Much-maligned pesticide returns to the front line.
After decades of being shunned as an environmentally damaging chemical, the pesticide DDT is once again being touted as the most effective way to fight malaria.
The World Health Organization (WHO) announced on 15 September that it will support the indoor spraying of pesticides generally, and DDT specifically, to control mosquitoes in countries with high rates of malaria. The US Agency for International Development signalled a similar shift in policy back in May.
Although these agencies never formally opposed DDT, they did not fund countries to purchase it, and instead actively promoted the use of insecticide-treated bednets. Malaria rates have continued to rise in the meantime, claiming more than a million lives a year, mostly in sub-Saharan Africa. The agencies now advocate combining the two approaches.
“I have to pinch myself a little to believe that they've done this, but I'm really, really happy they have,” says Amir Attaran, professor of law and medicine at the University of Ottawa, Canada, who has long criticized the agencies for their malaria policies.
In sharp contrast to its previous stance, the WHO also admitted for the first time that it stopped supporting DDT despite evidence of its effectiveness. “There are lots of data there, but people are so emotional about the issues,” says Arata Kochi, director of the WHO's Global Malaria Programme. “Science comes first and we must take a position based on the science and the data.”
DDT, or dichlorodiphenyltrichloroethane, is an organochlorine that is more effective, cheaper and longer-lasting than the alternatives. Fears about its use date back to the 1960s when Rachel Carson's book, Silent Spring, famously chronicled its devastating effects on the environment. In the years that followed, the United States and many European countries banned DDT.
These countries once used thousands of tonnes of the pesticide for agricultural purposes. But the use of DDT for malaria control is very different: small quantities are sprayed once or twice a year on the inside walls and ceilings of houses. Following widely publicized success with DDT in some countries such as India and South Africa, others began clamouring for the pesticide. “A lot of countries, especially in southern Africa, have become bullish about the use of DDT,” says Richard Tren of the non-profit group Africa Fighting Malaria.
Even environmental groups that once vehemently opposed DDT recognize its value in malaria control. “We still think that DDT is trouble,” says Ed Hopkins, director of the environmental quality programme at the Sierra Club, a conservation group based in San Francisco. “But in some situations, where there are no alternatives, the well controlled use of DDT is better than having millions of people die from malaria.”
Other groups say they are concerned that the agencies are not dedicating enough resources to developing longer-term alternatives to DDT. “DDT is a short-sighted response with long-term consequences,” says Paul Saoke, director of Physicians for Social Responsibility in Kenya.
Before countries can begin using DDT, the WHO must map resistance to pesticides to determine where spraying is likely to be effective and which pesticide would be best. Spraying won't work where mosquitoes bite and rest outdoors. And in most cases, mosquitoes — and with them, malaria — will return as soon as spraying stops, so the programmes require long-term commitment from both governments and donors.
But these practical hurdles can be tackled, says Kochi. “So many people took the position that even though DDT and indoor residual spraying are effective, it cannot be sustained,” he says. “My sense is, nothing is sustainable unless you decide to make it so. People make excuses.”
Kochi, who also set up the Stop TB Initiative, is largely credited with the changes in the WHO's approach. Shortly after he took this job in October 2005, he demanded that pharmaceutical companies stop marketing single-drug artemisinin medicines, and only sell combination drugs, in order to prevent resistance.
“The breath of fresh air this man represents is just tremendous,” says Attaran. “He's perfect for this job.”
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Mandavilli, A. Health agency backs use of DDT against malaria. Nature 443, 250–251 (2006). https://doi.org/10.1038/443250b