DDT and Malaria

The world health community justifiably pays enormous attention to the number of deaths from Aids, which amounts to about 3 million persons a year worldwide. Malaria receives far less attention, even though it too is very deadly, causing about 11/2 million deaths per year. The world Trade Organization (WTO) declared in 1998 a "war on malaria" that aimed to cut malaria deaths in half by 2010. Instead, deaths from malaria have been increasing, not falling. The reason for the failure of this malaria war is mainly that in the name of environmentalism, the WTO and other international organizations rejected the use of an effective technique, namely spraying DDT on the walls of homes in malaria-infected areas.

What is especially disheartening about the huge number of deaths from malaria, and a fact that sharply distinguishes malaria from Aids, is that malaria deaths could be greatly reduced in a cheap way without requiring any fundamental changes in behavior, A small amount of DDT sprayed on the walls of homes in vulnerable malaria regions is highly effective in deterring malaria-bearing mosquitoes from entering these homes. Finally recognizing this, a couple of weeks ago the WTO relaxed its support of the ban on DDT, and instead supported spraying of DDT on house walls in malaria-ridden areas. This decision is likely to influence the position on DDT spraying of the World Bank, UDAID, and other relevant organizations. Some African countries, like Zambia and South Africa, which are not dependent on international support for their efforts at fighting disease, had already started to use DDT as a fundamental malaria-fighting weapon prior to the new WTO guidelines. South Africa decided to use DDT in the face of EU opposition after suffering a deadly malaria outbreak. DDT apparently helped that country greatly reduce its incidence of malaria.

DDT was developed as the first modern insecticide during World War II, and was remarkably successful in reducing deaths from malaria, typhus, and other insect-borne human diseases. DDT was extensively used worldwide in the subsequent two decades with continued success as protection against these diseases, and was employed even more extensively to rid cotton and other crops of destructive insects. In 1959, the United States alone used 80 million pounds of DDT, with the overwhelming share being devoted to spraying crops. This widespread spraying of crops with DDT generated strong opposition to its use because of evidence that DDT was destroying some wildlife.

This opposition was sparked by Rachel Carson's 1962 best selling book Silent Spring, which alleged that DDT caused cancer and harmed bird reproduction. Harm to birds and other species is pretty well documented, but after over 50 years of trying, no real evidence has been found linking DDT to cancer or other serious human diseases. In any case, by the end of 1972, DDT's use in the United States was effectively banned. That ban soon became common in all rich countries, and in most poor countries too, as they responded to pressure from international organizations and Western governments.

One unintended consequence of the DDT ban was a devastating comeback by malaria and some other diseases after they had been in retreat. Other pesticides that replaced DDT have been much less effective at reducing malaria and other diseases transmitted by insects. The USAID has been a strong advocate of mosquito bed nets as an alternative to DDT. Mosquitoes operate mainly from dusk until dawn, so netting over beds can be effective if used persistently and correctly. Unfortunately, in many African countries bed nets are not readily available, and they are often not used to protect children since poor families may only have one or two nets. Moreover, families frequently do not bother to use these nets during some of the hours when mosquitoes are still active. So while bed nets could be a useful part of an overall strategy against malaria, they are not a good substitute for DDT.

Drugs that had been effective for a while in curing malaria or preventing its occurrence have become obsolete over time as the pathogens they target mutate into resistant strains. This means that drugs used to fight malaria need to be continually updated, but unfortunately international organizations are notoriously slow at responding with newer more effective drugs.

I am an "environmentalist", but I do not believe that all reasonable cost-benefit analysis should be suspended when discussing environmental issues. The ban on using DDT in houses to fight malaria is an example of environmentalism that lost all sense of proportion. As has happened with nuclear power and in other environmental situations, exaggerated claims about negative environmental effects of DDT on humans were publicized, and these claims were further exaggerated after being picked up by the media and politicians. As a result of the hysteria against the use of DDT for any purpose, millions of lives were lost unnecessarily during the past several decades to malaria and some other insect-borne diseases. These deaths occurred only, I repeat only, because of international pressure on African and other poor countries not to use DDT and certain other pesticides in fighting malaria and other diseases caused by insect bites. The fact is that the quantities of DDT needed to be quite effective against malaria in tropical and other countries, where it is often at epidemic levels, is a tiny fraction of the amounts that had been used to rid crops of pesticides.

Opponents of DDT use in disease control should wake up and realize that there has been a health "crisis" for decades, a crisis that could have been controlled if more common sense had guided international policy. The WTO's reversal of its position to allow small amounts of DDT to be used on the walls of houses to prevent mosquitoes from entering them is a belated but welcome recognition of this continuing health crisis.

Thanks for some informative comments. Clearly, I should have said the WHO rather than the WTO. I apologize for this carelessness that is especially disturbing to me since I often write about the WTO.

I also regret that I probably exaggerated how many lives could have been saved over the years by extensive use of DDT spraying in houses. However, I am not guilty of saying that DDT spraying alone would do the job, for I did say that mosquito nets and drugs are also useful. A combination is the best approach, but these other methods are just not a good enough substitute for DDT spraying. So I do stand behind a claim that opposition to DDT spraying by many organizations caused a very large number of needless deaths from malaria.

Does the recent WHO statements supporting the use of DDT in homes reflect a change in attitudes toward DDT home use by this organization? One strong critic of my discussion points out several errors in what I said, and I am indebted to him for these corrections. However, he is inconsistent on this issue of whether the WHO has "changed" its position. On the one hand, he says that "The WHO…has always supported its use" (that is, DDT spraying), but then quotes with approval a statement by another critic of DDT spraying that "The World Health Organization's new (!) stance on DDT" (my parenthesis). "New" or not new, that is the question? I was wrong to say that the WHO had banned the use of DDT in homes until recently. However, it is accurate to say I believe that the WHO had not strongly endorsed its use until a few weeks ago, and that many donor agencies were for this reason reluctant to finance purchases of DDT for household spraying.

One commenter challenged me (and his challenge was very well answered by another commenter) as to whether DDT house spraying does pass a relevant benefit-cost criterion. Accepting his assumptions, DDT spraying would cost $12 per year per person. That amount seems to be a highly worthwhile expenditure if we relate it to estimates of the value of saving the lives of young persons even in very poor countries. Of course, a full analysis would require knowing the money value placed on their utility by people in poor countries (my paper with Rodrigo Soares and Tomas Philipson in the March 2005 issue of the American Economic Review on declines in mortality in poor countries tries to measure utility value of improved life expectancy, not improvements in GDP alone), the probabilities that such spraying would save lives or significantly improve the quality of lives, the productivity of alternative uses of these funds, such as to find an effective vaccine, and so forth. I, have not, nor has any one else to my knowledge, made these calculations, but if spraying only costs $12 per year, and it is effective in significantly cutting deaths from malaria (some commenters dispute that), to me that seems like a great use of private or public funds.