The Ebola epidemic continues to rage in west Africa, despite the fact that news coverage has all but dried up. Here, Beth Skwarecki speaks to researchers from the University of Georgia to find out if we could stop the epidemic within the year.
Although the Ebola epidemic is still raging in west Africa, US and European buzz about the disease spiked briefly and then all but disappeared, according to Google search data published in Vox’s in-depth report.
Liberia’s situation is the most promising, compared to the other two countries involved, writes Julia Belluz at Vox. Experts say that Guinea has “no discernible upward or downward trend” of cases, Sierra Leone is “the most challenging front,” and Liberia is the country closest to having the outbreak under control.
Ebola eradication is probably impossible, because the disease seems to simmer in wildlife populations, including bats, making occasional jumps into humans. Until recently, the outbreaks only killed dozens or hundreds of people before fizzling out, sometimes without another recorded case for years. The current outbreak, on the other hand, has been going on for over a year, with an official death toll of, at this writing, over 8000.
Now, a new model of the epidemic suggests that it may be under control, at least in Liberia, by mid-2015.
I spoke with John Drake, whose team at the University of Georgia studies the dynamics of groups of living things, from wildlife populations to disease epidemics. They have a paper out in PLOS Biology today describing their prediction.
What’s the best case scenario and the worst case scenario here?
The worst case is that it could be quite terrible. If the current vigilance and investment and public buy-in isn’t maintained, it could take a turn for the worse.
I don’t think the worst case scenario is a very likely outcome, because I think that the public, the community, the politicians, the health community have all been galvanised by their battle with Ebola over the second half of 2014. And they have made tremendous gains, and I think that they’re going to maintain that vigilance. And I’m optimistic that the great majority of transmission could be eliminated by the second quarter of 2015, maybe even slightly earlier.
A lot of previous models focused on R0 [the number of new infections that each infected person can cause], but yours takes other factors into account.
A lot of models are based on an ‘if everything remains the same’ kind of assumption, and all that’s changing is the number of susceptible and infectious persons in the population.
But we said, well, no! The baseline is not staying the same, because they’re building Ebola treatment units. So hospital capacity is increasing. And what effect does that have on containing the outbreak? We included that trajectory, that sequence of Ebola treatment units being constructed in the development of our model.
Another important difference is that we focused on the different sites at which persons would acquire infection, whether that was in the hospital, at a funeral, or in the community, and how that would feed back into transmission. If a person acquires the infection in the hospital, then they’re very likely to be treated in the hospital, and the contact rate would be low.
On the other hand, a person who contracted the infection in the communitymight go to the hospital and effectively be isolated from the susceptible population. But they might be treated in the community, which means a larger number of persons might be exposed. And so this places an emphasis on the willingness of potentially infected persons to seek care and be treated, and allows us to explore better what’s the possible range of outcomes based on the frequency with which patients are isolated.
Another difference is in order to make our work tractable, we took a shortcut. We said, we don’t suspect that what epidemiologists call susceptible depletion, the extent to which previously infected individuals are removed from the population and therefore causing the epidemic to be self limiting — we don’t think we’re in that situation yet. And by making the approximation that susceptible depletion was negligible, that allowed us to make further progress on emphasising the sorts of things we thought were important.
Your predictions are focused on Liberia, but the epidemic is also raging in Guinea and Sierra Leone. Do you think all three can contain it by the middle of 2015?
Our model is Liberia specific. There are differences among these countries; we don’t fully understand what those differences are.
My group decided to focus on Liberia because at the time we began this work, it’s where the epidemic was most out of control, it’s where we thought we could make the greatest contribution, and it’s where we had the best information. And we knew of other folks working particularly on Sierra Leone and Guinea.
Epidemiologically I think Sierra Leone is probably fairly similar. Transmission in Guinea seems to be a little bit different, and I think people are scratching their heads to understand first of all how is it different, and secondly what are the consequences of those differences.
I wouldn’t say the whole thing is coming to a close yet. I think that if Liberia is able to maintain their current level of response, and if they are able to prevent reinfection, re-ignition of the epidemic within Liberia, then I think we’re on a downward trend for Liberia. But it’s in a context in which there’s going to be interaction with neighbouring countries, and there’s a possibility for subsequent flare-ups, so it requires vigilance and rapid response.
I think that the response in Sierra Leone and Guinea will ultimately contain those epidemics. I think that they are working very hard to accomplish that, and eventually that will happen in those places as well. But there needs to be continued investment in those places.
What do people need to know about Ebola now?
I do think the public’s been well informed about this particular epidemic, and I think that people understand that there’s not any reason for hysteria in western Europe or in the United States or places that are contributing health professionals to try and contain this epidemic.
I think that we are learning things about how collectively the world can respond to emerging infectious diseases like this that really pose a threat not just in one region or in a particular country or in the developing world, but that actually expose us all to some level of risk. And how to mobilise our scientists and medics and policy makers in a coordinated way.
This article first appeared on PLoS Blogs and is republished under Creative Commons licence.