Thursday, February 3, 2011

DDT and Genetic Resistance

DDT is a chlorine-containing synthesized chemical that was first recognized as a pesticide in 1939. In 1955, the World Health Organization began a program to eradicate malaria worldwide, relying heavily on DDT. It was also used throughout the 1940s and 1950s to help control typhus, a disease caused by the bacteria Rickettsia. Both of these diseases were nearly wiped out in certain countries, but it was less effective in tropical regions and the application was not always permanent. Spraying programs were abandoned due to many concerns; one of the most widely studied was the eggshell-thinning effect it had on many birds of prey, including the bald eagle and the peregrine falcon. DDT also became a major concern when certain insects, including mosquitoes, began showing resistance to the chemical. More shockingly, recent studies have shown that insects that developed resistance to DDT gained additional genetic advantages over their rivals. For example, a study by the University of Bath showed that resistant fruit flies produce offspring that are more likely to thrive even once spraying has been abandoned. This is thought to be caused by females passing on an advantage associated with the metabolic enzyme cytochrome P450, which becomes over-expressed once exposure to DDT occurs. This is similar to how antibiotic resistance may potentially confer the same kind of genetic advantage to ‘superbug’ bacteria. Based on this knowledge, I think it is pertinent that scientists consider the effect that insecticides, herbicides, and antibiotics may have on a population before they are used. Resistant organisms may one day completely replace non-resistant organisms if large scale dispersion of chemical agents are used. In conclusion, although the World Health Organization estimates that approximately 25 million human lives have been saved by DDT use, a question of whether the ends justify the means comes into play, and must be carefully weighed in these situations.


http://www.sciencemag.org/content/297/5590/2253.full

http://www.scienceinafrica.co.za/2005/july/ddtinsects.htm

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