Insect-eating bats implicated as Ebola outbreak source

Tree in Guinea harbored suspects in infection of first victim

A hollow tree

GROUND ZERO  This hollow tree once housed insect-eating bats that may have been the source of the Ebola epidemic. The first person to contract Ebola in the outbreak was a toddler who often played in the tree.

Fabian Leendertz

The epicenter of the Ebola epidemic may be a hollow tree in Guinea.

A 2-year-old boy named Emile Ouamouno, who is thought to be the first person to contract Ebola in this outbreak, often played with other children in the hollow tree near his home in the village of Meliandou, Guinea. That tree was inhabited by small insect-eating free-tailed bats of a species (Mops condylurus) that previous research has suggested may harbor Ebola, Fabian Leendertz of the Robert Koch Institute in Berlin and colleagues report December 30 in EMBO Molecular Medicine.

Many species of bats may spread the deadly virus, which has infected 20,171 people and killed 7,890 in the ongoing West African outbreak. Insect-eating bats often roost in houses, and people may encounter the animals more frequently as settlements push deeper into previously wild areas. To Leendertz, that suggests that the next Ebola outbreak “can start anywhere” in Africa where the bats live.

The case against the insectivorous bats is not a slam dunk. The boy was infected and died in December 2013. By the time Leendertz’s group arrived in April to track the outbreak’s source, the hollow tree had burned and the bats were gone. Villagers reported that when the tree caught fire on March 24 it started a “rain of bats.” None of the other bat species in or around the village were found to carry Ebola.

“Although [the evidence] is largely circumstantial, it’s a start for sure,” says Tony Schountz, an immunologist at Colorado State University in Fort Collins who studies hantaviruses in bats. Discovering which bat species harbor viruses will enable public health officials to teach local people how to avoid contact with the bats. “We have a good chance of modifying human behavior,” he says. “We have no chance of changing the bats.”

Getting rid of bats is not the solution, Leendertz says. “We need those bats.” Fewer bats would mean more malaria. Fruit bats are needed to pollinate many fruit crops, such as mangoes and guava.

Leendertz and colleagues from several different scientific disciplines traveled to Meliandou hoping to find the animal source, or reservoir, and learn more about how the disease might have spilled over into humans. The researchers talked to villagers, conducted wildlife surveys and collected samples from bats and material in the village. The investigation led the team to conclude that fruit bats, the prime suspects for spreading Ebola, were probably innocent. Leendertz says he can’t completely rule out fruit bats, but thinks the insect-eaters are a more likely source of the initial transmission into people.   

For one thing, Meliandou is not located near fruit bat roosting sites where the child might have come in contact with an infected animal or tainted fruit, and there is no evidence that the family ate fruit bats. The village is not typical of the rainforest hamlets where Ebola outbreaks have started in the past, Leendertz says. “There is no rainforest around.” Instead the village, composed of 31 houses, is surrounded for kilometers by rice fields and cocoa and coffee plantations.

But children often knock small, smelly, long-tailed bats that villagers call “lolibelo” from trees or roosting spots under roofs and grill the mouse-sized bats over fires. Because the boy was the first to catch Ebola, Leendertz thinks it is more likely that he got it from one of the little bats, rather than larger bats that his mother might have prepared for the family, making her more likely to contract the virus first.

 “This sort of deep epidemiology is important,” says Raina Plowright, an infectious disease ecologist at Montana State University in Bozeman. Without anthropologists and other specialists on the team, “the hypothesis of kids playing in roosting places might not have been considered,” she says.

Researchers have only indirect evidence that bats are reservoirs of Ebola, Plowright says, but the data suggest that the animals probably do harbor the virus. It will be important to learn whether the virus is present in bats at low levels all the time or if certain environmental factors trigger periodic outbreaks that might then affect people.  

Leendertz isn’t surprised that his team failed to find the Ebola virus in bats near the village. “We’re trying to trace a virus in an extremely large, multispecies population … in which the virus is extremely rare.” He and his team hope to learn more about how Ebola is transmitted among wild bats.

Editor’s note: This article was updated February 5, 2015, to remove bananas from the list of crops that fruit bats pollinate. The species of bananas cultivated in Africa are seedless and don’t need pollination.

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