DDT and Malaria The March 2003 issue of The Washington Monthly contains an interesting article by Alexander Gourevitch entitled "Better Living Through Chemistry." Alas, it is not available online, but it's worth tracking down the print version. The article makes a compelling case that controlled spraying of DDT in Africa could greatly reduce the number of cases of malaria,. which currently number in the hundreds of thousands. Unfortunatly, certain environmental groups are standing in the way of implementing such controlled sprayings.
The usefulness of DDT as an insecticide was discovered in 1939 by Paul Muller, who later won a Nobel Prize in medicine for his trouble. Extensive spraying of DDT in the two decades after WWII led to dramatic decreases in diseases, especially malaria, spread by mosquitoes and lice. The World Health Organization estimates that the number of lives saved as a result number in the millions. However, after many years of spraying some harmful side effects were discovered. Once it enters an ecosystem, DDT remains for a very long time. Eventually it builds up in substantial concentrations in animals, especially fish. It was also discovered to be a carcinogen in large doses. The last straw was when it was found that mosquitoes had developed a resistance to it (a fine example of evolution in action). These effects led the United States to ban the chemical in the early seventies.
Gourevitch points out that extenisve research since then has shown that DDT is harmful only in large doses. There is no evidence linking small quantities of DDT to harmful effects in humans. Furthermore, DDT remains effective as a repellant even in mosquitoes that have developed a resistance to it. There is no other known insecticide that can make that claim. Considering that malaria kills hundreds of thousands of years, which certainly makes it a known health risk, a sensible program of controlled spraying seems entirely reasonable.