Sunday, June 25, 2006

West Nile in the DC Area

Researchers are studying the effects of the West Nile Virus on local bird populations and how the virus gets transmitted to humans. To do so, they have been setting up insect traps in certain parks around the Washington and Baltimore metro area to catch mosquitos. Birds at the same sites are being caught for blood tests. The results are interesting:

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.

It has been understood from the beginning that this is primarily a bird disease. Crow populations in certain areas have been devastated by the virus. Other birds have taken a hit as well. What I find perplexing is the migration explanation. Sure, robins do migrate, but their local numbers stay high at least through mid-October because the local migratory population is being replaced by robins travelling south from farther north. While the cause for the spike could probably use further explanation, I see no reason to doubt that the late-summer spike is real. So that should be extra reason to be careful about mosquito bites in late summer: do not keep standing water around your house; use insect repellent on bare skin or keep skin covered. (See this CDC advice on avoiding bites.)

Whatever you do, do not blame the birds! The mosquitos that carry the disease were most likely brought to North America on a very man-made airplane. You can only get West Nile from a mosquito bite, not from contact with an infected bird.

As an aside, the article mentions the following sites as "hot spots" for the West Nile Virus and for testing of birds:

Foggy Bottom near the Watergate Hotel is one of a number of urban hotspots for mosquitoes carrying West Nile virus -- and for Americanrobins. 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 inBaltimore near Orioles Park at Camden Yards.

I am not sure that any of those sites qualifies as a "local bird paradise," as the title of the article suggests. Most of these are very compact areas with little space for breeding or foraging, and they are places that most birds avoid for that reason.

Read the original article in PLoS Biology.