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From back yard to bloodstream: The summer bug battle is rejoined

THE BALTIMORE SUN

You don't have to read the headlines to know that they're nasty creatures. And the news is still bad for those who venture outdoors this summer: We're a long way from wiping out the 60 species of mosquito that cause West Nile virus and the deer tick that carries Lyme disease.

And despite research involving garlic, catnip, eucalyptus and volunteers willing to stand in tubs full of ticks, there is no infallible system for keeping the bugs out of your back yard -- and your bloodstream.

"There's a tremendous push being made to see if we can find something. But there's not many chemicals out there as candidates," said Jerome A. Klun, an entomologist with the U.S. Department of Agriculture's research lab in Beltsville.

Beltsville researchers have been awarded $4 million in Defense Department grants to come up with repellents to protect troops from ticks and mosquitoes that transmit malaria, dengue and yellow fever overseas.

To that end, Klun and colleague John Carroll will create their own version of Fear Factor this fall when they and other volunteers douse their ankles in three kinds of repellent and step into plastic tubs filled with 100 lab-raised ticks each -- to see how many ticks ignore the repellent and crawl up their legs.

The experiment will run for six days as the researchers compare SS-220, a repellent developed by Klun and other Beltsville researchers not yet on the market, with Picaridin, a commercially available repellent, and a solution containing the popular insect repellent chemical known as DEET.

Carroll, 59, said there's no danger that the ticks are carrying Lyme disease. Not only are they lab-raised, they're also lone star ticks, a different variety from the deer ticks that transmit the disease.

Nor does the tub of ticks give him the creeps. "When I'm out in the field, it's more risky than if I'm standing in a tub and I can see what's going on," he said.

For Carroll and other bug fighters, part of the problem in finding a perfect repellent is the complexity of the bugs.

The pests have 30 million years of evolution on their side, and they've developed sensors that zero in on the carbon dioxide and other chemicals we emit. Once they sense us, they use different approaches to get into our bloodstreams.

The female mosquito -- the one that bites -- approaches like a Stealth fighter, and once it lands, a probe-like cutting apparatus in her head finds our blood, which provides protein to nourish her eggs.

Meanwhile, the wingless tick waits in the brush -- sometimes for days -- to snatch a ride on a leg, arm, head or neck.

Males and females dig their mouths into our skin, and they can stay attached for days, sometimes leaving poison picked up from other animals as they siphon blood.

Despite years of effort, scientists aren't sure what in our sweat and breath attracts the insects, and what best drives them off.

"We don't fully understand what the human cues are," Klun said.

Preliminary evidence confirms what many suspect -- that some will be eaten alive by mosquitoes while others nearby remain un-nibbled. Ethane, ethanol, acetone and isoprene -- chemicals found in varying amounts in sweat and exhaled breath -- might attract mosquitoes, studies show.

Some researchers are convinced that chemical changes in our sweat, often caused by our diets, play a key role.

Testing garlic

Dr. Thiruchandurai V. Rajan, chief of pathology at the University of Connecticut Health Center, was inspired to check out the effects of garlic on repelling mosquitoes because a colleague's wife was feeding garlic to her horse. He learned that it's a common practice throughout the United States to feed garlic to horses and dogs to prevent mosquito bites.

In his experiment, dozens of human test subjects took garlic capsules or placebos and then inserted arms into a mosquito cage to see whether it had any effect on the number of bites they received.

It didn't.

Rajan suspects that a longer experiment in which subjects eat more garlic for longer periods might show some improvement. The question is whether eating so much garlic would be more effective at driving away insects or friends.

"You may be repelling mosquitoes, but the question is, is it worth it socially?" he said. Meanwhile, health officials remain concerned about the tick's ability to spread Lyme disease and the mosquito's West Nile virus.

West Nile virus, discovered in Uganda in 1937, infected 2,535 people in the United States last year and killed 98, according to the Centers for Disease Control and Prevention. The virus has caused 260 U.S. deaths and infected 10,000 people since its arrival was documented in 1999.

In Maryland, there were 16 West Nile cases last year and no fatalities, said Kim Mitchell, an epidemiologist with the state health department's Center for Veterinary Public Health.

Lyme disease, so named in 1975 because it was first reported in Lyme, Conn., can cause heart trouble, fainting spells, vision problems and arthritis if left untreated.

There were 17,000 U.S. cases last year, including 891 in Maryland, according to Mitchell and CDC reports. Officials say those numbers could increase in the coming years.

Mitchell said the number of Maryland Lyme disease cases fluctuates between 600 and 900 annually.

Booming market

Concern about pest-borne disease has spawned an explosion in the market for mosquito traps, zappers, foggers, ultraviolet lights, repellents and sprays. Repellents alone generate about $100 million a year in sales, according to the market research firm ACNielsen.

"We've seen tremendous growth," said Gordon Jones, a vice president of Biophysics Corp., a Rhode Island company that sells mosquito traps for $295 to $1,195.

The traps get rid of mosquitos by converting propane to carbon dioxide, enticing them into a trap, where they are killed. Running 24 hours a day, a trap will rid up to 1 1/4 acres of mosquitoes in 30 days, Jones said. In 2003, Consumer Reports found that the traps were effective, but its researchers recommended less expensive approaches first, such as repellents and protective clothing.

One problem is that so many people just don't like repellent. Only 30 percent of the people who venture outdoors ever wear the stuff, surveys show.

"They don't like the way it smells, or they don't like the way it feels on their skin," said Brian Weekley, president of Minnesota-based Bugg Products.

Weekley, a chemical engineer, left the cosmetics industry 11 years ago to create an insect repellent with what he says is exactly the right blend of vanilla fragrance and the popular, proven bug repellent known as DEET. Still, it's a hard sell.

"People are very skeptical about the repellent industry because there's so much folklore and junk out there," Weekley said.

Catnip extract

Joel Coats, an Iowa State University entomologist, said it was folklore that attracted him to an oil extracted from catnip, a mintlike herb named for its intoxicating effect on felines. Coats is convinced that the oil is one of several botanical products that can repel mosquitoes and could one day be a replacement for DEET.

Although most studies indicate DEET is safe, some experts recommend it only in low doses. They point to evidence that high doses may cause health problems, particularly when it's combined with other medications or insecticides.

In high concentrations, DEET is also a plasticizer -- if applied to the skin, it will soften plastic surfaces touched by those wearing it.

In 2001, Coats inserted groups of 20 mosquitoes into a glass tube and found that they consistently avoided portions of the surface treated with the oil. The university has since patented a synthetic compound made from the catnip oil.

"If you use DEET in low concentrations, it's not so bad. But we think there's just as good, if not better, repellents out there," he said.

At Beltsville, much of the research is aimed at coming up with a replacement for DEET, the common name for N,N-diethyl-meta-toluamide.

It was developed in the 1950s and is a key ingredient in repellents and insecticide sprays worldwide.

"Finding a replacement for DEET is probably the holy grail in the field right now," said Murray Isman, an entomologist at the University of British Columbia in Vancouver.

Still, DEET remains the gold standard for keeping away mosquitoes and ticks, and most experts say repellents laced with 20 percent to 30 percent DEET are safe.

"It's the only thing worthwhile on the market. None of the others do as well, and none of the others have the safety record," said Nancy Breisch, an urban entomologist with the University of Maryland.

Minimizing the risks

To minimize the risk of West Nile virus, Lyme disease and other bug-borne ailments, experts recommend these steps:

Remove rainwater from tires or other debris. Chlorinate pools properly; drain birdbaths and wading pools once a week. Water is mosquito breeding ground.

Keep gutters clear of debris.

If practical, consider using a fan if you're outdoors in one spot. Even a low setting will help. A steady breeze discourages mosquitoes.

Keep grass cut short and trim foliage where practical. Ticks like tall grass and shady foliage with no breezes.

When hiking, stick to trails. Ticks hide in shrubs.

Consider using a repellent with DEET. Many experienced campers and hikers also treat gear and clothing with permethrin, a contact insecticide.

If you need sunscreen, apply the sunscreen first and wait 20 minutes for your skin to absorb it before applying repellent.

If you spend much time outdoors, wear long-sleeved shirts, pants and other protective clothing, and check yourself once a day for ticks, in the shower if convenient.

To remove a tick, use tweezers and grasp it as close to your skin as possible, pulling it out slowly. Cleanse the area with antiseptic. It takes more than a day for ticks to transmit Lyme disease, so prompt removal minimizes the risk.

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