Jungle crucial to proliferation
One theory for how the disease has been spread to humans is via fruit bats. Karesh noted that variations in rainfall have a big impact on the rate at which trees shed their branches and buds, and that this impacted the Ebola-carrying bats that eat their fruit.
"If one year, fruit is more abundant, than fruit bats will have more babies. In another, they may have to move around to find food. That could have something to do with what years you see Ebola," said Karesh.
According to the WHO, the rate of global warming has accelerated further over the last 50 years, with temperatures rising by over 0.18 degrees Celsius per decade. The prevailing scientific argument is that this has caused rainfall patterns to change and extreme weather to become more intense and frequent.
In agrarian West Africa, climate change may also be bringing humans into closer contact with virus-carrying bats, as increasing and more severe dry spells hit agricultural yields and drive humans into the forest for food.
"It could be that they (bats) have long had Ebola, but spillover to humans is more recent," wrote Melissa Leach, an academic at Sussex University, England, in a blog post for both the WHO and the Lancet medical journal this April.
"This assumes that once extensive forests in which bats lived, separately from humans, have undergone progressive deforestation under the influence of population growth, land use, and climate change. As bat habitats have fragmented and as people have moved into once-pristine forest areas, so human-bat contact has increased, making viral spillover more likely," she explained.