Lather on that protection; mosquitoes of different types potentially bring different woes

SACRAMENTO — Admit it: Heading outside in summer, you grab sunscreen, sunglasses, maybe even a hat, but often leave behind bug repellent — assuming you have any around.

In the age of West Nile virus, public-health messages urging everyone to wear repellent have become as common as reminders to wear sunscreen.

Doing it is another matter.

Fewer than half of Americans wear repellent regularly, and residents of the West are the biggest laggards, with only 23 percent believed to be consistent users, according to surveys for the U.S. Centers for Disease Control and Prevention.

Mostly, people simply forget, or don’t think it’s important, said Emily Zielinski-Gutierrez, a behavioral scientist at CDC.

“The biggest issue is people not feeling they’re at risk for mosquitoes bites. Like, those who say: ‘I don’t get bitten,’” Zielinski-Gutierrez said.

Because of West Nile virus, which showed up in New York in 1999 and has now spread coast to coast, public-health specialists are pushing repellent as a potentially life-saving habit.

Spread by the bite of infected mosquitoes, West Nile virus sickens only about 20 percent of those it infects, but it has the power to disable and kill.

Moreover, scientists don’t know who is susceptible. People over 50 and those with weak immune systems appear to be most vulnerable, but young, seemingly robust people have succumbed, too.

With 935 cases and 19 fatalities, California led the nation in West Nile cases last year. No cases have been reported this year to date, but infected mosquitoes have been found in Los Angeles and Riverside counties.

Zielinski-Gutierrez has no illusions of persuading everyone to wear repellent, but she would like to see 65 to 70 percent of Americans — especially age 50 and up — apply repellent habitually.

Confusion about what to use, when and how is an issue.

“We get a lot of questions,” said Jennifer Benito, a spokeswoman for the Sacramento-Yolo Mosquito and Vector Control District.

How long does the repellent last? What’s the difference between 7 percent concentration and 25 percent concentration? How does it work? Why does CDC recommend certain types of repellent?

Manufacturers offer a welter of products containing a variety of active ingredients, from herbal blends to concoctions with intimidating chemical names.

The CDC’s list of recommended repellents is short: DEET, oil of lemon eucalyptus and picaridin.

The endorsements are based upon studies that have shown these agents stay potent for hours at a time. That doesn’t mean other repellents don’t work, but they haven’t been proven reliably effective for long.

“They may repel for 20 to 30 minutes, but after that, they break down, or they provide some repellency but not enough to be effective in preventing disease transmission,” said Chester Moore, a research entomologist recently retired from the CDC now teaching at Colorado State University.

“You’re really looking for around 100 percent (protection against bites) if you’re talking about disease transmission,” Moore said.

Still, Moore acknowledged, a repellent that works only briefly may be suitable for someone who is outdoors for less than an hour.

He also noted that no one really knows how any repellent works.

Such details tend to get lost in short public-health messages. From the view of researchers who study bug repellents, the field is filled with ifs and buts.

For example, individuals vary in their attractiveness to mosquitoes. By the same token, repellents vary in effectiveness against different mosquito species.

Not only that, the same species of mosquito may react differently to a repellent depending on the environment, said Donald Barnard, a research entomologist at the U.S. Department of Agriculture Center for Medical, Agricultural and Veterinary Entomology in Gainesville.

“I’m in north-central Florida. If I drive down to Miami, the very same species of mosquitoes here may have different feeding patterns and host preferences there,” Barnard said.

Developed 60 years ago by the U.S. Army for military use, DEET has become the gold standard in repellents because it works against a variety of biting bugs and stands up for hours on end.

The higher the percentage of DEET, the longer-lasting the formulation — up to a point. Barnard said concentrations above 40 percent confer no more repellency, and most people need no more than 30 percent.

A problem with DEET is that it has a reputation — undeserved, government officials say — for being dangerous. Since 1960, 46 people have reported having seizures after being exposed to DEET, according to the U.S. Environmental Protection Agency.

In a review of DEET in 1998, the EPA could not determine whether the seizures were directly related to the repellent. In approving DEET for continued use, the EPA required manufacturers to print uniform cautions, such as not applying on the hands or near the eyes and mouth of young children, and directions to wash off the repellent when returning indoors.

Another hitch with DEET is that it dissolves plastics, so it can ruin things such as watch crystals and synthetic fabrics.

Whatever the repellent, Barnard said it’s important to heed label directions and warnings.

Scott Carroll, an insect behaviorist and co-founder of Carroll Loye Biological Research consulting company in Davis, has tested oil of lemon eucalyptus in Butte County, Calif.

Carroll said he was pleased to find that oil of lemon eucalyptus works so well, given some people’s misgivings about DEET. He’d like manufacturers to continue developing more and better options.

“Hopefully in the near future, we would come up with something that is really nice to use and lasts half a day,” Carroll said, “(something) that you would use like a deodorant or like brushing your teeth.”

It’s not only protection against West Nile virus that he has in mind. “There’s a reasonable chance that global climate change will affect those of us in the northern latitudes by bringing more insect-borne diseases,” he said.