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Is climate change key to the spread of Ebola?

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

Nearly 2,000 people have caught Ebola since the epidemic started in February. More than 1,000 people have died.

All four countries hit—Liberia, Sierra Leone, Guinea-Bissau and Nigeria—have declared public health emergencies, and the World Health Organization (WHO) has termed the outbreak "unprecedented".

Women washing along the Niger River near Babila, Guinea.
Aldo Pavan | Lonely Planet Images | Getty Images
Women washing along the Niger River near Babila, Guinea.

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.

2014 Ebola outbreak in West Africa (CDC)

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.

Cellou Binani | AFP | Getty Images

More diseases to spread?

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.

Mohamed Nureldin Abdallah, Reuters

Where else could Ebola go?

The increasing prevalence of international travel may also make the spread of diseases like Ebola more likely.

"Now that we have a billion people travelling each year, a disease in one country becomes a problem for everyone else," said Karesh.

With this in mind, Karesh said airports and other international transport hubs around the world needed to focus more on "health security".

"We have to be more careful—these same ships and airplanes that are carrying people are also accidently carry mosquitos, rats…" he said.

"We are concerned that some of these diseases might get established in some place where they could not get established before."

—By CNBC's Katy Barnato

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