BERLIN (dpa) – The likely origin of the current Ebola epidemic scourging West Africa is a hollow tree in south-eastern Guinea that housed a colony of bats, an international team of scientists says.
A two-year-old boy in the Guinean village of Meliandou who is believed to have been the first Ebola death may have been infected while hunting or playing with insect-eating, free-tailed bats (Mops condylurus) that lived in the tree about 50 metres from his home.
The scientists reported the finding in the journal Embo Molecular Medicine. They say analyses suggest that a single animal-to-human transmission of a deadly new form of the viral disease just over a year ago was followed by rampant human-to-human transmission.
According to the latest statistics from the World Health Organization, the outbreak since December 2013 has killed some 8,000 people. Earlier strains of Ebola have been reported since 1976.
The research team, led by German wildlife epidemiologist Fabian Leendertz from the Berlin-based Robert Koch Institute (RKI) for disease control and prevention, undertook a four-week field mission in south-eastern Guinea – near the borders with Liberia and Sierra Leone – in April 2014.
Large fruit bats that are commonly hunted for meat in the region have widely been considered to be the “natural reservoir” of the virus but the scientists said no large colony of fruit bats existed in or nearby Meliandou.
While local men reported hunting fruit bats on occasion, the scientists said family consumption of fruit bats was an unlikely source of the boy’s infection because there were no hunters in the household and no adults were affected either before or concurrently with his case.
Great apes and small African antelopes called duikers, both susceptible hosts of the Ebola virus, are also an unlikely source, the scientists said, noting they had found no evidence of a recent decline in their populations as would be expected if they were infected.
What is more, most large game consumed in the area arrives smoked from distant regions.
Had contaminated fresh bushmeat been brought into the village, its hunter would likely have been among the first Ebola cases.
Only children and women showed symptoms or died at the beginning of the epidemic, the scientists pointed out.
During their stay in Meliandou the scientists found a gaunt tree trunk where, villagers reported, children used to frequently play with and catch small bats that they sometimes barbecued on fires.
Villagers said the tree had been set on fire in late March 2014, causing a “rain of bats” from inside. Ash and soil samples collected within and around the burned tree revealed traces of DNA – mostly stemming from bat faeces – assignable to Mops condylurus, a species shown to be able to survive Ebola infection and previously discussed as a potential source of Ebola virus outbreaks, the scientists said.
“These analyses expand the range of possible Ebola virus sources to include insectivorous bats,” the scientists wrote. They did not speculate as to whether the virus was more likely transmitted by eating an infected animal or by coming into contact with its body fluids.
Leendertz told dpa that the animal-to-human transmission that probably began the current epidemic had been an “unfortunate coincidence” since the chances of having contact with an infected animal were very slim.
“Health education initiatives should inform the public about the disease risk posed by bats but also that these animals perform crucial ecosystem services with direct and invaluable benefits to humans,” the scientists concluded.
The bats catch pests and malaria-transmitting mosquitoes, for instance.