Hannah Summers
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| Fruit bats are immune to Ebola but carry the disease, which they can transmit to humans. Photograph: Ivan Kuzmin/Alamy |
Scientists optimistic of creating early-warning system after identifying two-year gap between clearance of forests inhabited by fruit bats and emergence of virus
Scientists studying links between the Ebola virus and deforestation have made a breakthrough that could lead to the development of an early warning system for outbreaks.
Existing research into how the disease could be spread from animals to humans found Ebola hotspots matched deforestation patterns in west Africa.
But now experts have discovered a striking correlation between forest loss and the timing of outbreaks, which could in future make it possible to identify areas at risk more effectively.
John Emmanuel Fa, a senior associate at the Centre for International Forestry Research, was among those involved in the research, published on Monday in Nature’s online journal Scientific Reports.
“We found a strong link between deforestation and the timings of outbreaks that has not been shown before,” said Fa.
The study examined forest loss over different time periods in relation to Ebola outbreaks in the Congo basin. Areas not affected by the disease were also investigated.
“Statistically we found a very strong link between forest loss two years before an outbreak occurring,” said Fa, a professor at Manchester Metropolitan University. “So there is two-year lag between trees being cut down and Ebola taking hold in that location.
“Establishing a particular time period when these events of forest loss may be affecting the transmission of the virus is important, because it means we can actually set up early warning systems.”
He added: “Through the use of satellite imaging we have been able to closely monitor forest cover throughout the Congo basin and west Africa in order to pinpoint areas vulnerable to future outbreaks.”
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| Illegal rainforest logging in Western Area, Sierra Leone. Scientists believe forest loss may affect Ebola transmission. Photograph: Joerg Boethling/Alamy |
The Ebola virus is a zoonosis – a disease that can be transmitted to people from animals – and causes severe and often fatal hemorrhagic fever in humans.
First identified in Africa in 1976, Ebola is estimated to have killed roughly 13,000 people.
Initial outbreaks occurred in remote villages in central Africa, near tropical rainforests. The 2014–2016 outbreak in west Africa involved major urban areas as well as rural ones.
The World Health Organization estimates that more than 11,000 people died in west African countries when a new strain of the disease, causing internal and external bleeding, broke out in 2014.
Early rehydration treatment can improve survival rates but, as yet, there is no licensed treatment proven to cure the virus. A range of blood, immunological and drug therapies are under development.
Increased human activity and deforestation in previously untouched areas are among the shared characteristics of many Ebola outbreaks, according to scientists, who point out that such factors have brought people into closer contact with rare disease strains.
First contact leading to an outbreak usually occurs in remote, rural communities where a victim handles an infected animal carcass. One outbreak in Ivory Coast was sparked when an ethologist touched an infected dead chimpanzee. Other cases, in Gabon and Congo-Brazzaville, were linked to the deaths of forest gorillas.
West Africa, where land is being cleared at an increasing rate to grow cocoa and palm oil, has one of the world’s highest rates of deforestation.
“The increase in Ebola outbreaks since 1994 is frequently associated with drastic changes in forest ecosystems in tropical Africa,” wrote researchers in a 2012 study in the Onderstepoort Journal of Veterinary Research.
“Extensive deforestation and human activities in the depth of the forests may have prompted direct or indirect contact between humans and a natural reservoir of the virus.”
Scientists have pointed to fruit bats as Ebola’s reservoir host – a reservoir species being one that is immune to a disease but can transmit it.
Fruit bat populations grow in fragmented forest conditions. The destruction of their natural habitat has driven them to approach human settlements in search of food, spreading the disease.
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| A man walks past bushmeat in Bata, Equatorial Guinea. Monkey and bat bushmeat has been linked to the spread of the Ebola virus. Photograph: Carl de Souza/AFP/Getty Images |
Recent research has indicated that there could be other species, including rodents and antelopes, involved in transmission of the virus from animals to humans.
The authors of the new study said that, while more work is needed to identify the mechanisms of transmission, existing information on reservoir species is useful when used alongside data collected from tracking deforestation.
Fa, who worked with multi-national partners including the University of Malaga, said: “We are piecing together what we know about potential reservoir species alongside the rate of forest loss in order to develop a system that will tell governments throughout the world – and certainly those within these particular African countries – which areas are at high risk.
“Obviously there is a lot more work to be done, but the hope is we can start to hone in on highlighting the areas most susceptible to outbreaks and mobilise resources so these locations are better protected.”
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