On Wed, Oct 19, 2005 at 12:40:35AM +1000, Dion Hobcroft wrote:
> As bird flu reaches new media heights it is valid to realise that it
> is primarily a virus of ducks that to my knowledge has never been
> reported in Australian wild ducks. It is also important to realise
> that while migratory shorebirds have been implicated this has never
> been confirmed and is pretty unlikely to be confirmed as it is largely
> a duck virus. ...
I'm going to disagree (at length sorry). Wild birds are a reservoir
for many influenza strains and there are good reasons to believe they
are the vector for some outbreaks of highly-pathogenic avian influenza
strains in domestic birds outside Australia.
Anatidae (ducks & geese) are definitely the group where influenza has
been mostly commonly observed but significant rates of infections have
been found at some times in some species of Charadriiformes (waders),
e.g Ruddy Turnstones. Avian influenza has been found in roughly 100
bird species from at least 12 orders. Its rare in passerines but it has
been recorded in European Starlings raising concerns they might become
a vector in agricultural areas.
The current highly pathogenic H5N1 strain has been reported in wild
ducks, geese, gulls, cormorants and a Peregrine. It has, of course,
not been found in Australia, but over 10 avian influenza strains have
been isolated from wild birds in Australia. Hosts include shearwaters,
terns, ducks and coots. There are suggestions avian influenza isn't as
prevalent in Australia as some other countries.
There have been 5 outbreaks in Australian domestic birds of highly
pathogenic influenza - all the H7 subtype which hasn't been isolated
from wild birds in Australia. In one of these outbreaks bird on an
adjacent Emu farm were also infected. There was speculation the vector
might be Emus and/or waterbirds but there isn't evidence for this
so the vector for these H7 outbreaks remains a mystery.
The geographic range of observations of this current H5N1 strain is
spreading rapidly, suggesting wild birds might be the vector. This
certainly doesn't mean long-distance migrants are involved.
Presumably wild birds have conveyed influenza into Australia on
previous occasions.
Australia isn't a likely arena for the evolution of H5N1 human-human
transmissability so our major concern is that this arises elsewhere and
is conveyed into Australia by humans.
Andrew
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