By Brenda Goodman, MA
WebMD Health News
Reviewed by Hansa D. Bhargava, MD
Feb. 1, 2016 -- They're tiny. They attack with supreme stealth, biting in full daylight with no buzz and no sting. And they carry viruses that can be lethal to their preferred food source: us.
The Aedes aegypti, or yellow fever mosquito, killed more soldiers than guns did during the Spanish-American War. And now these black-and-white striped femme fatales -- only the females suck blood -- are causing misery through Central and South America as they pass the viruses that cause dengue fever, yellow fever, chikungunya and now Zika virus disease from person to person.
Their ancestors lived in the forest where they fed on all manner of warm-blooded creatures, but some time in recent history -- no one is sure exactly when -- the modern Aedes mosquito developed a preference for just one animal -- humans.
"They only live in association with humans. And they have all these physical and behavior adaptations to do it," says Carolyn McBride, PhD. She's an assistant professor of ecology and evolutionary biology at Princeton University who specializes in Aedes aegypti.
"They have an amazing ability to recognize human odor," McBride says. "You can put on a lab glove and cut a little hole in the back so that just an inch of skin is exposed, and they'll find it."
Where They Hide Out
Experts who have spent some time studying Aedes mosquitoes are amazed at how well they've adapted to feeding on people.
Take, for instance, their habitat. They don't have a lot of stamina in the air. Their flight range is just 300 to 600 feet. As a result, insecticidal sprays mostly don't work on this breed, because it's hard to catch them airborne.
To feed, they have to stick close to their intended targets, a.k.a. us. They live under decks, patio furniture, and in homes that don't have cool air -- they don't much like air conditioning. They especially love the drip trays that collect extra water under potted plants. But that's not the only place you'll find them.
They "can breed in incredibly small amounts of water," says Joe Conlon, spokesman for the American Mosquito Control Association.
"When I was in Suriname, South America, several years ago, I saw them breeding very happily in discarded soda bottle caps," he says.
In New Jersey, researchers at Rutgers University found them breeding in water that had pooled in discarded snack-size potato chip bags.
"These mosquitoes are in people's backyards," says Dina Fonseca, PhD, an entomologist and associate professor at Rutgers. They live in containers, she says, and are "urban, domestic mosquitoes."
In 2009, Fonseca and her team went house to house through neighborhoods around Trenton, N.J., trying to understand exactly where these mosquitoes and their close relatives, Aedes albopictus, live and lay their eggs. (In lab experiments, albopictus mosquitoes have also been shown to carry Zika.) They dumped and checked out more than 20,000 different water-holding containers for the study.
They found these mosquitos mainly in buckets, in the drip trays under potted plants, and in little pools of water than collect in the crevices of outdoor equipment like lawn mowers and air conditioners.
Even in the most manicured, clutter-free yards, they found infestations. One place that was a reliable hideout? The corrugated extenders that people attach to downspouts to direct rainwater away from homes.
"Sometimes they are so long that you always have water inside of those accordion folds. We've gotten 500 larvae out of those little folds before," Fonseca says.
And Margaret Chan, MD, director-general of the World Health Organization, warned that many areas could see their number of mosquitoes boom this year because of the El Nino weather pattern -- the strongest in almost two decades. El Nino often brings warmer, wetter winter weather, which allows these insects to hatch earlier and breed longer.
How to Protect Yourself
The Zika virus is spread when a mosquito bites an infected person, then bites an uninfected person and passes the virus. Most infected people don't show symptoms. But the virus is suspected of causing microcephaly in babies of infected pregnant women, although a cause-and-effect link hasn't been definitely established. Microcephaly causes devastating, sometimes-fatal brain damage and can result in miscarriage or stillbirth.
The CDC has warned women who are pregnant or may become pregnant to consider postponing travel to more than 25 countries and territories in Central and South America, and the Caribbean.
In Brazil, the situation is so desperate that they're trying an experiment: releasing genetically engineered male mosquitoes into the wild. When they breed with females, they pass a self-destruct gene to their offspring that causes them to die before they reach adulthood. Oxitec, the British company that produces that mosquito, claims in tests that it cut wild Aedes populations by as much as 90%.
The company says it has been in talks with the FDA to test its mosquitoes in the Florida Keys, but hasn't yet received approval to try it here. Supporters say the Oxitec mosquito could end the menace of Zika and other mosquito-borne viruses without the toxic after-effects of pesticides. But critics worry about the unintended consequences of releasing a genetically modified insect into the wild.
While we wait to see if science can save us, warm, wet weather is on the way.
Fonseca says the first Aedes mosquitoes will hatch in an area after the temperature has been above 50 degrees for at least 16 days.
To protect yourself, experts agree that the most important thing to do is to get rid of standing water in and around your house. But the mosquitoes aren't always where you might think. In her house-to-house survey, Fonseca didn't often find them up high in places like roof gutters or in ornamental ponds or in swimming pools, even when they'd been left untreated and neglected. Instead, she says, think low and small.
Fonseca and Conlon offer these suggestions:
- Empty buckets or watering cans. If you have a rain barrel, treat it with a non-toxic product designed to kill mosquito larvae.
- Drill holes in your trash or recycling bins so they don't collect water.
- Even though it's a pain to disconnect them, unscrew and empty downspout extenders at least once every 5 days. That's how long it takes mosquito eggs to hatch.
- If you've got plants in containers, empty their drip trays at least once a week. Same goes for outdoor-furniture covers that may hold pockets of water after a rainstorm.
- Try to cover any outdoor equipment, like a barbecue grill, so it doesn't collect water in places you can't see or reach.
- Aedes mosquitoes like to bite below the knees, so long pants and socks are important. Wear long sleeves as well.
- Use a mosquito repellent. Conlon says the active ingredients DEET or a slightly less sticky, greasy alternative called picaridin both work well.
Here's another tip from Conlon, who isn't just a professional mosquito fighter, but also a Florida resident who has to deal with them year-round: If you're sitting on a porch or patio, use box fans to create a strong breeze around your feet and legs. Since mosquitoes don't do well in wind, a draft helps set up a mechanical barrier, and it also helps blow away all the human odors that cue them to your warm-blooded presence.
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