Much Ado About Bird Flu
Fatbirder?s especially commissioned fact fileWhile evidently viewed as a distant issue to most birders as it circulated in east Asia (since 1996, but especially during 2003/2004), the H5N1 form of bird flu has hit the headlines with outbreaks reaching eastern Europe. Various news reports tell of fears that this bird flu could transform into a human pandemic virus, causing many tens of millions of human deaths.
Migratory birds are fingered for spreading flu: there are fears that waterfowl from Russia might bring H5N1 to western Europe, also – eventually – to the US.
Here, at Fatbirder’s request, is an attempt at some perspective – a view from Hong Kong, where H5N1 became the first flu known to transmit directly from poultry to humans (killing six of 18 people known to have become infected, in 1997); Hong Kong also became the first place to blame wild birds for spreading H5N1.Bird flus, human flus, disease factories, and evolutionary biology
Bird flus are common – but naturally occurring forms are typically mild, causing few or no apparent problems. (Only known natural outbreak causing mortality was in Common Terns at a colony in South Africa, in 1961.) Waterfowl – ducks, geese and swans – are among the main carriers of bird flus, which is transmitted through faeces.
Bird flus can infect poultry; and can occasionally then evolve to become virulent, highly pathogenic strains, perhaps best termed Poultry Flu. Hitherto, outbreaks have been halted by slaughtering infected flocks, so exterminating the strains. But the now infamous H5N1 strain has survived for almost a decade since being first discovered in a farm goose in south China in 1996.
This evolution to virulence fits the predictions of evolutionary biology: if a disease such as flu can (readily) transmit from even very sick individuals, it can evolve to become more dangerous. This was evidently the case on the Western Front of World War One, where flu evolved into a lethal form that was very efficient at transmitting between, and even killing, people. It’s also the situation in poultry farms.
So, evolutionary biology predicts wild bird flus will be mild, as is the case. And, wild birds should be highly inefficient at harbouring H5N1 – since Dead Ducks Don’t Fly. Indeed, a Wildlife Conservation Society team investigating outbreaks in Mongolia concluded the disease was “self-limiting” in wild birds.Wild Birds as Scapegoats
When Hong Kong experienced die-offs among ornamental waterfowl in two urban parks, caused by H5N1 in 2002/2003, the government was quick to blame wild birds. But evidence for this is scant; and the conclusion apparently ignored outbreaks around the same time in local farms, while the tens of thousands of wild waterbirds at nearby Deep Bay were unaffected (thousands of wild birds have been tested for H5N1 here; and while it has been found in a handful of dead birds, no healthy birds have tested positive).
During 2003/2004, H5N1 spread quickly and widely in east Asia. Again, wild birds were typically blamed; but again, the evidence was scant, or even downright contradicted notions birds were really to blame. Instead, it seemed wild birds were victims, not vectors.
The outbreaks from spring 2005 have likewise been (mostly) blamed on migrating birds. Here, it seems they may be responsible for outbreaks in Mongolia and Romania; but this is perhaps not certain.
H5N1 is not the only highly pathogenic influenza strain whose spread has been blamed on wild birds, or for which wild birds have looked like potential vectors. There have been such cases in the US/Mexico, in Australia, and the Netherlands. In each case, wild birds were exonerated.
Instead, trade – both legal and illegal, involving poultry and wild birds – seems the real culprit for moving Poultry Flu. Is Birding Safe?
With low numbers of wild birds known to be infected by H5N1 – even in east Asia – and (all?) of these sick birds quickly dying, birding is surely safe.
Are We All Going to Die?
As mentioned above, it appears unlikely or even impossible for a monster flu to evolve today. With H5N1 transmitting only with great difficulty between humans, even a pandemic of any sort is perhaps unlikely. Fingers crossed!
For further information take a look at:
Dead Ducks Don’t Fly – mainly re 2003/2004 outbreaks in Asia http://www.drmartinwilliams.com/birdflu/birdfluintro.html
H5N1 Poultry Flu and migratory birds forum http://www.drmartinwilliams.com/index.php?option=com_simpleboard&Itemid=137&func=showcat&catid=7
Birds Korea and Poultry Flu http://www.birdskorea.org/poultryflu_mainpage.asp
Birds Korea Poultry Flu Position Statement http://www.birdskorea.org/fluupdatesept05.asp
Avian influenza and birdwatchers http://www.bto.org/survey/webs/avianinfluenza.htm
This article was written by: Dr Martin Williams - Hong Kong
4th July 2014