Meet the Tiger, a Bug With Extra Bite

(Centers for Disease Control and Prevention)
By Maria Scarvalone
Special to The Washington Post
Tuesday, August 19, 2008

When Sydney Williams moved last year from a condo to a house in the Pimmit Hills section of Falls Church, she relished the opportunity to hone her gardening skills in a yard of butterfly bushes, hydrangeas and perennials.

Her first summer of gardening, though, was "an absolute misery," the 43-year-old remembers. "The mosquitoes were awful -- morning, noon and night." And this summer hasn't been any better. "They attacked you so much, you didn't know where they were coming from," says Williams, who wore long sleeves, jeans and socks but still got bitten in places that weren't totally covered even after investing in "gallons" of bug sprays. "I wanted a yard to play in, not a yard to be eaten in," Williams says.

When she realized these mosquitoes were the probable source of the welts and hivelike rashes on her arms and legs, she called the Fairfax County Health Department. Having lived in southern Florida, she was accustomed to mosquito bites, but she had never seen a reaction like that. These mosquitoes, it turned out, were different from those she had encountered before. They were a species relatively new to the area, the Asian tiger mosquito.

Named for its white-striped legs and body, the Asian tiger mosquito, or Aedes albopictus, has been on a global voyage, beginning in Southeast Asia and Japan before winding up in the continental United States in 1985, most likely, experts surmise, via a shipment of used tires. Since then, it has steadily invaded southern and southeastern states. Officials now report its presence in more than 36 states, including Maryland and Virginia, as well as the District.

"It's the most common nuisance mosquito that we have," says Jorge Arias, director of Fairfax County's disease-carrying insects program. Unlike the more well-known Culex mosquito, the Asian tiger breeds in water containers, not swampy marshland, and can therefore thrive around urban and suburban homes, where it lays its eggs in the smallest of puddles formed in plant trays, wheelbarrows, plastic bottle caps and kiddie pools. Also unlike the Culex, it is a persistent daytime feeder, a "voracious, nasty pest," according to Mike Turell, an entomologist with the U.S. Army Medical Research Institute of Infectious Diseases.

What concerns officials is that the mosquito is a potential health risk. The Asian tiger is a known vector not only of West Nile virus, but also of such exotic-sounding diseases as chikungunya fever and dengue, illnesses once a worry only in tropical Africa and Asia.

Dengue, a flulike disease, and its deadly complication, dengue hemorrhagic fever, have no vaccine. Almost eliminated from the Americas in the 1950s, dengue has once again become endemic in many countries south of the United States: Brazil reported more than 200,000 cases in Rio de Janeiro state this year alone. Lately, the disease has made inroads on U.S. territory, with a 2001 epidemic in Hawaii, sporadic appearances along the Texas border with Mexico and outbreaks in Puerto Rico.

"Widespread appearance of dengue in the continental United States is a real possibility," write Anthony Fauci and David Morens of the National Institute of Allergy and Infectious Diseases in the January issue of the Journal of American Medical Association.

These specialists take some comfort, however, in the fact that dengue's primary vector is the Aedes aegypti mosquito rather than the Asian tiger. Some theorize that the Asian tiger might even be of benefit in the fight against dengue because, in areas where it has taken over, Aedes aegypti populations are decreasing. "Paradoxically, the presence of Aedes albopictus may lower the risk of dengue, because it may be out-competing Aedes aegypti," explains Lyle Petersen, director of the Division of Vector-Borne Infectious Diseases at the Centers for Disease Control and Prevention.

Of greater concern to Petersen is chikungunya, which means "that which bends up," because of the stooped posture it can cause. Chikungunya is not fatal, but it causes debilitating fever and joint pain and can leave long-lasting arthritic problems. Discovered in Tanzania in 1953, the disease has spread into India and parts of Southeast Asia. Last August, the first outbreak of chikungunya in continental Europe occurred in Castiglione di Cervia, a small Italian town in Emilia Romagna, an area better known for its Bolognese sauce and beaches than for its bugs.

An Indian residing in Italy had returned from a visit to India feverish with the virus, only to be bitten by a local Asian tiger mosquito, which then spread the flulike disease to more than 200 people in the area.

"I started to feel terrible, really terrible," remembers 63-year-old Antonio Ciani about the illness that hit him suddenly with a 104-degree fever, severe bone pain and headache. "I said goodbye, because I thought I was dying. I couldn't even stand up anymore -- I was like a human larva."

Now that chikungunya is in Italy, health officials are on the alert in the United States. "We know it could certainly cause outbreaks in northern climates," Petersen says.

All you need is one tourist to contract the disease on safari in Africa, return home to the United States and be bitten by an Asian tiger mosquito to begin the transmission cycle, says Petersen, adding that lab tests have identified 56 people with chikungunya who have entered the United States from January 2006 to July 2008. "In some ways, it's a matter of luck -- or bad luck," he explains. "If it happened in Italy, there's no reason it can't happen here."

Local authorities are on the lookout for chikungunya in the Washington area. "This is a hot spot for it, and we have the vector," Arias says. The anti-mosquito material that the Fairfax County Web site offers in response to the threat of West Nile virus would be relevant if there were an outbreak of chikungunya, and the county has mailed brochures to every home. Agencies in Maryland and the District also have mosquito-control programs.

The problem is that getting rid of the pests requires constant vigilance. Pesticide spraying might not reach all the adult mosquitoes hiding underneath backyard shrubbery. "Don't wait until you have adults. That's the end of the line," Arias recommends. The only way to effectively reduce or eliminate the population is to remove the breeding sites: small pools of water that might have collected in plant trays, loose tarps, birdbaths, tires or toys. One of the biggest culprits, he says, is corrugated piping connected to downspouts; the mosquitoes lay eggs inside, where they grow in the water resting in the pipe's grooves.

One saving grace is that the pests do not travel far. "People need to realize that if they have a tiger mosquito problem, the source is very near -- if not their yard, their neighbor's yard," says Mike Cantwell, acting chief of mosquito control at the Maryland Department of Agriculture. They will not travel more than 50 feet unless desperate for a blood meal.

For now, exotic diseases like dengue and chikungunya are more of a concern for health officials looking at future threats than for residents, but the likelihood of new vector-borne illnesses coming to our area is increasing all the time. These diseases "are getting spread around the world by movements of man and goods, by globalization," Petersen says. With more than 500 mosquito-borne viruses out there, "we need a lot more attention for surveillance, mosquito control and research to find the best ways to deal with these problems."

In Falls Church, Sydney Williams is doing her share. She is treating her corrugated drainage pipe with larvicide and spraying her ivy with permethrin, while keeping a watchful eye on her own symptoms. And she's using the literature Fairfax County authorities gave her to enlist her neighbors in the war against the Asian tigers, so she can finally enjoy her garden. "This year, I have my ammo," she says.

Maria Scarvalone is a freelance journalist and avid gardener who has been plagued by Asian tiger mosquitoes at her home in Brooklyn, N.Y. Comments:health@washpost.com.


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