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Tiger mosquitos are here!

Despite a lifespan of only four to six weeks and an inability to fly more than a few hundred yards, the dreaded Asian tiger mosquito (Aedes albopictus) has been reported in 351 counties in 24 states since its August, 1985, discovery in Houston, Tex. Normally, another pesky mosquito messing up summer barbeques would be no big deal. However, the tiger mosquito adds a deadly wrinkle - it can transmit eastern equine encephalitis, a rare, but usually fatal, brain disease. It also is a vector for dengue or breakbone fever, a non-fatal disorder endemic to the tropics and subtropics.

There are 3,600 types of mosquitos throughout the world, indicates Carl J. Mitchell, Chief of Medical Entomology at the National Center for Infectious Diseases, Ft. Collins, Colo. What makes this Asian variety especially dangerous is the insect's habit of living near humans and the fact that it is a very aggressive biter. For instance, Florida's salt marsh mosquito, which carries yellow fever, "tends to hover around your ankles, but the tiger mosquito will come right up in your face. They bite more rapidly, and many people say their bites are more painful," explains Charlie Morris of the University of Florida's Medical Entomology Laboratory.

Mitchell and Morris will be part of a collaborative effort this summer investigating the proliferation of Aedes albopictus in Florida. "Although the tiger mosquito has spread across the country and is found as far north as Minnesota, it is very widespread in Florida; that's where the greatest concentration is found," says Mitchell, pointing out that the potentially deadly insect has invaded 64 of the state's 67 counties.

The tiger mosquito was first introduced in Jacksonville in 1986 and initially moved north, not south, because it thrived in temperate, not hot, climates," Morris reports. "But it is a very adaptable insect. What triggers its hatching is light, not temperature. In the fall, there's less daylight than in summer. This tells the eggs that cold weather is coming and not to hatch. That's why it's proliferating in some of the so-called cold weather states." Eventually, in Florida, the tiger mosquito also moved south, altering its biology so it could breed all year long because there is no real change of seasons.

"This insect requires relatively high humidity in the adult stage," Mitchell points out. "It's no accident that it has not been distributed in arid states or the western half of Texas. It's found in Japan, Korea, and northern China, but also in the tropics and subtropics."

No matter where the tiger mosquito sets up shop, it doesn't discriminate as far as choosing meals. "It feeds on a wide variety of things," says Morris, indicating that bird, deer, and horse blood are equally tasty to this six-legged, millimeter-long invader that can be recognized by a wide white stripe down the middle of its back, white bands on its legs, and white markings on the thorax and abdomen.

The tiger mosquito, which thrives in stagnant water, is believed to have entered the U.S. in 1985 via a shipment of used tires from Japan. Besides multiplying in tire dumps, the insect is at home in tin cans, flower pots, bird-baths, tree holes - anything that contains even a small amount of standing water. "The best way to control this mosquito is to got rid of its breeding sites," Morris notes. "Trouble is, people have a tendency to say, |Oh, why don't you just spray some pesticide and get rid of it that way?' Well, for one thing, Aedes albopictus is a day feeder and lives very closely to people. You can't exactly have a crop dusting plane going through residential neighborhoods in the middle of a summer day. But more important than that is the fact that eliminating its breeding ground of standing water is more effective than any chemical treatment or pesticides."

Perhaps the most fascinating - and most vexing - question is how this mosquito has managed to spread across half the continental U.S. (as well as on every continent except Antarctica) even though it can't fly any more than 500 yards. "It certainly doesn't fly to all these places," says Morris. "Obviously, it's moved around the world by breeding in standing water in various import and export shipments, most likely used tires." Yet, there are other ways to travel. For instance, a single tiger mosquito was found at the Albuquerque, N.M., airport. "The mosquito has moved around Florida the same way people do, in cars and trucks. It also was discovered that they were laying eggs in the plastic vases used in cemeteries. The vases are recycled, and may end up at different cemeteries. So, when the eggs hatch, the mosquito has invaded a new area."

Unlike the malaria epidemic that spread throughout Central and South America at the turn of the century thanks to the mosquito known as Anopheles, Aedes albopictus has not been responsible for any deaths in the U.S., at least not yet. "We're monitoring its populations, and we've isolated four separate viruses that it can carry," says Mitchell. They are eastern equine encephalitis, Potosi, Keystone, and Tensaw. Only the first strain presents an immediate danger. "Eastern equine encephalitis means |inflammation of the brain," Mitchell explains. "It's fairly rare, but severe. About one-third of those infected die, and those that survive likely will have permanent nerve damage. Potosi virus, meanwhile, has not been found to be similar to any other U.S. virus. We're not sure if there's any public health significance to it. Keystone virus has been isolated to mosquitos in Florida, but again, it is not known if it poses a public health danger. Tensaw, too, which has been isolated in Texas, is not known to pose a danger to public health."

"What's needed," concludes Morris, "is an honest and thorough evaluation of the real potential dangers of this mosquito. Before this spring, when we received a grant from the Florida Department of Agriculture, we had neither the funds nor the manpower to go around the state and collect all these types of mosquitos and isolate them for tests. My personal feeling is that there isn't any danger. I think the tiger mosquito just happened to be found in an old tire pile at the same time there was an outbreak of eastern equine encephalitis (in 1991, when 200 horses and five humans contracted the disease; 70% of the horses and two of the people died]. It was the largest outbreak in 10 years, but the following year [1992], things went back to normal: 51 horses and no humans were infected."

Thus far, the Asian tiger mosquito has been spotted in Hawaii, California, New Mexico, Texas, Louisiana, Mississippi, Alabama, Georgia, Florida, North and South Carolina, Tennessee, Arkansas, Oklahoma, Kansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Minnesota, Virginia, Maryland, and Delaware.
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Author:Barrett, Wayne M.
Publication:USA Today (Magazine)
Date:Jun 1, 1993
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