Article on malaria control published by The Lancet

The below text was published online by The Lancet on 7 December 2006, and in the printed journal on 16 December (The Lancet 2006; 368:2111-2113). As copyright has been assigned to The Lancet, the text may not be reproduced without written permission from The Lancet or me.

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Comment

DDT: a polluted debate in malaria control

Allan Schapira,
Geneva, Switzerland.
a.schapira@bluewin.ch

A recent press statement from WHO about dichlorodiphenyltrichloroethane (DDT) and indoor residual spraying for malaria control¹ caused a considerable stir, despite the fact that, in terms of policy, it merely re-iterated WHO’s endorsement of DDT as a useful insecticide for malaria control, albeit in a highly promotional way. In this recurring debate, arguments for and against DDT, as before, have been heated and mainly based on considerations far removed from the realities of malaria control.

One group that criticised the WHO statement has inferred that my resignation from WHO’s Global Malaria Programme in September, 2006, was related to my opposition to its promotion of DDT.² This assumption is erroneous. For many years, WHO’s malaria-control professionals have fought hard against pressure from various sides to ensure access in malaria-endemic countries to DDT.³ Hopefully, the statement now issued by the Global Malaria Programme¹ will put an end to this debate, so that all countries that need DDT for malaria control will have unfettered access to use it in accordance with WHO guidelines and with the Stockholm Convention on Persistent Organic Pollutants, if they are signatories to the latter.

Meanwhile, remarks from the opposite camp have not lacked passion, conveying the impression that large-scale use of DDT for malaria control, so long held hostage to misguided concerns for the environment, will now save the lives of millions of people from malaria.⁴ This idea is not so simple. As pointed out in WHO’s new position statement, indoor residual spraying is an effective intervention, provided a programme infrastructure can be set up and maintained to include trained sprayers, supervisors, managers, stocks, equipment, and vehicles, that roads allow access to every village at the right time at least once a year, and that insecticides are not diverted to agriculture. The need to prevent diversion has been highlighted for DDT, but for malaria control it is equally important for other insecticides. Furthermore, especially in areas with intense and perennial transmission, it is essential to maintain the population’s long-term acceptance of spraying once or several times a year.⁵

In view of the difficulties encountered in maintaining indoor residual spraying, WHO has invested substantially in exploring other methods, especially insecticide-treated bednets. These nets have been effective in many rigorous trials,⁶ especially to reduce childhood mortality in Africa. Few trials have compared insecticide-treated nets and indoor residual spraying, but results so far suggest that the methods are more or less equal in efficacy.⁷ As pointed out by WHO,⁸ the two methods are similar in the way they work, although unlike indoor residual spraying, insecticide-treated nets can protect individual users or households. Few data exist for the use and cost-effectiveness of combining these two methods. In view of the substantial costs of prevention for the huge populations at risk, national programmes will generally need to choose one of these two methods for a specific geographical area.

The choice of insecticide is secondary. Since only pyrethroids can be used for insecticide-treated nets, and pyrethroid resistance is emerging as a constraint on their effectiveness,⁹ the fact that four classes of insecticides can be used for indoor residual spraying should be one of the main reasons justifying renewed interest in this method.

In the choice between indoor residual spraying and insecticide-treated nets, a WHO study group convened in 2004 noted that the decision should, in most cases, be based on operational factors.⁸ Because long-lasting insecticidal nets can be managed easily with minimum risk of diversion of insecticide, for most high-burden countries that have not developed an infrastructure for indoor residual spraying, the priority will be to ensure coverage of at-risk populations with such long-lasting nets. The renewed interest in indoor residual spraying could lead to interminable debates in countries about the pros and cons of DDT. Such discussions pit sectors against politicians when, in fact, a non-partisan commitment is needed desperately to protect individuals at risk of malaria with one of the two proven methods.

1 WHO. WHO gives indoor use of DDT a clean bill of health for controlling malaria. WHO promotes indoor residual spraying with insecticides as one of three main interventions to fi ght malaria. Sept 15, 2006: http://www. who.int/mediacentre/news/releases/2006/pr50/en/print.html (accessed Nov 15, 2006).

2 Pesticide Action Network North America. Global coalition of health and toxic experts demand that WHO stop irresponsible promotion of DDT. Sept 26, 2006: http://www.panna.org/resources/newsroom/stopWhoPromotionDdt20060926.dv.html (accessed Nov 15, 2006).

3 Schapira A. DDT still has a role in the fi ght against malaria. Nature 2004; 432: 439.

4 Stossel J. Hooray for DD T’s life-saving come-back. Oct 4, 2006: http://www.townhall.com/columnists/JohnStossel/2006/10/04/hooray_for_ddts_life-saving_comeback (accessed Nov 15, 2006).

5 Global Malaria Programme. Indoor residual spraying: use of indoor residual spraying for scaling up global malaria control and elimination. 2006: http://malaria.who.int/docs/IRS-position.pdf (accessed Nov 9, 2006).

6 Lengeler C. Insecticide-treated bednets and curtains for preventing malaria. Cochrane Database Syst Rev 2004; 2: CD000363.

7 Lengeler C, Sharp B. Indoor residual spraying and insecticide-treated nets. In: Murphy C, Ringheim K, Woldehanna S, Volmink J. eds. Reducing malaria’s burden: evidence of effectiveness for decision makers. Washington, DC: Global Health Council, 2003: 17–24.

8 Report of a WHO study group. Malaria vector control and personal protection. 2006: http://www.who.int/malaria/docs/WHO-TRS-936s.pdf (accessed Nov 9, 2006).

9 Etang J, Chandre F, Guillet P, Manga L. Reduced bio-efficacy of permethrin EC impregnated bednets against an Anopheles gambiae strain with oxidasebased pyrethroid tolerance. Malar J 2004; 3: 46.