People can prevent mosquito bites by staying inside at the prime mosquito-biting times of dawn and dusk, by wearing long pants and long sleeves, and by using mosquito repellent. DEET has been in use worldwide as an insect repellent since 1946. "This substance has a remarkable safety profile," according to Mark Fradin of the University of North Carolina, in a 1998 paper on insect repellent safety. "Twenty years of empirical testing of more than 20,000 other compounds has not resulted in another marketed chemical product with the duration of protection and broad- spectrum effectiveness of DEET," he wrote.
For a 2002 research paper in the New England Journal of Medicine, 15 volunteers applied various mosquito repellents to their arms, stuck their arms in cages with hungry mosquitoes, and timed how long it took for the first bite. A product containing 24 percent DEET protected volunteers' arms for an average of five hours. A 5 percent DEET product gave one to two hours of protection. In other studies, DEET effectiveness leveled off above 50 percent concentration.
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More About West Nile Virus
- The King County number for all West Nile virus concerns, including dead-bird reports: 206-205-4394
- Recorded information: 206-205-3883
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Two plant-based products were as effective as 5 percent DEET. A soybean oil product called Bite Blocker, marketed by HOMS, protected from bites for one and a half to two hours. Repel and Fite Bite, two brand names for a eucalyptus oil formula, caused a rash in one subject but gave bite protection of one to three hours. The nationally marketed citronella products tested in this study only gave about 20 minutes protection. In other studies, some citronella products that are only marketed locally or regionally scored about two hours of bite protection. Wristbands impregnated with various mosquito repellents gave no protection beyond two inches from the wristband.
No mosquito repellent is completely free of side effects. None should be used around the eyes, and any of these products will cause rashes in a few individuals. The American Academy of Pediatrics recommends using no stronger than 10 percent DEET on children.
Even a mild West Nile virus infection results in immunity, and younger people are more likely to have milder infections. Seattleites who consider themselves young might be tempted to let the mosquitoes bite them while they're young enough to fight the virus. Warns Jeff Duchin, chief of Communicable Disease Control, Epidemiology and Immunization Programs at Public Health-Seattle & King County: "We really can't advise people to intentionally get infected. A small proportion, even of young, healthy people, get very sick. Some never fully recover neurologically. Are you going to be one of the lucky ones? DEET is really very safe."
There is no vaccine approved for humans, as there is for horses, but drug companies are working on it.
NEIGHBORHOOD DANGERS
Mosquitoes lay eggs in standing water as little as a Dixie cup left on the deck or as large as a pond. "People don't realize how small a volume of standing water can serve as a breeding site," says Saito, the wildlife veterinarian at the USGS National Wildlife Health Center. "Even a bottle cap."
Mosquitoes begin as sesame-seed-sized eggs laid in water. They hatch in the water into tiny wiggly worms called larvae, as long as a dime is thick. They molt into winged adult mosquitoes. Only adult female mosquitoes bite.
An essential step in controlling mosquitoes is making water unavailable to them. People can protect themselves and others by eliminating standing water around their homes and businesses. Water should be emptied twice a week from birdbaths, flower-pot saucers, kiddie pools, old tires, wheelbarrows, gutters, or anywhere that it collects.
As the disease swept across the country last year, public-health personnel got panicked calls from citizens. King County has produced a 25-minute educational video available for loan to groups. It is also in streaming video on the county's Web site, at www.metrokc.gov/health/westnile/. "Our basic message is habitat reduction and personal protection," says Moore of the county health department.
Preventing infection with West Nile virus means depending on the home and yard maintenance of other people. That confounds traditional frontier notions of privacy and private property.
"People call up and complain about their neighbors" leaving water in mosquito-breeding containers, says Everett's Mathias. "I tell them, don't get too confrontational about this." At a public meeting in Everett in March, concerned citizens thought owners of ponds on private property should be required to larvicide them. "We don't think we have the legal authority to do that, and we probably wouldn't use it even if we thought we did," says Mathias. King County has "no authority to require anyone to do anything" about neglected standing water, says Karasz-Dominguez.
"One neglected pool could really contribute to a focal outbreak [of disease] in a neighborhood," says Turner from Oregon. "You're putting your neighbors at risk."
Merilee D. Karr is a University of Washington- trained physician and freelance writer who lives in Portland.
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