Re-Booting DDT

PALO ALTO – Microsoft co-founder Bill Gates is fascinating. So is the 19-page annual letter that describes the work of the Bill and Melinda Gates Foundation, the world’s largest philanthropy. But for someone as smart as Gates, who can afford to hire experts on any subject under the sun, some of his foundation’s strategies are baffling.

Consider his foundation’s approach to malaria, which focuses on bed nets, a low-tech, only modestly effective intervention, and on the development of a vaccine, a high-tech solution that has eluded intensive efforts for decades. This approach dismisses an old, cheap, and safe way to control the vector – the Anopheles mosquito – that spreads the disease: the chemical DDT.


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Malaria is a scourge, particularly for inhabitants of poor tropical countries. Forty-one percent of the world's population live in areas where malaria is transmitted, with 350-500 million cases each year.

The disease imposes substantial costs on individuals, families, and governments. Costs to individuals and their families include drugs, travel to and treatment at clinics, lost time at work and school, and expenses for preventive measures. Costs to governments include maintenance of health facilities, purchases of drugs and supplies, public-health interventions such as spraying insecticide or distributing insecticide-treated bed nets, and lost revenue from taxes and tourism.

Such costs are a huge economic burden on malaria-prone countries and impede their development. It has been estimated that annual economic growth in countries with a high incidence of malaria is 1.3 percentage points lower than that of other countries.

Drugs called artemisinins are safe and exhibit potent, rapid anti-malarial activity. In combination with other anti-malarials, they have been used effectively for several years to treat multiple-drug-resistant malaria. But resistance has arisen and will surely increase, so that in the absence of a vaccine, elimination of the mosquitoes that spread the disease is the key to preventing epidemics.

Unfortunately, flawed public policy limits the available options.

In 1972, on the basis of data on toxicity to fish and migrating birds (but not to humans), the United States Environmental Protection Agency banned virtually all uses of DDT, an inexpensive and effective pesticide once widely deployed to kill disease-carrying insects. DDT was subsequently banned for agricultural use worldwide under the 2001 Stockholm Convention on Persistent Organic Pollutants, which stigmatized the chemical and effectively constituted a prohibition.

A basic principle of toxicology is that the dose makes the poison. Although DDT is a (modestly) toxic substance, there is a world of difference between applying large amounts of it in the environment – as farmers did before it was banned – and using it carefully and sparingly to fight mosquitoes and other disease-carrying insects. (When it is used at all now, it is now sprayed indoors in small amounts to prevent mosquitoes from nesting.)

The regulators who banned DDT also failed to take into consideration the inadequacy of alternatives. Because it persists after spraying, DDT works far better than many pesticides now in use, some of which are toxic to fish and other aquatic organisms. With DDT unavailable, many mosquito-control authorities are depleting their budgets by repeated spraying with short-acting, marginally effective insecticides.

Moreover, even if mosquitoes become resistant to the killing effects of DDT, they are still repelled by it. An occasional dusting of window frames and doorframes is extremely effective. Bill Gates’s experts seem not to know that; the foundation’s annual letter contains the following single mention of DDT: “The world hoped in the 1950s and 1960s that [malaria] could be eliminated by killing mosquitoes with DDT, but that tactic failed when the mosquitoes evolved to be resistant to the chemical.”

Since DDT was banned, insect-borne diseases such as malaria and dengue have been on the rise. In fact, the huge toll of diseases spread by mosquitoes has led some public-health officials to rethink DDT’s use. In 2006, after roughly 50 million preventable deaths, the United Nations’ World Health Organization reversed course and endorsed the use of DDT to kill and repel Anopheles mosquitoes. Arata Kochi, the WHO official in charge of malaria said, “We must take a position based on the science and the data. One of the best tools we have against malaria is indoor residual spraying. Of the dozen or so insecticides WHO has approved as safe for house spraying, the most effective is DDT.”

But policies based on science and data have a short half-life at the UN. With a notable absence of fanfare, in May 2009 the WHO, together with the UN Environment Program, reverted to endorsing less effective methods for preventing malaria, announcing that their goal is “to achieve a 30% cut in the application of DDT worldwide by 2014 and its total phase-out by the early 2020s, if not sooner.” In the absence of effective vaccines or new anti-malarial drugs – and the funding and infrastructure to deliver them – this decision is tantamount to mass murder, a triumph of radical environmental politics over public health.

How can we drain the public-policy swamp?

First, governments should re-evaluate the voluminous data on DDT that have been compiled since the 1970’s, and they should make DDT available immediately for mosquito control indoors.

Second, governments should oppose international restrictions on DDT and withhold all funding from UN agencies that oppose the use of the “best available technology” (including DDT) to control mosquito-borne diseases.

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Third, public-health officials should embark on a campaign to educate local authorities and citizens about the DDT. People now hear only the reflexively anti-pesticide drumbeat of the environmental movement, the lamentable legacy of the benighted Rachel Carson and her acolytes.

And oh, yes, it would be helpful if the world’s greatest philanthropist were to throw his weight behind removing the stigma on DDT.