West Nile: On The Move

Even for a disease that moves on wings — of birds and mosquitoes — the West Nile virus is spreading with remarkable speed. Three years after making its first U.S. appearance, in New York, it has spread to 33 other states. This year, after being largely confined to a thick band of East Coast states, the virus has swept rapidly west, reaching as far as South Dakota and Texas. Last week it struck with a vengeance in Louisiana, infecting at least 58 residents and killing four — prompting Governor Mike Foster to declare a statewide emergency.

The westward expansion caught officials from the Centers for Disease Control (CDC) by surprise; they expected the trail of human infections to follow the migratory patterns of birds. Could birds flying south for the winter have strayed off course? Or is the disease — which is transmitted to humans by mosquitoes that have bitten infected birds — being spread by a new breed of mosquito?

Fortunately, the disease is relatively hard to catch. Fewer than 1% of humans who are infected actually get sick, and it does not spread from one person to another. But in a small percentage of cases, particularly those involving the elderly, it can be fatal. The virus causes flulike symptoms within three to 15 days and can lead to a dangerous inflammation of the brain.

The CDC predicts that West Nile will continue its flight westward and eventually spread to every state, except maybe Hawaii and Alaska. Since there is no vaccine or treatment, the best protection is to stay indoors at dawn and dusk, when mosquitoes are most active, and douse exposed skin with insect repellent.