Mosquitoes Are Most Deadly
Animal Known To Humans

By Seth Borenstein
Knight Ridder Newspapers

DeLAND, Fla. - - Jonathan Day suspends a live chicken below a tree as bait to try to catch the creature that has killed more humans than any other animal. He gloats: "They don't stand a chance."
They are mosquitoes.
Despite his bravado, Day, a top mosquito scientist, knows that in man's long war against them, the little bloodsuckers usually prevail. Mosquitoes kill more humans worldwide in five minutes than sharks do in a year.
Insect-borne diseases have ravaged America and the world time and again for centuries. In decades past, America all but vanquished mosquito-borne malaria, dengue and yellow fever from its territory - but mosquitoes always come back with another disease. Four different encephalitis viruses have struck thousands of Americans in the past 20 years. Now comes a deadly U.S. epidemic of West Nile virus.
West Nile virus was an African disease until 1999, but since then it has spread across much of America, infecting 156 people and killing nine this summer alone. It won't peak until the first week of September. Officials at the Centers for Disease Control and Prevention estimated Thursday that the epidemic could count about 1,000 cases and 100 deaths by the end of this year.
As alarming and dangerous as West Nile is, scientists like Day say that the ultimate threat to public health is not the disease of the moment - it is instead the delivery system, the eternal, unconquerable mosquito. Like the cockroach, they say the mosquito probably would survive nuclear war.
After a few optimistic years when governments talked of "mosquito eradication," experts now readily admit that mosquitoes are so pervasive and so hardy - they develop resistance to everything man throws at them - that scientists now hope simply to not be overwhelmed. History argues that mosquitoes may be tamped down temporarily, their threat contained for a time, but the bugs always come back.
Deadly mosquito-borne epidemics have swept across America many times before. The most recent previous one was in 1975, when St. Louis Encephalitis killed 95 and infected more than 3,000 people.
Those numbers pale next to the millions of Americans who were stricken in the 19th Century with malaria, an often-deadly disease caused when mosquitoes inject a parasite into a person's bloodstream. Malaria may be banished in America, at least for now, but it still stalks the Earth, spread by mosquitoes.
"It's an extremely deadly thing. We're losing 2.7 million people each year, mainly in Africa, as a function of malaria," said Harvard School of Public Health medical entomologist Andrew Spielman. "The war is not winnable. We are simply managing our environment."
Day and other specialists worry that even deadlier Japanese encephalitis, Rift Valley fever and Ross River fever may follow West Nile's path through the United States.
"The one lesson of West Nile is that any virus from any part of the world can get going in a part of the world where it was previously never known," said Day. "And once it gets going there's no stopping it. California is still fertile ground. Texas is still really fertile ground.
No matter where you go in this country, there's a (common) mosquito."
While this year's West Nile epidemic is centered for now in Louisiana, the past triumphs and future hopes of America's annual mosquito battle are grounded in buggy Florida. What follows is a report from the front lines, where scientists waging the battle have modest hopes and much frustration.
Day is a professor at the University of Florida Medical Entomology Lab in Vero Beach, where he predicts future locales of mosquito-borne disease outbreaks, tests the effectiveness of bug repellents and tries to calculate precisely the rate of infections in mosquito populations.
Day, a 50-year-old former marathoner, is well-suited to his work. One of his earliest childhood memories is standing in his back yard while a plane 250 feet overhead sprayed DDT during a 1956 encephalitis outbreak in his native Massachusetts.
Like other mosquito experts, he doesn't itch when mosquitoes bite. People who get bitten a lot develop immunity to the mosquito chemicals, although not to any virus the bugs may carry.
Pressed by growing concern about the rapid spread of West Nile disease, Day and his 9-year-old son, Spencer, interrupted a beach vacation this month to conduct a first-of-its-kind experiment at Hontoon Island State Park, about 45 minutes west of Daytona Beach. Day was trying to find out how many mosquitoes in his area are infected with West Nile.
Day placed a live chicken in a stocking-like bag that forced its feathers down, giving mosquitoes a clearer path to bite the bird. He put the bagged bird into a 5-gallon can equipped with mosquito-trapping funnels. He repeated the process with a second trap. The birds spent prime mosquito-biting sunset and sunrise hours as bait.
The next morning, Day and his son picked up the traps, and kept and counted the mosquitoes in them. Over the next several days, Day tested a week's worth of chickens and 10,000 mosquitoes for West Nile virus. With more than half of the tests finished so far, there's good news: No West Nile.
If just one in 1,000 mosquitoes has West Nile, the virus is likely to spread from birds to humans in that area. Day will have final results around Aug. 26.
Epidemics of mosquito-borne disease often start right after a drought because the dry spell tends to concentrate animals together, permitting disease to spread quickly from bird-to-mosquito-to-bird. But mosquito-borne epidemics then usually peter out in one year, as immunity to the virus builds up in both human and bird populations. They then spread to new places where immunity has not yet developed.
"I think every year we're going to see West Nile transmission for awhile," Day said. "In terms of human epidemic, Chicago is high risk; Texas is high risk for next year, for years to come. Southern Louisiana, at least they should be done."
Using his own arms - and his son Spencer's arms, too - Day has tested consumer mosquito repellents containing the chemical DEET to determine how long the sprays protect people. The more DEET a repellent contains, the longer its protection will last. For people spending two-and-a-half hours outside, 7 percent DEET will do fine, he said. Many bug repellents, especially those marketed as child-friendly, contain about 7 percent DEET.
While Day studies mosquitoes, John Plate just tries to kill them.
A mosquito technician for Indian River County Mosquito Control, Plate sprays insecticide from his truck at dusk. As he putters by the trailer homes and swamps of Vero Beach, Plate says this fight is personal: In Vietnam, Plate was bitten by more than 2,000 mosquitoes one night and his skin blew up in enormous welts.
"It's nice when you've killed a whole bunch of mosquitoes," Plate says as he spreads a fine mist of the insecticide permethrin and lights up the dusk with a flashing yellow beacon. "I'm happy if we can keep even with them."
Often in the past, the mosquito was the clear winner.
In 1793, yellow fever ravaged Philadelphia, killing 5,500 out of its 55,000 residents. Yellow fever killed 20,000 people in New Orleans and Mississippi in 1853, and another 20,000 there in 1878, when the epidemic ran as far north as Memphis.
During the Civil War, 1.3 million Union soldiers contracted malaria from mosquitoes, and 10,000 of them died - five times as many as were killed at the battle of Antietam, the war's bloodiest battle. (Malaria deaths have not been calculated for Confederate soldiers.)
In the 20th century, America vanquished malaria and yellow fever with a combination of quarantine, medicine, hygiene, and chemical pesticides. DDT made the biggest difference. But the mosquito always returns, often carrying new diseases.
For a short time, experts hoped they had found the answer.
Sixty years ago at a government lab in Orlando, U.S. scientists figured out a way to turn a Swiss-invented moth-killing chemical into the biggest weapon man has ever fielded in the mosquito war: DDT. The legendary pesticide won its inventor a Nobel Prize and saved millions of lives. It was not without flaws, however.
In the summer of 1943, E. John Beidler was a young high school student who helped out around the Army's Orlando-based lab where DDT was being developed.
Beidler and others were standing beside the mosquito-infested Banana River during the first aerial spray tests of the pesticide. It was so buggy that their tan mesh belts initially seemed to be "black fuzzy belts" of swarming mosquitoes.
But within an hour, thanks to the DDT spray, there were "no mosquitoes at all. It was like magic," Beidler said. "All the government agency people thought that this was the answer for insects."
Yet within a decade, experts found that DDT had lost its effectiveness because mosquitoes developed resistance to it. DDT also proved poisonous to all sorts of animals and persisted in the environment, nearly wiping out the bald eagle.
DDT was banned in the U.S. in 1972, but is kept as a malaria-fighter of last resort in Africa and Asia.
Beidler has been mosquito control director in Indian River County since 1955. He knows that victories against mosquitoes are short-lived.
For example, by using an innovative flooding technique to rob salt marsh mosquitoes of their breeding grounds, Beidler was able to reduce the number of the pests found in beach traps from an average of 171 bugs in 1957 to about 2 in 1969.
But a few years later in citrus groves in the county's west end, another kind of mosquito took over - big time. After running tests, officials calculated that 23 tons of adult mosquitoes infested one 560-acre citrus grove. That's about 8 billion mosquitoes.
"If you control 90 percent of the mosquitoes, 10 percent of 8 billion mosquitoes is still a lot of mosquitoes," Day said.
Nevertheless, the fight to contain the mosquito goes on.
To control mosquitoes, experts first try to kill them as worm-like larvae resting in ponds, often using a bacteria that erodes the bug's gut. Larvae are easier to kill than flying adults.
Few pesticides are aimed solely at the adult mosquito. There's not a big market for them because governments aren't spending a lot of money to kill the bugs, said David Brown, president of the American Mosquito Control Association. Overall, AMCA estimates that local governments spend about half a billion dollars a year to fight mosquitoes - slightly less than U.S. consumers spend on fresh doughnuts each year.
"We're down to a few tools," Beidler said.
Some of the best weapons against mosquitoes are environmental and lifestyle changes. The draining of wetlands in the 1950s and 1960s reduced mosquito populations, but as environmental awareness led to expansion of wetlands, the bugs came back.
If you can't eliminate them, at least you can stay away from them, sometimes. The advent of air conditioners, screen doors, and television have helped keep mosquito-borne diseases in check by keeping Americans indoors during prime mosquito-bite hours around dusk and dawn.
Mosquitoes find ways to fight back. The nasty striped Asian Tiger mosquito provides a perfect example.
It came to the United States about 30 years ago in a shipment of used tires and now thrives all over in small puddles of water, such as those found in tires, cans, and gutters. The Asian Tiger is indiscriminate in what it bites, which makes it a good "bridge" mosquito to take diseases from birds to humans.
Asian Tigers are also aggressive in mating. A swarm of mosquitoes mating is a sight to behold, with males massing around the likely bite victim of a female mosquito, waiting for her arrival.
"They just go to the host and hang out and wait for the females to show up," Day said with a chuckle. "It's like a bar."
Once the mosquitoes pair up, watch out. They're prolific. Day keeps photographs of a marsh the size of a football field crowded with wall-to-wall mosquito eggs.
That's why Beidler concedes that his job "is to try to keep it down to a dull roar."
For more information, check out the following Web sites:
The Centers for Disease Control and Prevention's Web page for mosquito-borne viruses:
Harvard University's mosquito-borne disease page:
Florida Medical Entomology Laboratory's Encephalitis Information System, which has updates on the current situation and predictions for mosquito-borne disease:
The American Mosquito Control Association's mosquito information page:
© 2002 Knight Ridder/Tribune Information Services


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