Tom Peto: Malaria elimination and mass drug administration
Although malaria has greatly declined in Southeast Asia this century, treating clinical cases won’t be sufficient to eliminate it from the region. Mass drug administration allows to eliminate parasites from asymptomatic carriers, and careful engagement with whole communities is key.
My name is Tom Peto, I’m an epidemiologist working for the Mahidol Oxford Tropical Research Unit and I’ve been based mostly in Cambodia working on studies of malaria elimination.
Malaria in Southeast Asia has declined massively this century, and there are targets in which all the governments are committed to eliminate malaria over the next 10 to 15 years. However just continuing the activities of malaria control, which is treating clinical cases of malaria, may not be sufficient to eliminate malaria on target. The problem is that these infections are in people who appear healthy and so they go untreated. We are now exploring in clinical trials new ways of treating these infections to interrupt transmission, one of which is known as mass drug administration, or MDA, and this is a presumptive treatment of an entire population in a geographic area to interrupt malaria transmission.
Mass drug administration is easy in theory: you just get everyone to take the medicine and there’s no one with parasites to transmit. In practice it’s quite complicated, it’s difficult to get entire communities to understand about the importance of asymptomatic infections and want to participate because you need to get entire families including children, old people, migrant workers, forest workers, everybody in the community has to take the medicine around the same time. It’s challenging but we know now that it’s been successfully done, by our group on a small scale during clinical trials in several countries and by other groups as well in different circumstances, so though I say it’s challenging it has worked when it’s been done properly.
In the last 5 or so years, there have been new lines of research that have come up in the conduct of mass drug administration. There’s now a licenced vaccine for malaria which has been used originally to save African children from dying from severe malaria, but we’re interested in our unit to re-purpose this as a vaccine which could be given at the same time as mass drug administration in Southeast Asia to prevent transmission because the vaccine would prevent new infections, whereas the MDA only cures prevalent infections at the time it’s given. Another would be to combine mass drug administration with other medicines, for example ivermectin which has the useful quality of killing mosquitoes who feed on people who’ve taken it; by taking that as well you actually affect the force of transmission in the village at the same time. Then there are new rapid diagnostic tests which are very sensitive, much more so than the existing ones, and these could be used in some places where it’s not possible to do MDA to screen and treat the asymptomatic reservoir of malaria, or given in addition after MDA to prevent malaria from being re-introduced into villages.
I think it’s important to fund this sort of research because the emergence of artemisinin resistance, and now resistance to the partner drugs used in artemisinin combination therapies, should be considered a public health emergency. In Southeast Asia at the moment we have historically low levels of malaria transmission and we have very motivated governments and organisations working to control and now eliminate malaria, and this may not be the case 5 or 10 years from now. In order to eliminate malaria, we’re going to need to do a lot of research at the same time to understand the effectiveness, the safety, the feasibility of new strategies for interrupting malaria transmission and new effective first line treatments for malaria. I think this research is important if we’re going to reach our elimination goals in the middle of the next decade.
I think this kind of applied field research has a large practical value, if we demonstrate new effective ways of attacking the asymptomatic reservoir of malaria which sustains transmission, particularly these mass drug administration studies. These are strategies which could be incorporated into malaria control and elimination programmes. Indeed, since we began working on studies of mass drug administration in Southeast Asia, I think we’ve had an influence on policy in countries and in international guidelines. MORU and partners have fed into these, providing evidence of what works and what may be effective and where it may be effective, so I think there’s a fairly immediate practical value to this research.