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Hollow Tree Was Ebola’s Ground Zero, Scientists Say

Finger of suspicion points at insectivorous bats

Insect-eating bats that inhabited a hollow tree in a remote village in Guinea may have been the source of the world’s biggest Ebola epidemic, scientists have announced.

More than 20,000 cases of Ebola, with at least 7,800 deaths, have been recorded by the World Health Organization (WHO) since a 2-year-old boy died in the village of Meliandou in December 2013.

Reporting in the journal EMBO Molecular Medicine, German scientists investigated the circumstances surrounding that first fatality. The researchers led a 4-week field mission in Guinea in April 2014 to examine human exposure to bats, to survey local wildlife, and to capture and sample bats in Meliandou and in neighboring forests.

The finger of suspicion pointed at insectivorous bats that lived in a hollow tree 50 meters from the dead boy’s home, they said.

The Ebola virus holes up in a natural haven, or “reservoir,” among wild animals that are not affected by it. The virus can infect humans who come into contact with this source, either directly or indirectly through contact with animals that have fallen sick from it. Highly contagious, the virus is then passed among humans through contact with body fluids.

A known reservoir is the fruit bat (Epomophorus wahlbergi), a widespread tropical African species that in some countries is killed for food, offering an infection pathway to hunters and butchers of the mammal. But the role of fruit bats in the current outbreak has never been confirmed, the scientists said.

In contrast, free-tailed bats, a cousin species, have been found in laboratory tests to be able to carry the virus but not fall sick with it. That, too, would make them a reservoir, but no evidence of this has been found in the wild.

Local children not only played with the bats at the tree, they also hunted bats that roosted at village homes and grilled them for food, the scientists found. In addition, they saw no evidence of a local die-off among larger mammals, which would have been a secondary route of infection for humans. On the other hand, no trace of Ebola virus was found in any of the bats the scientists captured and whose blood was analyzed.

When the researchers came to Meliandou, they found that the bat colony had fled, for most of the tree had burned and only the stump and branches remained.

Traces of DNA found in surrounding ash and soil pointed to the previous presence of the insect-eating bats. But again, there was no presence of Ebola virus.

“The virus must be very rare in the reservoir,” said lead investigator Dr. Fabian Leendertz. “That is also obvious when you think about how many tons of bat meat is consumed every year. If more bats carried the virus, we would see outbreaks all the time. That’s one of the challenges: the virus is rare and is in a large multi-species reservoir.”

The possibility that free-tailed bats could be an Ebola vector is a worry, Leendertz said. Very little is known about how these bats live — when they migrate and reproduce, where and why they cluster, their sources of food, and so on — and only understanding this will quantify the risk for humans.

Sources: Medical Xpress; December 30, 2014; and EMBO; December 30, 2014.


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