Don't blame the birds, experts say as FAO warns migrations spread avian flu (Pandemic-Birds) Sep 05 14:52 - CP - The Canadian Press
By Helen Branswell
TORONTO (CP) _ The UN's Food and Agriculture Organization renewed its warning Monday that migratory birds may be culprits in both the spread of avian influenza and threats to future geographic expansion of the deadly H5N1 strain.
But many wildlife authorities and avian influenza experts question the contention, saying wild waterfowl may play a significantly smaller role in the spread of the virus than the Rome-based agency and others suggest.
Don't be too quick to blame the birds, these experts warn.
They believe that feet and wheels, not wings, are behind the spread of the virus that has ravaged poultry flocks in Southeast Asia since at least late 2003 and was recently found in eastern Russia, Mongolia and Kazakhstan.
``My best guess is probably related to my experience, which is (that) humans account for more spread of influenza to domestic birds than wild birds do'' says Dr. David Halvorson, an avian flu specialist at the University of Minnesota. Halvorson and others believe that in many of the recent cases where wild birds were blamed for H5N1 outbreaks in domestic poultry, the migratory birds may actually be victims, not villains.
``They're the sentinels. They're not the reservoir that's spreading it around. They're infected because the poultry are infected,'' explains Dr. David Swayne, director of the U.S. Department of Agriculture's poultry research laboratory in Athens, Ga., that agency's main centre for the study of avian influenza.
An example may be the large die-off of wild birds at the Qinghai Lake reserve in western China earlier this year. As many as 6,000 birds were reported to have died; a number tested positive for the H5N1 virus. Molecular analysis of the viruses suggested the birds were likely infected by poultry in southern China.
Those who question the role of the migratory birds say they are a convenient scapegoat.
It's less embarrassing for a government to blame wild birds than to admit that its customs officers are turning a blind eye while farmers cross borders to unload infected chickens on unwitting buyers or as people smuggle sick fighting cocks to lucrative matches.
It's easier to blame a wild bird than to admit live poultry markets are serving as petri dishes, with infected birds passing the virus to uninfected ones which then transport it to previously untouched farms kilometres away.
``When you have an outbreak, sometimes you don't really know what the cause was,'' Swayne says.
``Nobody going to be upset with you if you say wild birds.''
He believes the recent die-off of migratory birds in Mongolia, in an area where domestic poultry is not found, represents the strongest case to date that wild birds may be capable of transporting the virus over long distances.
Even at that, he and others think too little is known about how many healthy birds are carrying it, how long they remain infected and how long they shed virus to make assumptions about their ability to take H5N1 to far-flung destinations such as the Indian subcontinent, Europe and Africa, as the FAO has predicted.
``Those are critical pieces of data that you need before you can really strongly make a claim that it's coming, for sure,'' Swayne says.
But the FAO's chief veterinary officer says the danger posed by further spread of H5N1 means authorities have to assume migratory birds are a risk and do everything possible to prevent wild water birds from mixing with domestic poultry flocks.
``Whatever you think about the scientific certitude _ and we are the first saying that there is a need to do a lot of investigation because there are too many grey areas _ we cannot, and the countries cannot, take the risk they don't play a role,'' Dr. Joseph Domenech says from Rome.
``Saying there is no risk is irresponsible.''
Domenech admits there is no smoking gun with which to indict migratory birds. But he argues the explosion of avian influenza in late 2003 and early 2004 _ when nine countries reported near simultaneous H5N1 outbreaks _ is suggestive of wild bird spread. ``It was not possible to explain everything with trade.''
But Martin Williams counters that if you superimpose the pattern of spread over migration patterns, the two don't mesh.
``When you looked at it . . . the timings of the migrations and the timings of the outbreaks just didn't fit at all,'' says Williams, an avid amateur ornithologist from Hong Kong who has been studying birds for decades and has taken up the cause of migratory birds on his website, www.drmartinwilliams.com.
At the heart of the scepticism about the role of migratory birds is the fact that highly pathogenic avian flu viruses _ in other words, those that can kill _ until recently were virtually never found in wild waterfowl. (From its first recorded appearance in southern China in 1996, H5N1 has been a high path virus.)
Some species of wild water and shore birds are the natural reservoir of avian flu viruses. But the viruses they carry are invariably of low pathogenicity or ``low path'' _ they don't kill their hosts.
When domestic poultry pick up low path viruses from wild birds, the viruses can mutate as they cycle through generations of domestic birds, ratcheting up pathogenicity in the process. The high path offspring can wipe out whole flocks of domestic poultry, but typically cannot infect wild birds.
H5N1 has defied this dogma on several occasions, causing several migratory bird die-offs in the wild and infecting and infecting and killing ducks in laboratory settings. The only previous time avian flu was known to have killed wild water birds was in 1961 in South Africa, where there was a die-off of terns.
Teasing out whether migratory birds are playing a role has been made more difficult by the fact that governments haven't always been entirely forthright about the scope, frequency and location of their avian flu outbreaks, obscuring patterns which might otherwise come into focus.
``Transparency by some countries of reporting the virus and the outbreaks has been a big problem in really trying to figure out what's the real epidemiology and how's this virus being spread around,'' Swayne says. INDEX: HEALTH POLITICS INTERNATIONAL SOCIAL
© 2004 The Canadian Press
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Re Domenech's comments: I've seen re foot and mouth disease outbreaks that spread thro UK and to some other places in Europe did not fit all that was known re transport - suggesting that unknown transport happened (as flying wild cows not available as scapegoats). Might be irresponsible to say there is zero risk from wild birds spreading bird flu. Irresponsible, too, to overplay the risk.