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On the Trail of the West Nile Virus

Some scientists race to develop vaccines against the scourge while others probe the possible lingering effects of the mosquito-borne infection.

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If, as most experts agree, West Nile has become established in North America, it may be a disaster for birds and other wildlife. Veterinarians at zoos in Los Angeles and San Diego were so alarmed by the threat of West Nile that they have used an experimental West Nile virus vaccine to protect their California condors. Zoo officials nationwide are deeply concerned about the virus. “We work really hard to be the ‘ark,’ ” said Travis of the Lincoln Park Zoo, “and this has the potential to blow through that.”

 

The future of human West Nile virus disease is trickier to assess. One possibility is that West Nile will follow the pattern of the St. Louis encephalitis virus, which causes only about two dozen cases of encephalitis annually. Scientists still don’t understand precisely why St. Louis encephalitis broke out in 1975 and has since faded. “We don’t know what West Nile is going to do in the future,” the CDC’s Roy Campbell said. “The best indicator is to look at what SLE has done. But in fact we are making a big leap of faith in saying it’s going to be like SLE.”

 

Some experts are unwilling to make that leap, including Anthony Marfin, a medical epidemiologist at the CDC’s Fort Collins branch. He sees parallels between West Nile virus and Japanese encephalitis virus, which causes between 30,000 and 50,000 cases of human encephalitis each year worldwide, but he said there wasn’t enough information yet to predict whether West Nile would become as common. Still, he speculated that eventually U.S. cases of West Nile disease may number in the hundreds each year, “with periodic explosions of thousands of cases.”

 

Federal, state and local officials began gearing up for the 2003 mosquito season as early as this past February. The city of Chicago started eliminating mosquito breeding sites and treating catch basins with insecticide this past May. “We can’t control the weather,” conceded city health official William Paul. “We can’t control bird migration patterns. What we can control is standing water in the urban environment.”

 

Still, the ability of health workers to detect arthropodborne disease has been seriously degraded over the past quarter-century. Since 1983, two National Academy of Sciences reports have warned of a looming shortage of medical entomologists and a steady decline of the infrastructure for surveillance of foreign pathogens. Both predictions have come true, according to Durland Fish, an entomologist at YaleUniversity. “We were better prepared to deal with this 30 years ago than we are now,” said Fish, who is developing satellite maps to analyze West Nile’s spread. “We don’t know how to predict human risk with this disease. We don’t know how to measure [its spread]. And even if we could, what would we do? We’d spray, and that’s a response that’s 50 years old!”

 

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