Climate change may worsen Ebola

Ebola outbreaks could become 60% more frequent and affect 4 times as many people as they have in recent years, owing to the effects of climate change and over-population. That’s the sombre message in Nature Communications, emerging from a new disease outbreak simulation, that Chris Smith heard about from UCL’s David Redding…

David - Ebola is a very interesting disease. It's what we call a zoonotic or animal-borne disease, so we catch this disease from contacting animals and then it spreads through human populations. What we were really interested in: can we think about the animals that have this disease where they live, and also where the people live and what conditions they live in? And if we can bring those two things together we can understand how Ebola outbreaks are likely to happen in the immediate future and in the more distant future. So what we did is that we constructed what we call a model; that is, do a very simple version of reality that hopefully still contains the important transmission processes for this disease. And then we can run that model lots and lots and lots of times to see where might be at risk, and what might happen if outbreaks happen in certain areas.

Chris - Essentially a computer simulation, then, where you can tweak numerous variables to ask what factors might be big drivers in the future?

David - Yes. So we try and build a simulation that, when we run it for present day, it matches what we do know about where outbreaks have occurred. And when we're happy this simulation is simulating reasonable scenarios, we can then think about what happens if we move this model to different environments. So for instance, where we've changed the landscape to more human-dominated landscapes. And as the climate continues to increase in warmth, how is this then going to play out in those conditions?

Chris - And when you run these scenarios, what do they predict?

David - One of the things that we predict is fewer smaller outbreaks, and they're shifting towards larger outbreaks. And that's likely to be to do with how the disease is then caught by people; there's more people, high connectivity because more people are moving, and therefore we get these bigger outbreaks.

Chris - How big is the difference that you're seeing between what we see today and the predictions made by your study, in terms of the upscale of the size of the caseload and the frequency of these outbreaks?

David - We looked at several different scenarios. In the worst-case scenarios we see a 50 to 60 percent increase in epidemics, which is what we define as outbreaks with more than 1,500 human cases. And we see about four times increase in the total number of cases per year on average.

Chris - And what about the geography over which they are manifest? Do you see an expansion of that? And if so by how much?

David - Under the best-case scenarios we see an increase of just 1 percent, so effectively the same area. Under the worst-case scenarios we're looking at a 15 or so percent increase in the area that's likely to be infected.

Chris - And what factors in the model wield the most influence? So in other words, if you're a policymaker and you're saying, “I'm going to go to Africa and I'm going to have a strategy to try to minimise the Ebola threat,” what's the top three things to target which would have the most dramatic effect turning your worst-case scenario into your best-case?

David - In our model we see the biggest effect in terms of socioeconomic scenario. We have three different scenarios: we have one where we're kind of carrying on as usual; we have one where we work cooperatively to reduce poverty, and increase education, and increase healthcare resources; and one where we start being more isolationist and trying to deal with problems on our own. We definitely see, in that more isolationist scenario, we see a large jump in the number of epidemics and the size of epidemics. That has the biggest influence in terms of our results. And so if we work together when we say, “okay let's improve the healthcare resources in these areas where we have these dangerous diseases that have the potential to spread,” not only are we going to protect from Ebola if we have better containment facilities, we're less likely to see any kind of global importations of the disease into other countries, and we're also going to protect in terms of future diseases that we don't currently know about. It's a win-win situation really if we work to improve healthcare facilities in these high-risk hotspots.