Ebola, can cause hemorrhaging. The Marburg virus is also closely related to Ebola.
Trials of potential treatments using human antibodies found in survivors are under way in Guinea.
Mweene has been researching the bats since 2005 and working with the Hokkaido University researchers.
“We cannot categorically say that the cure for the Ebola virus disease lies in the bats, but we could say that surely the bats possess certain characteristics that enable them to survive the infection,” Mweene said in an e-mailed response to questions.
None of the bats were found to be infected with the virus itself.
“They will pick up the virus; they just have a very effective defense mechanism against it,” Willems said, as hippos snorted in the lake behind him.
To understand how the bats react to Ebola, scientists need to carry out experimental infections of the animals. As the virus is so dangerous, they can only do this in the highest level of biosecurity containment laboratories, Mweene said.
Africa has one only of these — the institute in Johannesburg, he said.
“The mechanisms of Ebola and Marburg virus’ natural transmission cycles still remain one of the most hunted treasures in modern virology,” Paweska said. “Plans are in place to expand our current bat colonies for experimental infection studies, but also to intensify surveillance studies, including sampling of bats at targeted sites in South Africa and other African countries.”
While bats are suspected to be natural reservoirs for Ebola, this is unproven.
The bats might also help in locating Ebola’s natural reservoir.
This year, researchers have for the first time fitted some of the animals with GPS devices to track their movements as they travel back to the Democratic Republic of the Congo, Willems said.
The batteries last about three months, which is about the time it takes for them to reach their destinations, he said.
The tracking unit comprises a collar and a transmitter on the bat’s back that is about 4cm long.
Researchers are working on solar-powered technology to allow the year-round tracking of the bats, but “for a forest animal that is nocturnal, that’s tricky,” Willems said.
Tracking might assist in providing clues about where the animals come into contact with the virus, possibly leading to its origin, he said.
While Zambia has no recorded cases of Ebola, the outbreak in west Africa is denting the reputation of the flying mammals across the continent.
The first person to contract Ebola in its most recent outbreak in west Africa might have been infected by insectivorous free-tailed bats in Guinea, according to a study published on Dec. 29 last year in the Heidelberg, Germany-based EMBO Molecular Medicine journal. In the outbreak, the virus has mostly killed people in Guinea, Sierra Leone and Liberia, the WHO has reported.
Television advertisements shown as far away as South Africa advise people not to eat bats, a delicacy in some parts of west Africa, where they are smoked, grilled or made into a soup.
Ebola’s connection with bats has already kept some people from visiting Kasanka, Willems said. He estimates that the number of bat-viewing tourists fell by as much as one-fifth last year.
Kasanka Trust Ltd, which manages the park, said in an Oct. 15 statement last year that there is “no risk” in watching the bats.
Back in the tree platform, the shrill sound of the chattering bats returning for the day fills the air. For the second straight morning, there are only two tourists witnessing the spectacle.
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