Beware the birds

July 04, 2000

A deadly new disease is loose in the western hemisphere

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't 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 Health 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.

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. "It had already infected more than half the local geese and sparrows. That's scary."

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's 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'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.

"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. "We think the next outbreak will be along the Gulf coast, where northern migrants remain concentrated," he says.

"It is essential to capture and test healthy local birds to know where West Nile poses a threat," says McLean. "Then mosquito spraying can be targeted to protect people."

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 (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: "Extensive screening of wild birds in hopes of finding the virus would not be cost-effective."
Author: Debora MacKenzie

New Scientist issue: 8th July 2000


New Scientist

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