Panic Over Virus May Exceed the Threat

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 until 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 anticipated peak in the next two weeks, medical authorities acknowledge that the disease is spreading more quickly than expected. The virus has infected birds and mammals in 41 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 it. So far this year, human cases have been reported in 20 states plus the District of Columbia.

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 hantavirus, so people may learn to live with the low risk of West Nile virus.

Backpackers in California and 14 other states, mostly in the West, routinely risk contact with flea-infested animals harboring the bubonic plague or tularemia without worry. Only a handful of human cases are reported each year.

If the West Nile 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. It 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.

Then it suddenly reappeared in Israel, Romania and Russia. Something about the virus had changed. It infected horses for the first time and caused more severe health consequences when it infected humans.

“There is some evidence to suggest that this is a new and more virulent strain of West Nile virus,” said Duane Gubler, director of vector-borne diseases at the National Center for Infectious Diseases in Fort Collins, Colo.

Preliminary laboratory analysis at the CDC suggests that there are significant genetic differences between the newer strain of West Nile and those found in Africa that may account for its greater virulence.

As a disease of birds, the West Nile virus is far more deadly than the St. Louis virus, said wildlife disease expert Bob McLean at the National Wildlife Research Center in Fort Collins. So far it has infected more than 120 species of birds.

“For birds, we have never seen a virulent virus like this before,” McLean said.

As a newcomer to the United States, the West Nile virus itself may be a symptom of more fundamental ills.

Changes in climate, local ecology, technology and lifestyle have fostered the emergence of 30 serious diseases in recent decades, aided in part by a dangerous indifference to the threat of insect-borne diseases, said Dr. Paul Epstein, associate director of the Center for Health and the Global Environment at the Harvard University Medical School.

“We are seeing new diseases emerge,” Epstein said. “There is a three-ring circus of causes. The carriers of disease are getting boosted by ecological, sociological and climatological disturbances.

“People are rightly concerned,” he added. “The public is reading this correctly as signs of instability.”

Where humankind sees the chaos and uncertainty of modern life, nature sees an opportunity.

The bacterium that causes Legionnaire’s disease, for example, took advantage of the contemporary taste for air conditioning, spreading through modern ventilation systems and cooling towers. AIDS and hepatitis C were helped by innovations in medical care and spread, in part, through unscreened blood transfusions.

A national appetite for fast food created the opportunity for salmonella and other food-borne illnesses to spread quickly through centrally processed foods that are distributed to many states.

But through the sustained vigilance of public health authorities and new medical treatments, most of these diseases have been controlled before they reached epidemic proportions. With the exception of AIDS, the new diseases largely remain background threats, not plagues.

A virus such as West Nile is a fellow traveler of global commerce and tourism, Gubler said.

Several strains of the virus circulate worldwide, but only one has reached the United States so far.

It appears to have originated in the Middle East. No one knows how it got here. But it has moved so quickly since it arrived that it has stirred an unusually high level of fear in a public whose nerves were already on edge this year after rounds of anthrax threats and the specter of biological warfare.

“It has been a quick march across the country,” said John Edman, director of the Center for Vector-Borne Diseases at UC Davis. “The spread westward has been faster than it was last year.”

So far, 371 people have gotten sick. Sixteen have died, officials at the CDC said. There is no cure or effective treatment.

In response, federal public health officials this week poured an additional $4 million into the Southeastern states hardest hit, bringing to $31 million the amount of federal emergency money directed at the disease this summer.

Such insect-borne diseases are likely to grow in importance as international travel becomes easier and human populations move into new areas, UC Davis entomologist Tom Scott said.

In Louisiana, where almost half of this year’s cases have been reported, growing suburban development along swamplands may have exposed people to infected mosquitoes, said tropical medicine expert Dr. Susan McLellan at Tulane University.

“We have a greater risk of what used to be wildlife diseases,” McLean said.

Wildlife experts said Southern California can expect to see the West Nile virus within a year as migrating birds carrying the infection up the Pacific flyway from Mexico.

All in all, it is a familiar American story of public health, in which an exotic virus finds a second chance in the New World.

“West Nile virus has been brought to fertile ground in a new hemisphere,” said McLellan at Tulane.

“It is a huge mistake to think the United States can escape the medical consequences of being part of a larger world.”