Repellent DEET wins hands down for mosquitoes.

Byline: THE HEALTH FILES by Tim Christie The Register-Guard

Until West Nile virus arrived in the United States in 1999, it was easy to forget, at least in this part of the world, that mosquitoes aren't just pesky bugs that annoy anglers and backpackers.

In fact, they're infamous spreaders of death and pestilence around the globe, transmitting disease to more than 700 million people each year, according to the New England Journal of Medicine. The Latin root of the word pest - pestis - means plague, after all.

As West Nile virus continues its steady march across the United States - it's expected to reach Oregon this summer - the need to protect yourself takes on new urgency.

But sorting through the myriad insect repellents on the market can be confusing. Many now boast natural or plant-based ingredients such as citronella. Can they go toe-to-toe with DEET, the long-standing king of mosquito fighters?

For the moment, at least, the answer is no, though a new contender still under study, catnip oil, may yet surpass DEET as the reigning repellent.

A study conducted last year by researchers at the University of North Carolina and published in the New England Journal of Medicine confirmed DEET's supremacy.

DEET - chemical name, N,N-diethyl-meta-toluamide - was proven in clinical studies to repel mosquitoes more effectively and for longer periods than products with plant-based ingredients.

They compared repellents with DEET against plant-based repellents such as those with citronella, soybean oil or eucalyptus oil. Volunteers applied the repellents to their forearms and placed them in mosquito cages, then waited for the first bite as a measure of effectiveness.

The DEET products remained effective for two hours to five hours, depending on the concentration.

OFF! Deep Woods, with 23.8 percent DEET, lasted longest: about five hours.

The researchers didn't test even stronger formulations, such as REI's Jungle Juice, which is 95 percent DEET. But earlier studies have shown the duration of DEET's effectiveness plateaus at concentrations of about 50 percent.

The longest-lasting non-DEET product was Bug Blocker for Kids, which uses soybean oil as its active ingredient. It lasted about an hour and a half.

Citronella-based products, such as Natrapel, Green Ban for People and Buzz Away, lasted anywhere from 13 minutes to 20 minutes.

Skin-So-Soft Bath Oil, which holds urban legend status has a mosquito repellent, lasted just 10 minutes.

In situations where protection from disease-carrying mosquitoes is critical, DEET-based repellents "remain the gold standard of protection," said Dr. Mark Fradin, the UNC dermatologist who led the research.

DEET was developed by the U.S. Army in 1946 and has been used around the world since 1957.

Despite concerns about its toxicity and potential adverse reactions, the UNC researchers said the chemical has "a remarkable safety profile."

After 8 billion human applications over 40 years, fewer than 50 cases of serious toxic effects have been documented, and three-quarters of those were resolved without lingering problems, the researchers concluded.

Many of the cases of toxic effects resulted from long-term, heavy, frequent or whole-body applications of DEET.

Matt Symonds, a salesman in the camping department at the Eugene REI store, is a DEET believer, though he's tried some alternative, homespun methods as well.

"I believe in trade-offs," he said. "Trading off a little bit of toxicity is better than getting yourself bit to death by mosquitoes."

If people are camping in an area with relatively few mosquitoes, they might make themselves naturally repellent by eating brewers yeast capsules, vitamin B1 or raw garlic, Symonds said. When he used to backpack in the Olympic Mountains, he would cut up garlic into little chunks and put them in a film canister and eat them like pills throughout the day.

"It's my take that people who use natural alternatives and find them effective are already naturally repellent," Symonds said.

The UNC researchers, however, cited earlier studies that found no ingested compound, such as garlic or vitamin B1, was capable of repelling mosquitoes.

Scientists are studying why some people are more attractive to mosquitoes than others. Fragrances from soaps, shampoos and deodorants may either repel or attract mosquitoes.

Dark-colored clothing generates more heat, making a person more attractive. But only the mosquito knows for sure.

On the horizon is a substance that's shown great promise as a repellent: catnip oil.

Entomologists at Iowa State University created a stir two years ago when they reported their laboratory tests with the active ingredient in catnip oil was 10 times more effective than DEET in repelling mosquitoes.

"It's at least as good and in some ways better," said Joel Coats, a professor of entomology and toxicology who has led ISU's research into catnip oil.

Catnip oil evaporates more easily than DEET, which may repel mosquitoes through the air, he said.

But that volatility means it doesn't last very long.

"In head-to-head comparisons, I'm fairly sure DEET would last longer on people's skin and clothing," he said.

Catnip, a member of the mint family, has low toxicity, which means it should be safe for children who need short-term protection from mosquitoes, he said.

He cautioned that pure catnip oil is too strong to put directly on the skin.

His lab tested it at concentrations from 1 percent to 5 percent.

The university has since patented the primary active ingredient in catnip oil, nepetalactone, and its research foundation is working with unnamed companies to do human trials so it can be licensed by the U.S. Environmental Protection Agency.

Coats predicted a catnip oil-based repellent will be licensed and on the market in a year or so.

Tim Christie can be reached at 338-2572 or [e-mail].