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Researchers Question Severity Of Threat From West Nile Virus

By Robert Lee Hotz
LOS ANGELES TIMES -- The symptoms of West Nile virus are like portents from a vintage Hitchcock film: There is the whine of mosquitoes. Crows fall dead from the sky; horses sicken.

Panic spreads and a tabloid fever grips the land. In Texas, the virus left its calling card for the first time when an infected grackle dropped dead last month near San Antonio. Within days, birds in Oklahoma and South Dakota started dying. This week, horses in Colorado, Wyoming, Montana and New Mexico were stricken.

The virus -- virtually unknown in the Western hemisphere three years ago -- is poised to leap the barrier of the Rocky Mountains into California.

As the largest outbreak yet of West Nile Virus reaches its predicted peak during the next two weeks, medical authorities acknowledge that the disease is spreading more quickly than they expected. The virus has infected birds and mammals, including humans, in 37 states, nearly doubling its known territory this year.

Yet in the grand scheme of disease, West Nile virus may be a bit player.

Most people infected with the virus may never even realize they are ill. A mild infection may confer lifelong immunity, researchers said.

In areas of Africa where the disease is endemic, it is a mild childhood malady that almost never develops serious consequences, said Dr. Lyle Petersen, an infectious disease expert at the U.S. Centers for Disease Control and Prevention in Atlanta.

Indeed, public health officials in New York City, the epicenter of the first U.S. outbreak of West Nile virus in 1999, so far have reported only four cases of the disease this summer, suggesting that people are becoming acclimated to the disease.

As the national immune system adjusts, the virus may fall back into the obscurity of wildlife diseases, several public health experts said.

Just as thousands of tourists visiting the Channel Islands safely coexist with deer mice infected with the deadly hanta virus, so people may learn to live with the low risk of West Nile virus.

Backpackers in 15 states, mostly in the West, routinely risk contact with flea-infested animals harboring the bubonic plague or tularemia without worrying unduly about the handful of human cases reported every year.

If the virus behaves like related diseases such as St. Louis encephalitis and California encephalitis, which also are harbored in birds and transmitted by mosquitoes, it will fade into the sporadic background noise of public health.

Consider St. Louis encephalitis. The St. Louis variety has been common in the Midwest, with 128 cases reported nationally in an average year. It has been almost a generation since the last major human outbreak of the disease.

By that pattern, the next human outbreak of West Nile virus may not be nearly so severe or so widespread, CDC experts said. It could be a decade or more before the next notable outbreak occurs.

In fact, there were no major outbreaks of West Nile virus anywhere in the world between 1975 and the mid-1990s.