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Sunday, May 31, 2015

With Outdoor Activity Season in Full Swing: Insects Can Carry Nasty Diseases

Bugs bite. And when they do, they can make us miserable, itchy, bumpy – and, occasionally, very sick.

With outdoor activity season in full swing, here's what you need to know.

Insects can carry nasty diseases.

Most people who get a few mosquito or tick bites will not get sick. But some mosquitoes and ticks can carry bacteria and viruses that cause serious human illnesses – and some of those illnesses have recently become more common in the United States.

Take West Nile Virus. That mosquito-borne illness came to the United States in 1999. Since then, more than 17,000 cases have been reported, says the federal Centers for Disease Control and Prevention. While typical symptoms include headaches, joint pains and rashes, a few people have serious neurologic symptoms and some die.

A newer threat: chikungunya, another viral disease spread by mosquitoes. In 2014, nearly 2,500 cases were reported on the U.S. mainland, mostly among people bitten while travelling. But 11 people were infected by mosquitoes in Florida. While chikungunya rarely kills, it can cause severe joint pain that lasts for months.

Then there's Lyme disease, caused by a bacteria spread by ticks. The CDC has been tracking that disease since 1991, and says there are about 30,000 reported cases each year, but that the real number is likely ten times bigger.

Your risk depends largely on where you live (or travel).

About 96% of confirmed Lyme cases occur in just 13 states, clustered in the Northeast and Midwest, CDC says.

And the mosquitoes that carry chikungunya are tropical species, meaning only southern areas need to watch for local outbreaks, says Jonathan Day, a professor of medical entomology at the University of Florida. The fact that people in the United States spend so much time inside, with air conditioning and screened windows, may help prevent big outbreaks, he says.

Mosquitoes that can carry West Nile do live throughout the United States. But local conditions determine where epidemics catch fire, Day says. For example, a 2012 outbreak near Dallas was spurred by drought – which caused virus-carrying mosquitoes and birds to cluster around scarce water sources. Another outbreak in Arizona was linked to un-drained swimming pools in foreclosed houses abandoned during the recession, he says.

Some people get bit more than others.

It's true: mosquitoes and ticks find some people especially attractive. Scientists disagree on the reasons.

Day says he is convinced it's mostly about carbon dioxide: mosquitoes and ticks find their victims by detecting it and some of us produce more than others. That includes heavier people, pregnant women and exercisers. "The amount of carbon dioxide you produce depends on your metabolic rate," he says.
But Uli Bernier, a research chemist for the U.S. Department of Agriculture, says he has seen evidence that other factors are at work over many years of exposing people to mosquitoes in his Gainesville, Fla., lab. He's seen different mosquitoes zero in on different people. He's also found that some people (himself included) seem to become more attractive to mosquitoes over time.

What you eat and drink may matter, Day and Bernier agree. Alcohol, in particular, seems to attract mosquitoes, they say. At least one study also suggested smokers were at higher risk – but probably because they spend so much time smoking outside, Day says.

Several repellents work well.

CDC says you want one that includes DEET (N,N-diethyl-meta-toluamide), picaridin, oil of lemon eucalyptus or a chemical called IR3535.

While DEET products have long been thought the most effective, recent tests by Consumer Reports gave the edge to picaridin and oil of lemon eucalyptus.

"It was really a surprise," and should be good news to people uneasy with the possible side effects of DEET, says the magazine's senior health and food editor, Sue Byrne.

DEET has been linked with seizures and other serious side effects, mostly in people who swallowed it or applied heavy concentrations.

When used as directed, it's safe, Bernier says: "It's been around 63 years and has a remarkable safety record."

Other strategies can help.

Wear long sleeves, pants, closed shoes and socks for a walk in the woods. You also can also spray a repellent called permethrin on clothing and gear. And check yourself for ticks when you go inside.

For an evening on your patio, try this: sit next to a fan running at high speed. Consumer Reports found that helped repel mosquitoes, and Day says it makes sense: "Mosquitoes do not have an ability to fly in wind conditions much more than 1 mile an hour."

Here's what doesn't work.

Consumer Reports gave thumbs down to:

"Natural" repellent sprays made with plant oils, such as citronella, lemongrass, and rosemary

Wrist bands containing citronella or geraniol oil

Citronella candles

The American Academy of Pediatrics adds these to the ineffective list:
  • Garlic
  • Vitamin B1 supplements
  • Bug zappers (they may actually attract insects)
  • Ultrasonic devices
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