DDT:
Back from the dead in the battle against malaria
15 Sep 2006 in Regulatory Science, Regulatory Economics, Regulatory Policy
The Wall Street Journal's Betsy McKay yesterday, followed by dozens of other news outlets today, are reporting that the World Health Organization is abandoning its long-standing aversion to the use of DDT to prevent malaria infection. The story provides unique insights about the contest between science and benefit-cost analysis on the one hand, and implacable opposition to pesticides nominally based on the Precautionary Principle on the other.
McKay's Thursday article (no longer available online, and significantly revised in Friday's paper) summarizes the decision: as follows:
The announcement of new guidelines by the WHO, a public-health agency that is part of the United Nations, includes plans to spray DDT, or dichloro-diphenyl-trichloroethane, in small amounts on walls and other surfaces inside homes in areas at highest risk of malaria. The disease is carried by mosquitoes and infects as many as 500 million people a year. Malaria causes about one million deaths a year, and most of its victims are in sub-Saharan Africa and younger than five years old.
DDT has been an approved and effective malaria preventative, but Western donors refused to fund its purchase because of complaints by environmental activists. Writes McKay, "The WHO's new stance is aimed partly at encouraging even countries where DDT is banned to financially support increased use of the pesticide in areas ravaged by malaria."
Spraying has led to a dramatic reduction in malaria cases in the few countries where it has been used, including South Africa. Malaria experts say DDT is one of the cheapest and most-effective ways to prevent the disease, but the chemical must be sprayed in more than 70% of the homes in targeted areas. Nearby regions also must be sprayed with DDT to halt reinfection by mosquitoes in those areas.
WHO has a map that illustrates the extent and geographical distribution of the malaria problem, and shows how it is correlated with (and in WHO's view, causes) poverty.
Environmentalists opposed to pesticides generally oppose the use of DDT for contol of the mosquitoes that transmit malaria. McKay quotes Jay Feldman, executive director of Beyond Pesticides, saying that the WHO decision "is shortsighted and doesn't recognize the long-term problems and hazards." Says Feldman: "It behooves us to advocate the phase-out of this chemical around the world and find solutions to malaria that go to the cause of infestation." By root cause, Feldman means eliminating mosquito breeding grounds, not killing mosquitoes.
In Friday's story revision, McKay gives more play to the opposition of environmentalists like Feldman: "For public-heath officials in countries losing the fight against the disease, the new guidelines promise difficult choices between fighting malaria and protecting the environment." Why this choice would be difficult isn't entirely clear, except that poor African nations fear that rich Western nations might boycott agricultural exports from countries that spray DDT indoors.
If a benefit-cost analysis were performed comparing indoor spraying of DDT with insecticide-treated mosquito nets, it is highly likely that the DDT option would offer substantially greater net social benefits. It is both cheaper (has lower costs) and more effective at preventing malarial infection (has greater benefits). Uncertainty per se about future health risks would be insufficient to tip the scales in favor of nets. For children whose lives would be spared by DDT but not by nets, the possibility of future health risks is both speculative and immaterial.
Beyond Pesticides virulently opposes pesticides, apparently in every form. For example, on September 14 the group advised its members to oppose EPA's registration of Buzz Off™ permethrin-impregnated outdoor clothing, which is marketed by a number of upscale companies. The group worries about, among other things, synergistic effects with DEET that it says "may be linked to" Gulf War Syndrome. (Ironically, on September 12 the National Academy of Sciences issued Volume 4 of its Gulf War and Health series. "The committee found that although veterans of the first Gulf War report significantly more symptoms of illness than soldiers of the same period who were not deployed, studies have found no cluster of symptoms that constitute a syndrome unique to Gulf War veterans" [emphasis added].)
Like other environmental groups, Beyond Pesticides is an avid supporter of the Precautionary Principle, which it believes argues against the use of technologies (such as pesticides) whose long-term risks are not known with certainty. However, it's not clear that Western environmentalists' views of how to apply the Precautionary Principle in the Third World are the same as the views of Africans, Asians and Latin Americans who actually live there. From their perspective, DDT use might well be perceived as the most precautionary of all possible options.
