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Friday, August 11, 2006

Latest Thoughts on Bird Flu

In the past six months, we've learned a lot about how bird flu is and isn't spread. Here's a great summary of what we know and are still looking at from Richard Thomas of BirdLife International:

1) The highly pathogenic form (HPAI) of H5N1 arose in poultry and H5N1 remains almost exclusively a poultry disease.

2) The major spread of the virus is caused by the international poultry trade, as has been stated publicly more than once by the United Nations Food and Agriculture Organization. As such, the US Govt should be investing in tighter border security if it wishes to prevent H5N1 entering the country. The recent report about tonnes of Chinese poultry meat entering the New York restaurant chain shows the US is playing Russian Roulette with H5N1. It is not the only recent report of poultry/poultry product smuggling into the US from infected areas.

3) Four human deaths have been caused by close contact with wild birds: women who were plucking swans for feathers in Azerbaijan. All other human cases have been caused by close contact with infected poultry or (in a very limited number of instances) through human-human transmission.

4) The total number of wild birds infected is in the thousands (cf. hundreds of thousands, as opposed to millions of infected chickens).

The biggest possible wild bird outbreak is currently ongoing at Ubsu-Nur, a lake that straddles the Russia-Mongolia border where there are reports of up to 10-15,000 dead birds. However, there is no official Russian Govt confirmation of the outbreak being H5N1, and early on there were reports of many dead rodents and fish at the lake - so it could just all be poisoning.

Prior to Ubsu-Nur, the largest alleged "wild bird" outbreak was at Qinghai Lake in China (where up to 6,000 birds were reported dead - mainly Bar-headed Geese). However, in recent months we've learned that Bar-headed Geese have been farmed and released at the Lake and elsewhere in north-west China for at least a decade, so how many of the geese were wild birds is not clear, nor were many of the corpses tested and confirmed as killed by H5N1 - possibly, like Europe, only a small proportion of the dead birds had the virus].

5) All wild, migrant birds testing positive for H5N1 have either been dead or dying. There is no properly documented case of a wild bird carrying H5N1 asymptomatically.

It is true that some Tree Sparrows in China were found to be carrying HPAI H5N1, but not the Z-Genotype that's causing all the problems. They're also not migratory. The other widely-publicised "asymptomatic wild bird" case were six "wild, migratory ducks" at Poyang Lake, China reported by Chen. However, the authors are unable even to say which species these birds were; one of the possibilities they give (Spot-billed Duck) has a resident population at the lake. I can send a list of other flaws in their methodology - not least of which is that they did zero poultry testing around the lake].

6) The best evidence for long-distance movement of the virus by wild birds was in Europe in winter/spring 2006. The scattering of dead/infected wildfowl were consistent with movements of birds fleeing cold weather in the Black Sea/Caspian Sea regions. Poultry had been infected for months in these regions before the virus's appearance in wild birds. Our "best guess" is wild birds became infected in poultry farm factory outflows. [The Ruegen Island (German) outbreak is very strange and points to a local source].

7) The US Govt is probably wasting its money on testing wild birds in Alaska using its current methodology. All the reports I have seen refer to researchers taking cloacal swabs. Fouchier reported (at recent FAO-OIE conference on wild birds) that artificially infected ducks DID NOT EXCRETE THE VIRUS IN THEIR FAECES; it was only present (and detectable) in tracheal swabs. Hence, a negative result from a cloacal swab may be just a false negative.

8) The virus has been endemic in South-East Asia for more than a decade. More than 16,000 healthy, wild, migratory ducks in Hong Kong have been tested during that period - and all found to be negative for H5N1 (subject to the proviso above about cloacal testing). Similarly, more than 12,000 samples from birds in Alaska from 1998-2005 were all negative for H5N1.

9) The westwards spread of the virus from China to Eastern Europe follows no known wild bird migration pathway; nor does the timing (spring in the east, autumn in the west) follow a plausible migration route. The introduction to Africa (Nigeria) was unquestionably through trade.

10) If there was a significant danger of H5N1 introduction into the US through mixing of Asian migrants with American migrants in Alaska, why has there been no outbreak of H5N1 in major destinations for Asian migrant birds, such as the Philippines, Australia and New Zealand?

Japan and South Korea both experienced outbreaks following importation of infected poultry meat. After stamping the disease out through culling and tightening their borders, neither has experienced further outbreaks. The US should take note.

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