THE bird virus that killed seven New Yorkers last year has now spread all
over the Americas, say US researchers. They warn that the Gulf coast of the US
will probably see the next outbreak of West Nile virus.
Despite the threat, authorities in the US 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鈥檛 be
possible to identify and spray high-risk areas with insecticide to kill the
mosquitoes that transmit the virus to people.
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 91色情片 Center in Madison, Wisconsin. 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. But there is evidence
that the New York outbreak last summer which killed thousands of crows, and
caused encephalitis in 61 New Yorkers, 7 of whom died, resulted from a different
strain.
But what is certain, says McLean, is that as early as last summer the virus
had already spread to an alarming extent in the New York area. 鈥淚t had already
infected more than half the local geese and sparrows. That鈥檚 scary.鈥�
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鈥檚 zoo in Front
Royal, Virginia, 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鈥檚 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.
鈥淭he virus is probably in every corner of North America by now鈥� as well as
parts of South America, says Rappole. Another outbreak could occur anywhere
there are enough infected birds, possibly this summer. 鈥淲e think the next
outbreak will be along the Gulf coast, where northern migrants remain
concentrated,鈥� he says.
鈥淚t is essential to capture and test healthy local birds to know where West
Nile poses a threat,鈥� says McLean. 鈥淭hen mosquito spraying can be targeted to
protect people.鈥�
McLean鈥檚 proposals to screen birds in the coming months have not yet been
funded. Eastern and Gulf states plan to test dead birds and 鈥渟entinel鈥�
chickens鈥攃aged birds used as an early warning system
(New Scientist, 20 May, p 7).
But this is much less sensitive, warns McLean. Caged chickens are less likely
to encounter infected mosquitoes than free-range birds.
But Stephen Ostroff of the Centers for Disease Control and Prevention in
Atlanta told New Scientist: 鈥淓xtensive screening of wild birds in hopes
of finding the virus would not be cost-effective.鈥�
