Mosquitoes That Carry Malaria, Other Diseases Avoid Homes Sprayed With DDT, Study Says
The pesticide DDT physically repels mosquitoes that transmit malaria and other diseases, and spraying the pesticide indoors reduces the risk of disease transmission by almost three-quarters, according to a study recently published in PLoS One, Reuters reports. Donald Roberts of the Uniformed Services University of the Health Sciences in Bethesda, Maryland, and colleagues tested how the Aedes aegypti mosquito -- which does not transmit malaria but can carry dengue and yellow fever -- in Thailand responded to the use of DDT. In huts sprayed with the pesticide, 59 of 100 mosquitoes used in the study did not enter. Of the 41 that did enter, two died, and only 27 mosquitoes could theoretically bite and survive, according to the researchers. They said that during a 24-hour period, DDT reduced the risk of a mosquito bite by 73%. Although the mosquito studied does not transmit malaria, researchers said the effect likely is the same for the Anopheles mosquito, which does transmit the disease. "The historical record of malaria control operations show that DDT is the most cost-effective chemical for malaria control," the researchers wrote, adding that "[e]ven now, DDT is still considered to be the cheapest and most effective chemical for use in house spray operations."
Two other chemicals -- alphacypermethrin and dieldrin -- also were found to be effective, but not to the same degree as DDT, according to the study. The researchers found that alphacypermethrin did not prevent any mosquitoes from entering huts and that it killed 15 mosquitoes. The chemical also caused 46 mosquitoes to exit the hut prematurely, nine of which died -- translating to 61% effectiveness -- according to the study. Dieldrin also did not prevent mosquitoes from entering huts, but only eight mosquitoes survived long enough to be able to bite, the researchers said. They added that mosquitoes likely could develop resistance to dieldrin (Reuters, 8/9).
The study is available online.
