Scientists trace Ebola outbreak to a tree where children play

According to research published Tuesday by the Robert Koch-Institute, fruit bats are almost certainly to blame for the current Ebola outbreak, which has claimed 7,800 lives so far. But while most outbreaks caused by a fruit bat would have someone who hunted or handled the mammal for meat to blame for the contagion, the researchers believe that this case of bat-to-human transmission was sparked by children at play.

Ebola is a zoonotic disease -- one that's spread between species. The first human cases of Ebola can indeed be traced roughly to the hunting, selling and eating of bushmeat, or wild mammals like bats and non-human primates. In parts of West Africa, where the current outbreak is at large, bushmeat still lingers despite its dangers.

But the first case of 2014's outbreak has been traced to someone who shouldn't have had much contact with bushmeat. In October, researchers reported that patient zero of the outbreak was likely a 2-year-old boy named Emile Ouamouno who lived in the Guinea village of Meliandou.

In the new study, which was published Tuesday in EMBO Molecular Medicine, researchers sleuthed around Emile's village for clues about how he'd contracted the deadly virus. They checked large local mammals, but none of them showed signs of an Ebola outbreak that could have spilled over into the human population. Bats seem more likely in this case, the researchers claim.

But that left another question: If hunting or eating bat meat had caused the first infections, why hadn't an adult -- who surely would have had more contact with the bats than a toddler who might nibble on them -- get Ebola first? It's possible to get the virus just from extended contact with an infected, living animal, but Meliandou isn't a forest -- it's a fairly modern village.

By interviewing local villagers, the researchers found their answer: A large hollow tree, often filled with colonies of bats, where children from the village are known to play. But it's important to note that the evidence that these particular bats can carry and spread Ebola is still sparse.

And as David Quammen points out at National Geographic, the implications of this theory are troubling (because the bat is so common in many areas) but raise intriguing questions as well:

The Angolan free-tailed bat is a forest creature that has become a village creature; as the great trees (including the hollow trees, like that one in Méliandou) have been felled, replaced by clearings and gardens and settlements, the bat has been forced to adapt. It has become synanthropic, closely associated with humans. Now it roosts in the hundreds beneath the thatch and metal roofs of village houses, just overhead as people eat and sleep.

With at least one case now reported in Scotland, adding to cases and deaths as far from Guinea as Spain and the United States, there's something especially ghastly about the idea that a day climbing trees might have started the outbreak's cascade through West Africa. Since all of this evidence is fairly circumstantial, the researchers will have to follow up in the lab to show once and for all that these bats could have been the culprit.