Archive for Sunday, August 18, 2002

Mosquito deadliest animal on Earth

West Nile just one of many diseases spread by insect

August 18, 2002


— 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 11 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.

Deadlier concerns

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.

Mosquito expertise

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 were 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 next week.

"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."

Mosquito hunting

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.

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