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Battling microscopic monsters

USF wants to test a chemical in homes in hopes of bringing the dust mite to its eight little knees.


© St. Petersburg Times, published July 29, 2000

TAMPA -- It's probably a good thing they're microscopic.

With eight spindly legs, the milky-white body of a maggot, an eyeless, armored head and sharp little pincers, dust mites up close are as gross as any alien menace from science fiction, and just about as hard to eradicate.

They also make millions of Americans sneeze. That's why allergy researchers at the University of South Florida want 120 families to volunteer their homes to help test a chemical designed to kill the mites, which infest pillows, mattresses, sofas and carpets by the millions -- at least.

Homes that qualify must be lousy with dust mites, at least 100 per gram of dust, but that's nothing around here: It's not unusual to find levels of 2,500 per gram of dust in carpets, and up to 10,000 per gram in mattresses, said Dr. Rosa Codina, one of the study's lead researchers and an instructor in the division of allergy and immunology at USF's College of Medicine.

Codina, an animal physiologist who studies allergy-causing critters, hopes to find out whether a boron-based acaricide, which sells as Dustmitex, successfully reduces mite populations.

"We did some preliminary work in the lab, and it works," Codina said. "But we don't know whether or not it's going to work in homes, in real life."

Despite their size -- roughly 100 would fit into the period at the end of this sentence -- dust mites can have a whopping effect on humans. At least a quarter of Americans suffer from allergies, and about a third of those allergies are believed to be triggered or exacerbated by dust mites, experts say. The bugs also have been linked to asthma.

It's not the mites, per se, that cause trouble. Rather it's their waste, and pieces of dead mites that waft into the air.

Dust mites, who are kin to spiders, belong to a group of arachnids that homestead in the nests of birds and mammals, where they feed on the countless skin cells we leave behind. They get water by absorbing it through the air, rather than by drinking it, so they thrive in warm, moist climates and are thickest in the Southeast. Florida is like Nirvana.

"Humans, when they developed housing, developed a nest that's perfect for them to inhabit," said Dr. Larry G. Arlien, professor of biological sciences at Wright State University in Dayton, Ohio, and the country's foremost expert on dust mites.

They're most common in homes with carpet over 2 years old and lots of pets and people, but being a neat-freak doesn't make you immune: Arlien, who has studied dust mites for 30 years and once found 15,000 mites in a mere gram of dust on a recliner, said it's not just dusty homes, or dirty homes that are necessarily prone to having them.

"In our sampling, some of the cleanest homes will have the highest mite densities," he said.

Mites usually live three to six weeks, and they are persistent breeders. The females lay two or three eggs a day, allowing the population to grow by 12 percent to 25 percent a week. The bed is a favorite place.

"We sleep six or seven hours a day. The mattress becomes a micro-environment," Codina explained. "We keep the mattress warm, and mites grow very well."

Until recently, humanity's weapons against them have been about as effective as the club and spear against the woolly mammoth. Conventional bug sprays don't help much. Neither do special air filters. Regular vacuuming has little impact, because mites have sticky feet that can cling to carpet or fabric.

But a few tricks recently have been found to work well, Arlien said. Lowering the humidity can help greatly. Covering pillows and mattresses with plastic or special fabrics helps, too. (Roaches love to eat them, but most folks don't want them around, either.)

USF's Division of Allergy and Immunology began recruiting volunteers for the six-month study this week. Participating homes will be randomly assigned to receive acaricide and weekly vacuuming, a placebo and weekly vacuuming or no treatment whatsoever. All will get mattress and pillow coverings.

Mite populations in each home will be measured at the start of the study, then every two months.

The sponsor of the $200,000 project is the Earth Works, a California company that makes Dustmitex, a boron-based powder that's diluted and sprayed on furniture or carpet.

Boron is a natural substance that's used to kill all sorts of pests, including pine post beetles and roaches. The product has been approved as safe for humans and animals by state regulators in California and Florida and federal regulators, the company says.

James Burnett, president of the Earth Works, said he asked USF to conduct the study because of Codina's extensive experience with the mites. "Going out and actually wrangling the live mites and bringing them back here, it takes a certain expertise," he said. And because of the climate, "Tampa could be the mite capital."

The company hopes the results will bolster sales, and USF hopes to learn more about controlling mites. Codina and her colleagues plan to publish the results in a journal of allergy and immunology, regardless of the findings.

Researchers visited the homes of the first two volunteers this week, but neither quite qualified.

"They had a lot of dead mites," Codina said. "We are looking for live mites."

Dust mite study

Researchers at the USF College of Medicine are seeking 120 single-family homes in Pasco, Hillsborough and Pinellas counties to participate in a study of how well a derivative of a common household chemical, boron, kills dust mites.

Participants will get free mattress and pillow covers, and most will get free weekly vacuuming. For more information, call the USF Division of Allergy and Immunology clinical research unit at (813) 631-4024. Other criteria include:

Homes must have enough mites, at least 100 per gram of dust.

No pregnant or lactating women, or children under 5.

Residents must be in good health. They can have allergies but not asthma.

The homes must have carpet in the living room and bedrooms. It must be more than 2 years old. Sofas must be upholstered with fabric.

Participants may not move from the home for 12 months.

No indoor flea treatment within the six months preceding the start of the study.

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