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Malaria Control vs. Elimination: A Conversation with David L. Smith

Malaria Control vs. Elimination: A Conversation with David L. Smith

It’s been a busy few weeks in the field of malaria research.  October 29th saw the launch of the Lancet Series on Malaria Elimination–a series of four papers focusing on the feasibility of elimination across contexts.  On November 6th, the Roll Back Malaria Partnership released the 5th report in its Progress and Impact Series, Mathematical Modelling to Support Malaria Control and Elimination.  The report was launched at the American Society of Tropical Medicine and Hygiene annual meeting in Atlanta, Georgia.

A major focus of these papers is how best to use data to inform malaria intervention strategies going forward, including when to move from control to elimination.  CDDEP senior fellow David L. Smith contributed substantially to both projects, so we asked him a few questions about his research, focusing on the factors that need to be considered when transitioning to an elimination strategy, the role of spatial data in considering such a decision, and the relative feasibility of elimination in countries around the globe.

What s the difference between a control program and an elimination program and where did that distinction come from?

DS: Control, elimination, and eradication there s some vagueness to these terms.  Control means that you re doing something to try to reduce malaria transmission or reduce the burden–it s not very specific.  There s a notion that control means that you ve reduced malaria to a point where it s no longer a major public health burden, but that s a very specific kind of end point for control that isn t necessarily well-defined nor is it universally used. Nobody s ever agreed about how low you need to go: if you ve reduced malaria below 1% prevalence, then you ve achieved control. When we talk about malaria elimination for countries, we mean that they ve ended endemic transmission and they ve done something to control malaria across their borders so that it s almost always absent.  We have an essay on the definition of elimination in Malaria Journal.  It gives you some historical overview of what definitions mean.

In the Lancet studies you talk about both technical and operational factors affecting the feasibility of elimination.  Can you describe those further?

DS: Technical feasibility asks, is it possible to interrupt transmission by deploying a set of existing interventions with sufficient intensity?  So, if you gave everyone a net, sprayed every house inside with a pesticide that kills mosquitoes that transmit malaria, and you made sure everybody had prompt access to drugs, would that be enough to achieve elimination?  Or if you had another set of interventions you wanted to look at, like larval control, would that get you to zero?  Operational feasibility is based on the output of your technical feasibility assessment.  For instance, you re guessing that achieving elimination in your country would require 90% or greater coverage with ITNs and that would have to be sustained for 15 years.  The next question is, do you have all of the infrastructure in place, and the malaria personnel and medical personnel in place to actually carry out that mission?   Can you actually do what s required for elimination, and is that believable?  So you can imagine a country like Haiti, that doesn t have much malaria the technical  requirements for elimination are actually quite low but operationally it s a mess.  To clarify, in this paper we re looking at the relative feasibility of achieving elimination for all of these countries, and we don t necessarily say anything about the overall feasibility.

How have decisions to move to elimination strategies, on a national level, been made in the past?

DS: Very recently Zanzibar completed a formal feasibility assessment, and they were the beneficiary of some very good technical assistance and a lot of money, including from the president s malaria initiative.  The WHO had always recommended that countries go through a feasibility assessment before embarking on an elimination campaign, but as far as we can tell no one before Zanzibar had ever actually done one, or at least not in this way technically assessing what it would take, and then assessing the operational capacity in place to do it. And the decisions to go for elimination have often been made for other reasons and sometimes, sadly to say, without any assessment.  Maybe an announcement to go for malaria elimination was made for the political expedience of it.  Without naming names, many countries in Africa have declared that they intend to eliminate malaria very soon, and the dates that they ve announced are simply not possible.

So, broadly speaking, what did your research find in terms of the relative feasibility of elimination?

DS: The broadest results were that most of the countries that were very close to achieving elimination were in the Americas.  Most of the countries where malaria still exists in the Americas have very low levels of prevalence and also seem to be in very good shape operationally.  If you look at Figure 3 [in this paper], you notice that the Americas are mostly concentrated in the lower left-hand corner, with a few exceptions. Intermediate is Southeast Asia and most difficult is Africa.  Most countries in Africa have the dual problem of having highly endemic malaria and poor governance.  There are some of the exceptions in Africa, and they are countries with reasonably well-functioning governments, such as Sao Tome and Principe, Swaziland, Botswana, Rwanda, South Africa.  But the majority of the African countries are up in that top right-hand corner, which is only to say that there are some serious barriers, both technically and operationally, to elimination in Africa, at least at the present time.  The world does change this is the current status of what we assessed to be the relative feasibilities of these countries in their capacities to go for elimination.

Finally, can you talk about directions for future research and how you see the spatial data that you re using playing a role in these kinds of feasibility assessments?

DS: The Malaria Atlas Project has assembled a vast database describing malaria endemicity, and we re about ready to update that for this next year.  In the initial iteration there were some 8,000 studies included, and in the next iteration, there will be more than 20,000 studies included, so the amount of data that s feeding into these maps has gone up substantially. The important thing is that as time goes on, we hope to see these data used more and more to have individual countries assess their own technical and operational feasibility of elimination.  Part of that will involve coming up with some better algorithms to help countries stratify transmission based on endemicity this is in the works right now and having stratified transmission, coming up with better datasets describing the outcomes of malaria control elsewhere. Ideally we would have a dataset describing malaria before scaling-up, malaria intervention coverages, and then malaria after scaling up.  The more datasets we have like that in a few places, the greater confidence we can put on our predictions in other places. And then also the other part is not just to have people own a net, for instance, but to have them use it there are great differences in the amount people use their nets.  I m afraid that right now the consensus is that with our existing tools, malaria elimination remains out of reach for most African countries, technically. I would even go so far as to say that in the sense that people mean malaria control reducing the burden of malaria to a point where it s not a major burden on the public health we don t actually have the tools in place to do that either.  In some places, malaria transmission is just so intense that if you threw everything you had at it, you would still have an awful lot of malaria, and it would actually still be a major burden on the public health.  We don t actually know, with a great deal of confidence, how many places in the world actually look like that, but enough of Africa remains in that situation, and transmission in those places would make it difficult for places nearby to achieve elimination.  It s going to take a fair amount of coordination and effort to eliminate malaria, or even control it, in Africa.  Figuring out what to do about that is one of the most important problems to contend with.                 


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