Bird flu knocks on Europe’s door

Chief veterinary officials from the European Union’s 25 member states met in Brussels on Thursday to discuss what to do if wild birds carrying H5N1 bird flu bring it to Europe from Russia. But they concluded it is not clear whether wild birds are spreading the virus in Russia, nor how likely it is that birds migrating into Europe could be carrying it.

H5N1 bird flu has been identified in backyard poultry in the Novosibirsk region of Russia, where an outbreak started in late July. DNA sequence information from samples near Novosibirsk shows it is highly similar to the virus that killed thousands of wild birds at Qinghai Lake in China in May 2005. Russia has also reported outbreaks involving H5 bird flu in backyard poultry in its Altai Kray, Tyuman, Omsk, Kurgan and Cheyabinsk regions, which cover a band of territory parallel to the northern border of Kazakhstan.
H5N1 flu has also been confirmed in Kazakhstan. It is not clear how similar any of these latter viruses are to the Qinghai H5N1 or others that have circulated in east Asia and caused 57 human deaths so far.

But whether this spread is likely to continue into Europe depends on whether it is being carried by healthy migrating birds. If instead the virus is being spread by trade in infected poultry, as it has been in south-east Asia, the picture would be different. And the infections reported so far do coincide geographically with major rail, trade and travel links through the region. Evidence for spread by wild birds is circumstantial. Yevgeny Nepoklonov, head of the veterinary department of the Russian Agriculture Ministry, told the World Animal Health Organisation (OIE) in Paris this month that in the six territories where outbreaks have been reported, “the first [domestic] birds to be affected are those kept in homes close to reservoirs” – where wild birds may visit.

On the other hand, not one healthy wild bird carrying highly pathogenic H5N1 has yet been reported, apart from a few carrying a somewhat different virus in Hong Kong in 2002. Hon Ip, a virologist at the US National Wildlife Health Center in Madison, Wisconsin, US, notes that in Russia’s report on Novosibirsk to the OIE, the H5N1 virus it had isolated from a wild duck was different from the viruses isolated in its domestic poultry. “No data that shows the wild birds were the vector of transmission has been made available at the present time,” Ip commented on ProMED-Mail, an internet bulletin board on emerging disease. “The same pattern of spread can just as easily be seen as from the major routes of human transportation.”

Adding to uncertainties, an investigation of an outbreak of bird flu on remote lakes in Mongolia by the Wildlife Conservation Society in August found that only 100 birds of more than 6000 on the lake died, suggesting either that the virus does not infect many birds in wild flocks, or the majority of birds that caught the virus remained healthy carriers. If wild birds are carrying H5N1, say European veterinary experts, the key to preventing outbreaks will be to prevent contact between poultry and wild birds. Free-range chickens have already been moved under cover in the Netherlands, which has had major outbreaks of other kinds of bird flu recently. But the vets in Brussels recommended that EU countries: hold their fire, increase their monitoring of flu viruses in wild birds, be ready to destroy infected birds, bring free-range animals inside if the virus is detected. They recommended that in at-risk situations poultry vaccination might be considered as a risk-mitigating measure.

New Scientist
September 13, 2005

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