Mosquito-Borne Disease and Climate Change: Should you use DEET?

Mosquito and ticks carry a variety of infectious agents, including those that cause malaria, West Nile, Dengue Fever and Lyme disease. NRDC recently launched a new website with climate maps of the United States. One of the maps shows the areas where two key mosquito species are known and projected to live. These two species are the ones that can carry Dengue fever. Dengue (also known as "Breakbone Fever") causes a characteristic triad of high fever, horrible body aches, and a rash. Last year, there was an outbreak in Florida, and there are frequent small outbreaks along the Texas border. Now is the time of year for clinicians in the Southern U.S. To start being alert to possible cases of this disease. Cases are now required to be reported to the Centers for Disease Control and Prevention.

Check out the NRDC Climate Maps, to see if you live in an area that may be vulnerable to Dengue fever - or to any of the other climate-related health threats highlighted on the site. Meanwhile, here are some things you can do:

• Wear long-sleeved protective clothing and long pants, especially at dawn or dusk;
• Limit outdoor time during dawn and dusk;
• Make sure you have window screens on all your windows, and that they don't have holes;
• Use insect repellants judiciously to help prevent mosquito bites and thus prevent disease.

Which mosquito repellent should you use?

DEET (N,N-diethyl-meta-toluamide) is the active ingredient in many brands of insect repellants sold in the United States. First approved for public use in 1957, DEET has remained the gold-standard as a topical insect repellant and is available in a variety of formulations including, but not limited to, lotions, gels, sprays, foams, and towelettes designed to be applied directly to the skin or clothing.  

Although there is no controversy regarding the efficacy of DEET for preventing insect bites, there have been several case reports associating DEET with seizures in children. One study reviewing alleged DEET- induced encephalopathy and seizures via skin application of DEET in children concluded that repellents containing DEET were not safe and should be avoiding in the young. A very recent study done by an international group of researchers found that DEET inhibits cholinesterase activity, an enzyme necessary for appropriate nervous system function in insects and mammals. Symptoms of cholinesterase inhibition include headache, nausea, convulsion, and in extreme cases, death.

Despite the above, it’s important to note that with proper use, the overall safety record of DEET over the past 50 years has been excellent. There have been 43 reported cases of DEET toxicity, including 17 allergic and cutaneous reactions, 25 with central nervous system symptoms and one case with cardiovascular symptoms. Six deaths have been reported in the setting of DEET, three of them caused by intentional ingestion, one involved a child with a baseline metabolic disorder and two children had reported central nervous system symptoms that occurred after DEET use. 

One review that looked at DEET toxicities reported to poison control centers over a four year period concluded that the risk of DEET toxicity was overall low, reported in 0.05-0.1% of users.  The American Academy of Pediatrics Committee on Environmental Health recommend DEET use only in children over two months of age, at concentrations limited to 10-30 percent.

Alternatives:

Concerns regarding the toxicity of DEET, especially in pediatric populations have led to the discovery and development of other types of insect repellants. Several alternatives to DEET now exist, the most common of them being Picaridin, Permethrin, and Oil of lemon eucalyptus. The US Centers of Disease Control and Prevention has approved the use of Picaridin and oil of lemon eucalyptus as alternatives to DEET with repellent activity sufficient enough to deter mosquitoes. Permethrin is a pesticide with toxicity that seems to be more significant than DEET, so it should be avoided when possible. Some people can develop allergic reactions or rashes to lemon-eucalyptus oil, and it doesn't repel insects for as long as DEET does.

Overall, if you do need an insect repellent, I'd suggest going either with a low-concentration formulation of DEET (30 percent or less) or with picaridin. Avoid any products that mix sunscreen with DEET, since sunscreen needs to be reapplied frequently to be effective, and is mostly necessary in the middle of the day, whereas DEET does not need to be reapplied very frequently, and it's mostly needed in the mornings and evenings when mosquitoes are most active, so a combined formula makes little practical sense.

I'm a believer in avoiding any unnecessary use of chemicals, but insect repellents have an important role in our world, especially as the climate changes and diseases such as West Nile, Lyme, and even Dengue fever spread into new zones.

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