The global campaign to eradicate malaria in the 1950s and '60s successfully vanquished the disease from the United States and Europe and substantially reduced it in others – in India and Sri Lanka, for instance, malaria cases decreased by 99 percent. Malaria transmission was nearly wiped out in the subtropics, and it was significantly reined in in parts of the Soviet Union, Latin America, and Asia.
About the insecticide that served as a cornerstone of the campaign, the National Academy of Sciences wrote in 1970: "To only a few chemicals does man owe as great a debt." But the same insecticide has become one of today's most infamous chemicals. It is DDT.
The campaign fizzled out in the late 1960s; DDT went on to be banned in the United States in 1972. The reasons for ending a winning battle against malaria were many and complicated, and depend on what sources you read: the development of alternative insecticides, environmental concerns, cost, community opposition to spraying of their houses, mosquitoes' increasing resistance to DDT, donor disillusionment, and loss of political willpower may all have played a role.
The effects, however, were clear: many national malaria control programs collapsed and the disease resurged in various countries, including Sri Lanka, Madagascar, South Africa and Belize. Some countries continued to use DDT for house spraying, like Mexico, where the rate of malaria infection was inversely correlated with DDT use throughout the 1980s. The WHO began advocating detection and treatment of malaria over vector control, i.e., killing mosquitoes. And some developing countries abandoned it because they perceived, rightly or not, that trade and charity from industrialized nations were dependent on their following suit.
Malaria Today
An estimated 350 to 500 million people are clinically diagnosed with malaria each year and more than one million die from it. Over 90 percent of those fatal malaria cases occur in Africa, the vast majority among children under age 5.
Despite localized successes in controlling malaria since the global eradication campaign ended, worldwide, disease and death from malaria have been increasing over the last two decades. There is currently no vaccine. According to the WHO, malaria is one of the most devastating global health problems of our time.
Global malaria distribution, 2003
Source: 'Malaria and Children,' UNICEF 2007
DDT's Human and Environmental Effects
The controversy surrounding DDT is unmatched by any other insecticide, making it difficult to parse out the legitimate concerns from the hyperbolic. And the amount of DDT used in residential spraying is far less than that used for agriculture in the past. But the same qualities that make DDT a powerful tool against malaria make it potentially toxic to many other insects, to animals, and potentially to humans.
- Effects on Environment
DDT persists for decades in the environment and it bioaccumulates, meaning animals at the top of the food chain carry the highest dose. It is especially toxic to fish, aquatic invertebrates and insects, including non-target beneficial insects. Its metabolite, DDE, has been shown to significantly thin eggshells of some bird species, including the bald eagle, peregrine falcon, and brown pelican, which were all listed as endangered or threatened species in the late 1960s and early 1970s.
Evidence of health effects aren't as well demonstrated as environmental effects, but are serious enough that according to the EPA, DDT is considered a "probable human carcinogen," based on liver cancers produced in animals by the chemical.
Other reports are more skeptical. Hundreds of millions of people have so far been exposed to raised concentrations of DDT through occupational or residential exposure, but no study linking DDT to health problems has been peer-reviewed and independently replicated. Studies on DDT's contribution to cancer have yielded mixed results. DDT has been found in higher concentration in the blood of sprayers and members of sprayed households than control populations, and it may be passed in milk to infants. Some studies indicate that raised DDE leads to premature birth and early weaning, but other studies have found no association.
A Changing Landscape
These fears have made DDT a troubled part of international malaria efforts, though it seems to be gaining acceptance. The WHO, which once actively discouraged the chemical, reversed its policy in 2006 and now recommends DDT use in a variety of circumstances. Dr. Arata Kochi, Director of WHO's Global Malaria Programme, has said that "of the dozen insecticides WHO has approved for house spraying, the most effective is DDT." And some environmental groups, including Endangered Wildlife Trust, Sierra Club, and Environmental Defense, now endorse the indoor spraying of DDT for malaria control.
DDT is also incredibly affordable, one of the reasons USAID has recently begun supporting its use. "The fact is that DDT is more effective and less expensive than many other insecticides in many situations," says the organization's brief on malaria.
But DDT's stigma has been hard to leave behind. As of 2006, 17 African countries were using indoor spraying of insecticides to fight malaria; only 10 of these were using DDT. DDT's environmental and health reputation has played a role in its disuse, as has donor preference for bednets over indoor spraying. But so has another less obvious factor: trade. Whether by illegal diversion or innocent drift, some DDT purposed for malaria has turned up in crops. In Kenya, fears of lost trade drove the continued avoidance of DDT, since the European Union and the United States won't import crops that test positive for even minuscule amounts of banned chemicals, including DDT. A similar situation is playing itself out in Uganda now, where a group of farmers and agricultural exporters have taken the government to court to stop DDT spraying for malaria control, saying that it threatens their exports to western countries.
One Tool
In the end, DDT won't work everywhere, as emphasized in a statement by the African Medical and Research Foundation: spraying of houses requires a government willing and able to coordinate complex logistics, and the high level of migration and displacement in many parts of Africa makes bednets more portable and long-term solutions than insecticide spraying. Better alternatives in both bednets and insecticides are being developed.
For now, though, DDT – when used in small amounts and for its intended purpose – is one of the most promising tools in the battle against malaria. Better enforcing its use and at the same time encouraging more countries to adopt spraying may be part of turning the tide in our losing battle against malaria.
Top photo by trebol-a via Flickr
RELATED LINKS:
The DDT Debate Within the Malaria Community
DDT and Malaria Interactive Module
EarthTrends
News: "Hopeful Progress in Malaria Prevention"
Searchable Database: Malaria, reported cases
Feature: "Health, Environment, and Poverty"
