August 5, 2009
Deet May Have Damaging Effects On Nervous System
A study released on Wednesday warned that one of the world's most common insect repellents acts on the central nervous system in the same way as some insecticides and nerve gases, AFP reported.
Researchers say moderate use of the chemical compound deet is most likely safe, but experiments on insects, as well as on enzymes extracted from mice and human neurons, showed for the first time that it can interfere with the proper functioning of the nervous system.
Many experts are urgently calling for further studies to assess deet's potential toxicity to humans, especially when combined with other chemical compounds.
Some suggest the findings may also be linked to the so-called "Gulf War Syndrome," the name given to a complex and variable mix of neurological symptoms reported by tens of thousands of U.S. military veterans who served in the first Gulf War against Iraq in 1990-1991.
Scientists at the U.S. Department of Agriculture developed deet just after World War II, and it has been available as a bug repellent for more than 50 years.
The chemical compound has been used as a barrier against malaria, dengue fever and other mosquito-borne diseases and is sold as lotions, creams and sprays in concentrations from five to 100 percent.
As a precaution, experts advise people to only use enough repellent to cover exposed skin or clothing and caution that repellent should not be applied to cuts, wounds or irritated skin.
The study, published in the British-based open-access journal BMC Biology, said some 200 million people use deet-based products every year.
While it has never exactly been proven how the compound works on blood-seeking insects, it likely blocks the sensory neurons of the flying bugs, or they're simply repelled by the chemical's smell. And there is relatively little research on the effects of deet in humans.
Vincent Corbel, a researcher at the Institute for Development Research in Montpellier, France, and lead author of the study, said it has been used for many years, but there are recent studies now that show a potential toxicity.
He told AFP his team has identified a neurological target for the compound.
Deet interferes with the normal breaking down of acetylcholine (ACh), the most common neurotransmitter in the central nervous system, according to a series of experiments by Corbel and a team of scientists co-led by Bruno Lapied of the University of Angers.
The study found that it does this by blocking the enzyme that normally degrades ACh, acetylcholinesterase, or AChE. The result is a toxic build-up of ACh that ultimately prevents the transmission of signals across the neuron synapse.
Carbamates, a class of insecticides, and the nerve gas sarin, work in the same way, only the effects are stronger and last much longer, which lead the researchers to consider the symptoms noted in victims of Gulf War Syndrome.
A U.S. government report issued last November concluded that many of the pesticides used in the Gulf War, as well as PB and nerve agents, exert toxic effects on the brain and nervous system by altering levels of ACh.
PB, or pyridostigmine bromide, was widely used to protect against nerve gas exposure.
The report, titled "Gulf War Illness and the Health of Gulf War Veterans," points to earlier evidence that overexposure to deet may be toxic for the nervous system.
However, it fails to recognize its potential role as a booster for the more potent chemicals to which soldiers had been exposed.
Corbel said U.S. soldiers wore a cocktail of high doses of PB and insect repellents to protect against mosquito bites, which may have caused symptoms, as both act on the central nervous system in the same way.
But experts say deet is "reversible," meaning its impact is short-lived.
Corbel said further studies would seek to determine at what concentration it might become dangerous to people, especially small children and pregnant women.
"These findings question the safety of deet, particularly in combination with other chemicals, and they highlight the importance of a multidisciplinary approach to the development of safer insect repellents for use in public health," he concluded.
On the Net: