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Clues on West Nile Sought at Local Bird Paradises

A robin, captured in a researcher's mist net, is the favorite source of blood for the mosquitoes that carry West Nile virus. When robins finish breeding and move out late in the summer, mosquitoes increasingly target humans.
A robin, captured in a researcher's mist net, is the favorite source of blood for the mosquitoes that carry West Nile virus. When robins finish breeding and move out late in the summer, mosquitoes increasingly target humans. (By Gerald Martineau - The Washington Post)

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By Cheryl Lyn Dybas
Special to The Washington Post
Monday, June 26, 2006

Dawn mist settled onto trees and bushes in the dog park on 26th Street NW, obscuring signs for Canal Road and the Whitehurst Freeway. The drizzle hid the antics of American robins chasing wormy early-morning meals. It also cloaked a threat more menacing than the fogged-in rush hour: mosquitoes carrying West Nile virus.

Robins foraging in seemingly tranquil places such as the park often pay a steep price: a bite from a mosquito laden with the lethal virus.

Foggy Bottom near the Watergate Hotel is one of a number of urban hot spots for mosquitoes carrying West Nile virus -- and for American robins. Other hot spots include the areas around the Hirshhorn Museum, the National Gallery of Art and the National Museum of Natural History. Not to mention Bethesda and Ridgeley's Delight, a posh neighborhood in Baltimore near Orioles Park at Camden Yards.

"We'd like to find out why these locations are hot," said biologist Peter Daszak of the Consortium for Conservation Medicine in New York, "and what we can do to decrease the impact of the virus on wildlife and humans." As they search for answers, scientists from the consortium are conducting studies on the links between changes in the environment and threats to wildlife and human health.

From May through September -- "picnic season," Daszak calls it -- infectious-disease ecologist Marm Kilpatrick and a team of biologists catch robins and other birds in fine-mesh nets strung between upright poles and snare mosquitoes in insect traps hung from tree limbs. The traps are baited with "stinky water" -- bits of grass, rabbit food and yeast mixed in water and left in a sealed jug in the sun for a week: mosquito manna.

"It's CSI: Infectious Diseases," said David Winograd, a neighbor passing by who paused to watch the research team's work.

Kilpatrick, who is with the consortium, collects thousands of mosquitoes at hot spots and samples those that have just fed. He sequences the DNA in their blood meals to identify the bird species the mosquitoes bit and takes blood samples from robins and other birds to test them for West Nile virus.

Robins, it turns out, appear to be taking the hit for humans, getting sick and dying as did thousands of crows that were infected in the first wave of West Nile virus after it arrived in North America. Thanks to the robins, humans who frequent the 26th Street dog park and similar areas have a lower chance of contracting the virus, at least in spring and early summer months. The reason? To mosquitoes, robins are far more tempting meals.

Then the scene changes.

"Robins begin to migrate south in late July and August," Kilpatrick said, "leaving mosquitoes on the hunt for blood from another source."

That source turns out to be Homo sapiens . The number of human infections with the virus shoots up come the dog days of August. Then it's mosquito vs. man or woman, instead of mosquito vs. robin.

Since it arrived in the United States in 1999, West Nile virus has become the major "vector-borne" disease here, with 826 reported deaths, 22,000 illnesses and "almost certainly a million people infected," Daszak said. Recent data suggest that the virus will cause 2,000 to 10,000 new U.S. cases a year, according to consortium reports.


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