Is climate change key to the spread of Ebola?

http://www.cnbc.com/id/101920921#.

Katy Barnato
Aug. 15, 2014

Ebola outbreaks may become more frequent because of climate change, scientists have warned, as the deadly disease ravages four countries across West Africa.

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Scientists are uncertain why the current epidemic has proved more serious—both in number of cases and number of deaths—than its predecessors. However, some have pointed to meteorological data to show that previous outbreaks typically occur in clusters after sudden weather changes.

Some scientists believe global warming—and the subsequent increase in extreme weather—could be a factor behind in the virus's ascendance.

"If you are going to get more severe dry spells followed by heavy rains that might lead to more outbreaks," William Karesh, the executive vice-president for health and policy at the EcoHealth Alliance, told CNBC on Thursday.

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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.

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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.

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If climate change is impacting Ebola, then it is one infectious disease among many being affected, according to Karesh.

"There are a lot of diseases that are especially affected by weather patterns—malaria, Dengue fever, diseases that are spread by tics like Lyme disease," he said.

Prior to the 2014 Ebola epidemic, the WHO had already warned that contagious diseases appeared to be on the rise—and that climate change could be a factor.

Notably, Dengue fever—a mosquito-borne disease usually found in tropical climes—has already reappeared in southern Texas, with an outbreak occurring in 2005.