If you want to predict where there will be an Ebola outbreak any time soon, scientists say you should look for answers in the trees.
A new study of Ebola virus disease (EVD) outbreaks in 27 sites and 280 comparable control sites in central and West Africa, found that outbreaks that were located along the limits of the rainforest were associated with forest loss, two years before the epidemics.
Using remote sensing techniques and deforestation data for the period 2001 to 2014 in areas where EVD outbreaks had been reported since 1976, scientists investigated the relationship between deforestation and Ebola outbreaks.
TWO-YEAR TIME LAG
In the journal Scientific Reports, they reported that there was an increased probability of an EVD outbreak in sites where deforestation had occurred, two years before the outbreak. Therefore, preventing the loss of forest cover may reduce the likelihood of future outbreaks.
In all the cases, the higher the proportion of dense forest lost, the higher the likelihood that an Ebola outbreak would occur, and that there was a time lag of two years between forest loss and an outbreak.
A likely explanation is that forest loss and fragmentation allows increased contact between human and infected wildlife and this could favour the combination of ecological events that are required for viral emergence.
Ebola virus disease (EVD) is a zoonosis (disease transmitted from animals to humans) that causes severe and often fatal haemorrhagic fever in humans.
It was first identified in Africa in 1976, and is estimated to have killed over 13,000 people due to high mortality and potential for contagion.
The study suggests that there is need for interdisciplinary approaches to improve our understanding of the ecology of the virus and its hosts.
In addition, accepting the inferred links to forest cover as fundamental implies that the risk of EVD outbreaks can be curbed by reducing deforestation, and human proximity and access to recently damaged forests for two years.
Another study published in the journal Environmental Science, shows that it is not just Ebola that is linked to loss of forest cover.
Malaria too has been linked to deforestation.
In a study assessing the connection between forest loss and prevalence of the disease across 67 countries, researchers found that the connection was unmistakable and rife in every region under study.
They said that clearing forests increased the available habitat for mosquitoes in malaria-endemic countries to breed and run riot.
Particularly, felling trees stripped land of shade, leading to loss of a vital store of moisture. This in turn allowed water to pool and be heated by direct sunlight, thereby providing ideal conditions for breeding mosquitoes.
Deforestation also robbed animals which prey on mosquitoes of their habitat. And fewer animals and more mosquitoes meant that the disease would be more concentrated in human, rather than animal hosts.
Where deforestation was most severe, there were more cases of malaria, and deaths associated with the disease.