With West Nile virus spreading on the wings of migratory birds, health officials around the nation have stepped up their vigilance, in the belief that it is just a matter of time until the disease hits their doorstep.
Since New York first detected it in 1999, West Nile virus has rapidly invaded 35 states and the District of Columbia, extending as far west as Texas and the Dakotas. In Louisiana, at least 85 people have been stricken and seven have died.
"The virus is going to move from coast to coast. I'm very certain of that," says Lyle Peterson, an expert on West Nile virus with the Division of Vector-Borne Infectious Diseases in Fort Collins, Colo. The division, part of the Centers for Disease Control and Prevention in Atlanta, studies diseases that are transmitted by insects. "It is the fastest spread I've seen."
Scientists are jumping on an unparalleled opportunity to study the virus as it moves into new environments. Mosquitoes feed on infected birds, then transmit the virus to humans through bites. And unlike other such viruses, West Nile kills some of the birds it infects, leaving a trail for investigators.
The CDC has dispatched a team of about 20 professionals to Louisiana, including epidemiologists, entomologists and behavioral scientists. Besides helping state officials with the outbreak, they are expanding research to delve deeper into the ways of the virus.
"This is a virus that was never seen in this country before 1999, yet it's already infected 30 different species of mosquitoes and 110 species of birds," says Anthony Marfin, also a CDC West Nile expert.
Questions about the latest outbreak include why the virus seems to have occurred earlier in the year and why it seems to be affecting younger people than in previous outbreaks.
The CDC is also conducting a clinical study of patients who exhibit severe neurological symptoms, to track the symptoms and progression of the diseases and its potential long-term effects. The agency also is searching for cases of West Nile fever, a milder form of the infection. Its victims develop flulike symptoms -- such as headache, body aches and swollen glands. But they don't show the more severe conditions of West Nile virus, such as encephalitis, an inflammation of the brain and its casing that can provoke confusion, paralysis, coma and death. Less than 1% of those infected become seriously ill, with the elderly being at highest risk.
Surveillance teams on the East Coast are tracking the spread of the infection using global positioning satellites. Labs are using sophisticated diagnostic tests to identify the virus. But the West Nile alert programs ultimately depend on teams of people doing "shoe-leather epidemiology" from field workers to doctors in examining rooms.
"No amount of technology will replace a smart physician, who will see symptoms and think of what the possibilities could be before tests are ever ordered," says Jeffrey Duchin, chief of communicable-disease control for Seattle and King County, in Washington. "It's the human element."
California, Oregon and Washington state health workers are pushing surveillance efforts into high gear. Mosquito wrangler Jo Marie Brauner, chasing bugs and larvae for Washington's state health department, ventures forth armed with a hanging "CO2" trap, which attracts mosquitoes by emitting carbon dioxide to simulate the breath of warm-blooded creatures. She also wields a dipper with a telescoping handle for sampling the dark, fetid water alive with wiggling larvae.
The work can get unsavory. At a dump near a horse pasture, where she had to sample from 300,000 waterlogged tires, she says, "We had to crawl on our bellies under barbed wire past the horse [droppings] to the tires."
In the hills east of Berkeley, Calif., Patrick Turney maintains three flocks of red leghorns, sentinel chickens that serve as an early warning system of the disease. As field operations supervisor of Alameda County mosquito abatement, Mr. Turney regularly makes a pinprick in the combs of 21 chickens and deposits a blood drop on to filter paper that is later tested for several kinds of encephalitis. His subjects resent the intrusion. "Today," says Mr. Turney, "a rooster wasn't very happy and tried to peck and claw."
Public health officials are also stepping up efforts to educate physicians on how to spot symptoms of the disease in patients. Washington state had a scare last week, when a traveler consulted a local doctor for fever, rash, aches and a sore throat. Initially treated for strep throat, the man mentioned that he had just visited Louisiana. Suspicious, the doctor ran another test.
"Lo and behold, it was positive," says Jo Hoffman, Washington state communicable-disease epidemiologist. Fortunately, the imported case was mild. Moreover, because humans can't spread the disease, Dr. Hoffman contends, "there's no risk of transmission."
The West Coast is doubly vulnerable to the invasion of potential new carriers who enter through its international seaports. California nurseries unwittingly imported the Asian tiger mosquito in pots of "lucky bamboo." And in Washington, a new species of Asian mosquito never before seen west of the Mississippi stowed away aboard a shipment of old water-filled tires from the Far East to Seattle. Inspectors found its larvae in a nearby abandoned aquarium.
"It's a particularly feisty mosquito," a spokesman says about the species, Ochlerotatus japonicus japonicus. Unlike other mosquitoes that bite at dawn and dusk, japonicus feeds in the daytime, making it tough for people to avoid being bitten. It can carry West Nile virus.
There is no treatment for West Nile virus, and the best prevention is to avoid mosquito bites by draining ponds, wearing protective clothing and using repellents with the insecticide Deet.
If and when West Nile virus hits the West Coast, officials are prepared to pull out the big guns. California mosquito control, now quelling larvae with environmentally compatible hormones and bacteria, would expand to include air and ground spraying with insecticides to kill adult mosquitoes, a state health official said. Washington, Oregon and California would expand their surveillance to the area of infestation. Carol Glaser, acting chief of the viral laboratory of the California state health department, says her office already analyzes suspicious cases of encephalitis, but if an outbreak occurs, "We'll ramp up."
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