Tigers burning bright

September 16, 2002

FIFTEEN YEARS ago, mosquitoes were not a problem in Baltimore or its suburbs, and West Nile fever was unheard of. Today we have both.

It's a lesson, if we needed one, that borders don't count for much, and that there's little defense against the natural scourges of the rest of the world. Central Maryland this summer is rife with Asian tiger mosquitoes, introduced here in the 1980s and flourishing like gangbusters, and not coincidentally it is also the state's hot zone for West Nile, now in just its third year of American habitation.

Both, unfortunately, are here to stay.

In one sense, the tiger mosquito is the real problem. Unlike most mosquitoes, it defies drought. The tiger happily lays its eggs in any little puddle or container of standing water that it can find. A saucer under a flower pot, a kid's toy left out in the back yard, a roof gutter that doesn't quite fully drain, an old tire -- anything with a little still water in it will do. That's why tiger mosquitoes love cities and suburbs so much; they're the rats of the insect world, and they thrive on human carelessness.

Tigers have another bad habit -- they bite all day long. There's none of this wait-until-dusk business. Also, they're equally happy drawing blood from birds, squirrels, horses, dogs, cats or humans.

And they're carriers of the West Nile virus (along with some native mosquito species). In some parts of the country, including this one, they have to be considered prime suspects -- though hardly the only ones -- in the continuing outbreak.

As of Friday, Maryland had had five confirmed human cases of West Nile fever. In 108 of the state's ZIP codes -- primarily in the city and Baltimore, Howard, Anne Arundel, Montgomery, Prince George's and Frederick counties -- health authorities have stopped testing dead birds because there's no point in confirming the obvious. The virus is abundant in each of them.

Nationally, 54 people have died this summer from West Nile. Nearly 1,300 people have had confirmed cases; perhaps 100 times that number have had the virus but were unaware of it. Organ transplantation can spread the disease, and researchers believe that blood transfusions can as well.

For the moment, doctors don't see a big risk in continuing with those procedures, because their benefits far outweigh the dangers of what is often a very mild disease.

But there's a disturbing note: Large numbers of birds of prey have been dying in the Midwest, and some fear that the virus there may have evolved into a more virulent form -- more virulent for birds, that is. Such transformations in a virus are not uncommon, and that's why health officials in this country need to be particularly vigilant.

In a few years there will likely be a vaccine, but for now the best defense is to attack the mosquitoes -- interlopers and natives alike -- that spread West Nile. That means a spraying campaign where communities and state officials agree it is warranted; but the most effective action would be for each of us to look for standing water in our back yards. Tip it out, and dry it up.

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