The confusion is also reflected by the fact that in the past year officials at the WHO have issued contradictory directives on the use of DDT to fight malaria. On September 15, 2006, Arata Kochi, the head of the Global Malaria Programme, announced at a news conference in Washington, D.C., that DDT posed no health risk when sprayed in small quantities on the inside walls of houses, and he called for an expansion of its use to combat the mosquito-borne disease. Then on May 3, 2007, Maria Neira, director of the WHO’s public-health and environment department, said at a Dakar, Senegal, meeting of the ratifiers of the Stockholm Convention—an international treaty that went into effect in 2004 that controls the use of persistent organic pollutants like DDT—that the WHO’s goal was to reduce the use of DDT and eventually eliminate it.
South Africa claims significant success in controlling malaria since ddt was reintroduced.
Lost in all the hullabaloo is the fact that DDT has never been completely banned for use in public-health measures. The Stockholm Convention defines disease control as an “acceptable use” for DDT, and 13 countries in Africa and Asia have registered their intention to use it as such. Among them is South Africa, which claims significant success in controlling malaria since DDT was reintroduced to that country in 2000. According to South Africa’s department of health, the number of malaria cases in the country dropped by 65 percent between 2005 and 2007, and deaths from the disease fell by 73 percent. The agency attributes the decline to an increase in indoor spraying with DDT, but also to earlier surveillance and detection of the illness in malaria-prone regions and the use of a drug, artemisinin, to treat multidrug-resistant strains of the malaria parasite.
Given the fact that DDT does appear to be effective at fending off malaria mosquitoes in some places, its use would seem logical—but if applications do become more widespread, users may encounter a problem that Carson herself highlighted in Silent Spring: resistance to the insecticide by the Anopheles mosquitoes that transmit malaria, says Michael Fry. Since Silent Spring’s publication, hundreds of mosquito species have become resistant to DDT, and although the rise of resistance has slowed since the ban on the agricultural use of DDT, many mosquito populations are already immune to its effects, says Pierre Guillet, of vector control and prevention at the WHO’s Global Malaria Programme. While the main malaria vector in South Africa, Anopheles funestus, is susceptible to DDT, a secondary vector, A. arabiensis, has developed resistance to DDT and other insecticides. Elsewhere in Africa, mosquito resistance to DDT is already common. “DDT resistance in Africa as well as several other parts of the world has been acquired because of massive use of these insecticides for crop protection,” Guillet says.
That’s why Fry and others believe that a broader and better solution is one that would help humans while minimizing the impact on wildlife and the environment. That solution is a suite of techniques called integrated vector management: draining mosquito-breeding pools, spraying safer, less persistent pesticides known as permethrins, and plastering homes with mosquito-repelling lime. This last approach has been applied successfully in Mexico, which no longer uses DDT for vector control. “No single pesticide will ever solve the problem,” Fry says. “What you need to do is use a variety of different pesticides in different years to minimize the insect resistance problem. You want to use other techniques as well—wetlands management, netting, screens, repellent chemicals indoors. If you rely on a single chemical like DDT, you’re going to fail.”
