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- The bird virus that killed seven New Yorkers last year
has now spread all over the Americas, say U.S. researchers. They warn that
the Gulf Coast of the United States will probably see the next outbreak
of West Nile virus.
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- Despite the threat, U.S. authorities have so far failed
to provide the research funding to keep tabs on the virus in wild birds.
The scientists say that scrupulous monitoring of bird populations is needed,
otherwise it won't be possible to identify and spray high-risk areas with
insecticide to kill the mosquitoes that transmit the virus to people.
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- The infection is endemic to Africa, Asia and Europe,
where it resides harmlessly in many bird species but kills others, according
to Bob McLean, head of the National Wildlife Health Center in Madison,
Wis.
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- Humans usually get the disease from mosquito bites when
the population of infected city birds is sufficiently large to infect enough
mosquitoes. In 1997, 527 people in Bucharest, Romania, were ill with West
Nile virus, and 50 died. There is no specific treatment for the infection.
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- The virus may have reached New York last summer in a
bird imported from Israel. However, West Nile expert Zdanek Hubalek of
the Czech Academy of Sciences suggests it may have originally escaped from
the Sloan-Kettering Institute in New York, where in the 1950s a strain
of the virus was given to 95 terminal cancer patients as an experimental
treatment.
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- But there is evidence that the New York outbreak last
summer, which killed thousands of crows and caused encephalitis in 61 New
Yorkers, seven of whom died, resulted from a different strain. But what
is certain, McLean says, is that as early as last summer the virus had
already spread to an alarming extent in the New York area.
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- "It had already infected more than half the local
geese and sparrows. That's scary," McClean says.
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- And the discovery of the virus in birds in New York,
New Jersey and Delaware last month has dashed hopes that it would not survive
the winter. John Rappole and his colleagues at the Smithsonian Institution
Zoo in Front Royal, Va., have calculated that the virus would spread far
and wide from New York if there were susceptible migratory birds congregating
on mosquito-infested wetlands nearby. In this month's issue of Emerging
Infectious Diseases, they and Hubalek report that there are 77 migratory
species there, including ducks, starlings, terns and gulls, capable of
carrying the virus.
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- "The virus is probably in every corner of North
America by now" as well as parts of South America, says Rappole. Another
outbreak could occur anywhere there are enough infected birds, possibly
this summer.
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- "We think the next outbreak will be along the Gulf
Coast, where northern migrants remain concentrated," Rappole says.
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- "It is essential to capture and test healthy local
birds to know where West Nile poses a threat," McLean says. "Then
mosquito spraying can be targeted to protect people."
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- McLean's proposals to screen birds in the coming months
have not yet been funded. Eastern and Gulf states plan to test dead birds
and "sentinel" chickens -- caged birds used as an early warning
system. But this is much less sensitive, McLean warns. Caged chickens are
less likely to encounter infected mosquitoes than free-range birds.
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- But Stephen Ostroff of the Centers for Disease Control
and Prevention in Atlanta told New Scientist: "Extensive screening
of wild birds in hopes of finding the virus would not be cost-effective."
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