Bats, Ebola and Climate Change, Oh My!

The last time I studied Ebola was back in public health school many years ago.  At that time the reservoir was unknown, but scientists were closing in.  The reservoir is the place where the virus hides between outbreaks.  Turns out, in the case of Ebola, it hides out in fruit bats.  Three  different species to be exact: the hammer-headed bat (Hypsignathus monstrosus),  the little collared fruit bat (Myonycteris torquata), and Franquet’s epauletted fruit bat (Epomops franqueti).

Fruit bats are, of course, mammals like you or I.  Some of them are sorta cute, looking like a chihuahua with wings (although some of them are pretty ugly too!  Google the hammer-headed bat for a look at an ugly one).  Bats are very important to many ecosystems around the planet, and to us humans.  Among many jobs, they eat literally tons of insects, and pollinate many fruit crops.  Eat a banana lately?  Yup, the banana tree was probably pollinated by a bat.  So let’s not get all “kill the bats!” crazy, please.  Bats are our friends (you can quote me on that).


Awesome Bat Facts!


So why do bats carry Ebola?

People come into close contact with fruit bats by various means,  such as, eating them,  eating animals that have contact with them, and eating fruit that the bats have drooled on.  Fruit bats have been implicated in a whole range of very nasty up and coming viral diseases, maybe because their immune systems are similar to humans or maybe because humans are encroaching on their habitat more and more, or maybe both.  Let’s look into it.


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According to an excellent article in Wired.com, there are a few possible explanations for why bats make good reservoirs of deadly human diseases.  First, bats have hyped-up immune systems.  Their over-active immune systems may have resulted from working so hard while flying around.  Imagine if you or I had wings, we’d be working hard to keep aloft without feathers.  All that hard work leads to damaged muscle tissue, which leads to damaged DNA inside the muscle cells.  Bat and human bodies have many DNA repair mechanisms.  Bats apparently have a few more that they’ve accumulated over the eons.  In bats, their DNA repair mechanisms are apparently ON all the time.  In humans it usually only turns on as needed.  These DNA repair mechanisms are what keep nasty viruses at bay inside the bat, making them less susceptible, but making them good reservoirs.

Another possible explanation is that bats generate so much body heat flying around that the heat suppresses viral activity in their bodies (sort of like having a fever all the time), so viruses never take hold inside them, but lay dormant — again, making bats good reservoirs.  The third explanation is that they have the same number of viruses that any mammal might have, but  they are just getting lots of attention lately because people are coming in close contact with them more often due to an incrreasing human population going ever deeper into forested areas.

Ebola and Climate Change

Newsweek published a recent article, “Ebola and Climate Change: Are Humans Responsible for the Severity of the Current Outbreak?”, The article took a look at that question and implied a relationship.  Ten days later, Climate Progress published an article, “Media Jumps To Conclusion On Ebola And Climate Change”, which criticized Newsweek for jumping the gun.  The gist of Newsweek’s article was that climate change is not directly driving the ongoing Ebola outbreak, but it is causing a food shortage due to irregular growing seasons, and drought.  This causes people to go further into the forest, and have closer contact with the fruit bats that carry Ebola.  They cite a 2013 report by the International Food Policy Research Institute that reports increasing climate disruption in Sierra Leone (the center of this outbreak) that has contributed to food scarcity in the region.  This combined with increasing population puts more pressure on the local environment.  So in a round about way, climate change may be a factor in this outbreak.

Climate Progress, begs to differ, stating that “there is no scientific evidence that suggests a climate link to the current Ebola outbreak.”  They quote extensively from three epidemiologists who study climate and disease; they conclude that linking Ebola and climate change is premature, basically because nobody’s really given that question a good look (I searched PubMed, the giant online research compendium for medicine and biosciences, and didn’t find any articles).  Climate Progress finishes by saying there are much more worrisome diseases on the horizon which will spread with warmer temperatures and shifting climate; diseases like malaria, dengue fever and chikungunya.

So who do we believe?

If you ask any scientist in any particular field about the link between two things, if it hasn’t been studied, they will tell you there is no KNOWN link, and that it may or may not call for investigation (depending on what they think is important).  However, it is reasonable to propose a logical idea, such as a link between bats, Ebola and climate change.  The Newsweek article in no way claimed to have the answer; they just put forth a reasonable hypothesis while Climate Progress used it as an opportunity to push their take on it.  Really the bigger issues in the case of Ebola are growing populations and destruction of forest habitat; because poor people, hungry for food and money, will inevitably exploit their local resources.  The same has happened time immemorial, around the world, and here in the U.S. in days gone by.  The end of the Newsweek article ends with a similar thought.  Deaths from Ebola, so far, are a tiny fraction of the annual deaths from diseases like cholera and malaria, which take a far greater toll every year in Africa and other places around the world.  These other dread diseases seem to be shifting around in response to changing climate, and they will likely cause more trouble in the future than they already do (future blog post!).


Make a difference and donate to these two awesome organizations…

Doctor’s Without Borders – provides field medical care, medical staff, and field hospitals.  One of the best humanitarian medical organizations around.

OxFam America – usually working to provide clean water, food, education and other services in developing countries — now providing protective gear and hospital supplies to the ebola affected countries.