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

Research hasn't cut risks posed by ticks, mosquitoes

June 13, 2005|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

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.

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