Oh, the perils of vacationing in mosquito territory. These little bloodsuckers have made a meal of me around the globe, and I’ve longed for a definitive guide to repelling them. What really works? When and where are extra precautions necessary?
I turned to scientists who study mosquito behavior to find out. They took a break from investigating neurons and odor receptors to offer travel advice.
“Mosquitoes are able to seek out a human being like a guided missile,” said Anandasankar Ray, a scientist at the University of California, Riverside.
It helps to know your enemy in order to conquer her (yes, her — only female mosquitoes bite).
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As it turns out, you play a part in her raison d’être. She bites you, Ray explained, because she requires material from your blood to produce her eggs. Imagine a mosquito flitting about when suddenly she encounters a little cloud of carbon dioxide. This plume is one of many coming out of your mouth as you lounge poolside in Rio. Special sensors allow the mosquito to detect the plume, a sign that a living vertebrate is near.
As she draws close to the source, her sensors pick up odors emitted from your skin. These odors, many of which are produced by bacteria in your skin, help the mosquito determine that you’re not a horse or a dog but a human — her favorite meal. She homes in on you, possibly aided by infrared radiation coming off your warm body.
“Almost like in the Predator movies,” Ray said.
But back to you and your needs.
To protect yourself, you must know where and when the mosquitoes that carry debilitating diseases — malaria, filariasis, yellow fever, dengue — bite.
“If you’re in Central America, South America, Southeast Asia, Vietnam, Thailand, Malaysia — all of these places that are the most beautiful travel destinations, it’s really a concern,” said Leslie B. Vosshall, a scientist at Rockefeller University in New York.
Dengue and yellow fever are primarily spread by Aedes aegypti, mosquitoes that live in tropical and subtropical areas —though they are increasingly found in urban areas — including Africa, Asia, North America, the Caribbean and Latin America. This species bites during the day. Feeding typically spikes a couple of hours after sunrise and late afternoon, Ray said.
Each year about 50 million to 100 million people get dengue fever, a viral infection that often requires hospitalization and can develop into deadly hemorrhagic fever, according to the World Health Organization. There is no vaccine and no cure. Bed nets, Ray said, are a must.
Aedes aegypti can also transmit the chikungunya virus, which causes fever and joint pain. Chikungunya has hit Asia, Africa, India, Europe and the Americas (and into the eastern Caribbean this winter), according to the WHO. While there is no cure, most patients recover.
Another species, Culex, may carry lymphatic filariasis, an infection that can result in elephantiasis. Places most at risk include Bangladesh, Democratic Republic of Congo, Ethiopia, India, Indonesia, Myanmar, Nigeria, Nepal, Philippines and the United Republic of Tanzania. Culex mosquitoes can also carry West Nile virus, found in Africa, Europe, the Middle East, North America and West Asia. These mosquitoes prefer birds but will bite humans, too.
“They will try and descend on you while sleeping,” Ray said. Use a bed net.
Anopheles gambiae, mosquitoes that can spread malaria, often bite at dusk and late at night, Ray said. The WHO says travelers are at risk of malaria infection in 99 countries, mostly in Africa, Asia and the Americas. Yet unlike dengue and chikungunya, malaria can be prevented, even treated, with medication.
What Works, What Doesn’t
“The gold standard of insect repellency continues to be DEET,” Ray said. Developed by the Army in 1946, DEET is a chemical that can melt your nail polish. That said, the Environmental Protection Agency does not consider it to be a health concern if it is used infrequently and properly.
DEET is sold in concentrations from less than 5 percent to 100 percent. Wearing long sleeves and pants will reduce the amount you need to use. Still, covering up is not foolproof. “If they’re very desperate,” Vosshall said, mosquitoes will “bite through jeans.”
An alternative is Avon Skin So Soft with picaridin, a synthetic version of piperine, the active component of black pepper.
What about natural botanical repellents that rely on plant extracts?
“It smells better and it doesn’t melt your sunglasses,” Vosshall said. But “the scientific evidence that those things work is weak to nonexistent.”
Certain unconventional techniques can help, like taking showers (mosquitoes are drawn to sweat that has been on your skin for a while, Ray said) and, for reasons that remain unclear, avoiding alcohol.
“When people drink alcohol they become attractive to mosquitoes,” he said.
There are also spatial repellents, which you should buy if you are vacationing in a country with mosquito-borne diseases and your accommodations do not have window screens. The safest of these repellents release a low amount of insecticide, like ThermaCELL lanterns, which use butane cartridges to heat mats saturated with repellent that then rises into the air. The effect of long-term exposure, however, is not clear.
Citronella candles and oils “work somewhat,” he said. So does having someone around whom mosquitoes find irresistible.
“Many different groups have tested this idea that some people are more attractive than others and it’s absolutely true,” Vosshall said. “But we don’t exactly know why.”