The current Ebola epidemic has led to more than 20,000 infections and almost 8,000 deaths in just one year, but how did it all start? Newly gathered data is finally yielding some important clues that point to a rather unexpected suspect. According to scientists who have been investigating a village in Guinea where the outbreak is thought to have begun, ground zero may have been a hollow tree in which a small, insectivorous bat species dwelled. Frustratingly, however, the evidence was burned when someone set fire to the tree just before the researchers arrived, meaning it is going to be very difficult to confirm their hypothesis.
Ebola is a zoonotic disease, meaning that it can be transmitted between animals and humans. It’s introduced into the human population through contact with bodily fluids of infected animals. Although previous outbreaks in humans have been linked to outbreaks in wildlife, such as gorillas and chimpanzees, no one knows which animals are the natural reservoirs for the Ebola virus. However, scientists have suspected fruit bats for some time now. This is because these animals are often hunted as a food source in Africa, so humans have plenty of contact with them, and scientists have found genetic material from Ebola virus in several fruit bat species.
That’s why a team of researchers from the Robert Koch Institute, Berlin, have been examining wildlife in the area of southeastern Guinea that the outbreak is thought to have originated, looking for signs of the disease and virus in several different animals. The first case of the outbreak is thought to be a young boy that lived in a village called Meliandou, who died of Ebola-like symptoms in December last year. Shortly after he died, several female family members caught the disease, but no men died in the early stages of the outbreak. This seemed to indicate that hunted or scavenged animals were probably not the source.
In support of this, the researchers couldn’t find any evidence of decline in wild animals such as monkeys and duikers. Furthermore, they couldn’t find direct evidence of viral infection in any of the 13 species of bat they examined. However, they did discover something interesting.
Near the village were the burnt remains of a hollow tree, in which children used to play. According to locals, when it was burning, there was a “rain of bats,” -- small bats with a long tail that the locals refer to as lolibelo. When the researchers examined the ash around the tree, they found DNA from a species that matches the locals’ description- the insectivorous, free-tailed bat M. condylurus. Apparently there may have been thousands of bats in there, and the village children used to barbeque them, so it’s possible the child may have caught or eaten an infected bat here.
The remains of the tree. Credit: Fabian Leendertz, Robert Koch Institute
Unfortunately, however, none of the bats they samples were infected, although researchers have previously found antibodies to Ebola virus in this species.
Although the idea is plausible, it can’t be proven at the moment, which is why the scientists are continuing to sample bats and other wildlife in the region in the hope that more definitive evidence can be gathered