[at-l] CAUTION URGED USING INSECT REPELLENTS CONTAINING DEET

[wdaniels@bestweb.net (Walter Daniels)]

CAUTION URGED USING INSECT REPELLENTS CONTAINING DEET

Date: 020501
From: http://www.ascribe.org/

AScribe Newswire, May 1, 2002

DUKE UNIVERSITY PHARMACOLOGIST SAYS ANIMAL STUDIES ON EFFECTS ON BRAIN
OF INSECTICIDE DEET WARRANT FURTHER TESTING AND CAUTION IN HUMAN USE

 Durham, NC - A Duke University Medical Center pharmacologist is
recommending caution when using the insecticide DEET, after his animal
studies last year found the chemical causes diffuse brain cell death
and behavioral changes in rats after frequent and prolonged use.

 Mohamed Abou-Donia, Ph.D. has also called for further government
testing of the chemical's safety in short-term and occasional use,
especially in view of Health Canada's recent decision to ban products
with more than 30 percent of the chemical. Every year, approximately
one-third of the U.S. population uses insect repellents containing
DEET, available in more than 230 products with concentrations up to
100 percent.

 While the chemical's risks to humans are still being intensely
debated, Abou-Donia says his 30 years of research on pesticides' brain
effects clearly indicate the need for caution among the general
public.

 His numerous studies in rats, two of them published last year,
clearly demonstrate that frequent and prolonged applications of DEET
cause neurons to die in regions of the brain that control muscle
movement, learning, memory and concentration. Moreover, rats treated
with an average human dose of DEET (40 mg/kg body weight) performed
far worse than control rats when challenged with physical tasks
requiring muscle control, strength and coordination. Such effects are
consistent with physical symptoms in humans reported in the medical
literature, especially by Persian Gulf War veterans, said Abou-Donia.

 "If used sparingly, infrequently and by itself, DEET may not have
negative effects - the literature here isn't clear," he said. "But
frequent and heavy use of DEET, especially in combination with other
chemicals or medications, could cause brain deficits in vulnerable
populations."

 Children in particular are at risk for subtle brain changes caused by
chemicals in the environment, because their skin more readily absorbs
them, and chemicals more potently affect their developing nervous
systems, said Abou-Donia. Commonly used preparations like
insecticide-based lice-killing shampoos and insect repellents are
assumed to be safe because severe consequences are rare in the medical
literature. Yet subtle symptoms - such as muscle weakness, fatigue or
memory lapses --might be attributed erroneously to other causes, he
said.

 With heavy exposure to DEET and other insecticides, humans may
experience memory loss, headache, weakness, fatigue, muscle and joint
pain, tremors and shortness of breath, said Abou-Donia. His earlier
research, examining the brain effects of three chemicals used during
the Persian Gulf War, clearly demonstrated that chickens exhibited
similar signs that the Gulf War veterans complained of upon returning
from service. (Journal of Toxicology and Experimental Health, May,
1996, Volume 48, p. 35 - 56).

 Such overt symptoms are not seen immediately after use but may
manifest themselves months or years after exposure, making a
cause-and-effect relationship difficult to establish , said
Abou-Donia. By studying animals such as chickens and rats, however,
researchers are able to compress the time between exposure and the
onset of symptoms: 10 months of a rat's life is several years in a
human's life. Moreover, researchers can study layers of the rats'
brains at various stages after exposure to measure the chemical's
effects on the brain.

 Indeed, Abou-Donia's two most recent studies demonstrate the severe
brain and behavioral deficits that rats experience after two months of
daily skin applications with DEET and permethrin, another common
insecticide, (Experimental Neurology, 2001, volume 172 , p.153- 171);
and following 60 days of exposure to DEET and permethrin, and 15 days
of pyridostigmine bromide, an anti-nerve gas agent (Journal of
Toxicology and Environmental Health, 2001, volume 64, p. 373-384).
Both studies examined the effects of each drug alone and in
combination.

 In each study, the treated animals initially appeared to be normal,
just like the control group, said Abou-Donia. But when challenged with
neurobehavioral tasks that required muscle control, strength and
coordination, the rats demonstrated serious impairments. Moreover, a
detailed analysis of their brains clearly showed that large numbers of
brain cells were dying within three critical brain structures: the
cerebral cortex, which controls muscles and movement; the hippocampal
formation, which controls memory, learning and concentration; and the
cerebellum, which synchronizes body movements.

 In addition, many of the surviving brain cells showed signs of
degeneration and damage consistent with the presence of harmful
byproducts called oxygen free radicals (also known as reactive oxygen
species), which can damage DNA and cell membranes in the brain and the
nervous system.

 The most severe brain cell changes and sensorimotor deficits were
seen among rats exposed to combinations of DEET, permethrin and the
anti-nerve gas agent pyridostigmine bromide, which reduces the body's
normal ability to inactivate pesticides. Such findings confirmed
Abou-Donia's 1996 and 2001 animal studies demonstrating that harmless
doses of these three chemicals proved highly toxic to the brain and
nervous system when used in combination.

 "The take home message is to be safe and cautious when using
insecticides," said Abou-Donia. "Never use insect repellents on
infants, and be wary of using them on children in general. Never
combine insecticides with each other or use them with other
medications. Even so simple a drug as an antihistamine could interact
with DEET to cause toxic side effects. Don't spray your yard for bugs
and then take medications. Until we have more data on potential
interactions in humans, safe is better than sorry."

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