May 28, 2008

Better Mosquito Repellants on the Horizon

Researchers funded by the Defense Department have discovered seven possible replacements for the mosquito repellant DEET (N,N-diethyl-meta-toluamide), the current standard bearer. The work is now moving into a testing phase to ensure the next generation repellants, which work up to several times longer than DEET, aren't harmful. 

DEET was originally developed in 1946 for military use, and became registered for civilian use in 1957.   While DEET's safety record is good, many dislike its odor and some have safety concerns for some use on certain individuals, particularly children and pregnant women.

According to the Environmental Protection Agency (EPA), DEET has been implicated in seizures among children, although there is insufficient information to confirm DEET as the underlying cause. The agency estimates that up to one-third of the U.S. population uses products containing DEET every year to repel biting insects such as ticks and mosquitoes that can spread diseases such as malaria, Lyme disease, encephalitis, Rocky Mountain spotted fever and dengue Fever.

Although commercial availability is still likely years away, preliminary tests on the new repellants conducted on cloth showed promising results, with some chemicals repelling mosquitoes up to 73 days and many working for 40 to 50 days. Compared to the average 17.5 days with DEET, this is a significant improvement.

Many of the new repellants "were just phenomenal," said Ulrich R. Bernier, a research chemist at the Agriculture Department's mosquito and fly research unit, in an Associated Press interview. 

"I was so surprised."

Bernier, who co-authored a report about the study, said he routinely receives new repellants from people, but they usually don't work.

In the current study, researchers wanted to determine what makes repellants work, and then harness that information to discover better ways to chase away disease-carrying insects, Bernier explained.

"We thought, can we do a better job of designing repellants?" he said in a telephone interview with the Associated Press.

The researchers, led by Alan R. Katritzky of the University of Florida, used data obtained from the USDA on hundreds of chemicals collected over 50 years. The chemicals were then rated from "1" to "5" on their ability to repel insects. The team then concentrated on the qualities the most effective ones - the 5s - had in common.

Focusing on a class of chemicals known as N-acylpiperidines, the researchers narrowed the research down to 34 molecules, 23 of which had never been tested, according to Bernier.

Next, the 10 most effective out of the 34 were narrowed down to seven, based on toxicity and production costs. Then tests were conducted on cloth treated with the chemicals and placed on the arms of volunteers.

Bernier said safety tests on the seven chemicals will begin this summer to determine if they are safe to use directly on skin.

Although the military is funding the research, the outcome is expected to benefit the general public as well.

The study was published in Tuesday's edition of Proceedings of the National Academy of Sciences.  

An abstract can be viewed at http://www.pnas.org/cgi/content/abstract/105/21/7359.