Are wild ducks Trojan horses with H5N1 flu?

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    Martin W

      Just sent this email to a disease expert who is perhaps new to H5N1 in wild birds, and wants to look for a species that can carry this highly pathogenic flu (to check info, see if maybe a species looks a good candidate as vector).

      After couple of emails, he suggested, "I personally don't know whether 100 wild geese or ducks infected with H5N1 would all die, or if, as the attached paper [authors inc Hulse-Post: "Role of domestic ducks in the propagation and biological evolution of highly pathogenic H5N1 influenza viruses in Asia"] shows, 80 would die and 20 would fly off with high path H5N1." My take on this notion – called domino theory by some lately: I skipped over this re the five clinically healthy geese, found to have H5N1, in the Ellis report ("Investigation of outbreaks of highly pathogenic H5N1 avian influenza in waterfowl and wild birds in Hong Kong in late 2002" – main outbreaks in two urban parks); but had noticed cited in US Geol Survey guy note to promed (questioning the supposed role of wild birds in spreading H5N1). Those geese would not have flown away – the Ellis report seems to me highly remiss in not noting the Anatidae (all of them I believe; certainly all geese) were ornamental birds, with clipped wings. I don't know why such a massive omission – it's noted for flamingo, but there were no ornithologists in co-authors or acknowledgements that I can see. Nor did Ellis et all remark that Little Egrets in Hong Kong mostly resident, so it seems no migratory birds involved in the outbreaks in the two urban parks. I've seen this Hulse-Post paper, thanks. Another attached. Yes, helping drive notions that wild ducks – esp mallard – carrying asymptomatically.

      Even Carol Cardona, US poultry disease expert who gave me "dead ducks don't fly" phrase some time ago, taking this as evidence that there's plenty of H5N1 in wild birds: I've queried her, sent a little info that contradicts this. [For 2003/04, I wrote article on my website, dead ducks don't fly: – H5N1 isn't a novelty here] The Vietnam ducks showing some natural selection – evolution to lower virulence [albeit not so natural]. But remains complex situation – indeed, lately 170 or more domestic ducks died in Vietnam. Higher virus shedding in trachea, low in faeces, seems to make chance of transmission low; can get transmission between ducks kept tightly together, but in wild? – I've never seen a duck sneeze, or any ducks French kissing.

      Then, in Croatia this autumn, some mute swans have evidently survived H5N1 – but also very low titres cloaca; other species sharing the fishponds not infected. Looking like another case in which H5N1 (Guangdong goose 96 lineage) an evolutionary dead end. [Where did the swans get H5N1? Not clear; but apparently European breeding birds, so they didn't carry from east-central Russia.] Some time ago I saw notion there might be a "relay race" – with birds infected, moving, maybe dying, but new birds then moving to keep the virus passing going. Lately seen this notion called domino effect/theory. But it''s not happening. This is not what's observed: instead, what happens is birds catch locally and, overwhelmingly, die locally; or maybe a few birds survive (those swans), but virus still not passed on.

      Maybe (surely say some) Mongolia cases show birds moving the virus a distance. But then, no further onward movement, only v minor local spread, and that was it. We're not seeing the deaths associated with H5N1 (Gdong96) – even if Trojan Horse (or "stealth bomber" to medical reporter Helen Branswell) were lurking around: there simply aren't the collateral deaths you'd see in susceptible species; and this virus does not arrive quietly, not unless – perhaps – you're a captive bird, especially chicken, that's been poorly vaccinated.

      As well as great yawning gap in dead and dying birds the Trojan domino proponents would predict, there are also those tests: well over 70,000 apparently healthy birds tested, yet only those v few Croatian swans that I know of healthy (and those a special case – not chosen for testing at random); plus four birds of four species in Russia (all hunted – so really healthy?) and, bizarrely, some tree sparrows in vicinity of some farms in China (I read paper on these quickly; seems they were healthy, but apparently had own version of virus – though does this reflect a virus strain in the poultry there?)

      I've seen Robert Webster, one of Vietnam ducks papers' co-authors, seems v gung-ho re H5N1 in wild ducks, and never mind the above evidence. Quoted as saying H5N1 widespread in Russian birds – I don't know why, emailed St Jude's re this but no reply. Lately Webster also saying H5N1 in flamingo in Kuwait showed migration towards Africa – yet this was evidently a captive bird. Very silly. Remains the case that nature has been experimenting with bird flus far longer than we have.

      And if hasn't produced a virus that's mild in some species, lethal to great many others, I don't believe we'll see such a virus sustained in wild conditions (Poultry farms very different, with vaccines now part of the mix there.) With poultry smuggled across much of world (from China reaching Italy and US, say), chicken manure dumped into fishponds, regular trade able to move infected poultry, virus surviving for days – especially when cooler – in faeces on eggs n cages and on people's boots etc, there's really no need to look at wild birds to find major vector of this H5N1 poultry flu.

      But for some people, there's grant money; while others surely find it convenient to blame wild birds – far easier than going after real culprits. For something that seems of genuine concern, see this in Globe and Mail:

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