Published Date: 2006-04-22 00:00:00
Subject: PRO/AH/EDR> Avian influenza, poultry vs migratory birds (14)
Archive Number: 20060422.1176
AVIAN INFLUENZA, POULTRY VS MIGRATORY BIRDS (14)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Fri, 21 Apr 2006 23:19:13 +0100
From: Mary Marshall <email@example.com>
Source: Seattlepi.com, 20 Apr 2006 [edited]
Ducks have a flu season just like people do -- and they're more
likely to be sick in the fall than in the spring. So authorities must
keep their guard up even if the government's mass testing of
migrating birds, beginning now in Alaska, doesn't spot the worrisome
H5N1 bird-flu strain right away.
That's a key warning from a new review of what scientists know -- and
don't know -- about how waterfowl constantly incubate influenza, and
how much of a role wild birds play as this deadly new flu strain
hopscotches around the globe. And it's one that federal wildlife
officials are taking into account as they determine how many birds to
test now, as ducks and other migratory species start flying into
Alaska's breeding grounds from Asia, and how many to test later in the year.
"If results in the spring are entirely negative, we still have that
opportunity in the late summer and the fall when many species of
birds come into closer contact with one another ... all using the
same wetlands at the same time rather than using more [discrete]
breeding areas," said Grace McLaughlin, who is helping to lead that
testing at the U.S. Geological Survey's National Wildlife Health
Center in Madison, Wis.
For birds, H5N1 already is an epidemic in much of the world, and
authorities fear it could finally reach birds in North America
sometime in 2006. H5N1 is most lethal to poultry, and outbreaks
originated from chickens in China, not from wild birds, said Ron A.M.
Fouchier, a virologist at the Netherlands' Erasmus Medical Center who
led the scientific review published in Friday's edition of the journal Science.
[Global Patterns of Influenza A Virus in Wild Birds,
21 Apr 2006: Vol. 312. no. 5772, pp. 384-388]
The question is what role wild birds now play as the virus hops
across continents. There's growing suspicion that international
smuggling of contaminated live poultry or poultry products, such as
fertilizer, may be playing a bigger role. But wild birds do play some
role, Fouchier said, pointing to dead swans found in parts of Europe
where no chickens were sick.
What isn't clear is whether the swans were sentinel species, the
victims that died after infection from a still unknown source, or
were actual flu spreaders.
In Europe [during the fall of 2005], scientists spent 3 months
testing 30 000 live wild birds and couldn't find the virulent H5N1
strain -- but they did find it in 500 of 2000 dead birds tested,
Fouchier said in calling for better global surveillance to quantify
and understand flu strains in birds.
The U.S.-based Wildlife Conservation Society, with some government
funding, is about to launch a global bird-testing network to help do
that, said William Karesh, chief of the nonprofit group's field
veterinary program. Meanwhile, as the U.S. steps up its effort to
detect H5N1's arrival, Fouchier's review does provide some
reassurance, McLaughlin noted: Over the years, there hasn't been much
mixing of Eurasian and North American strains of bird flu. Nor do
very many species fly from Asia into Alaska.
But, "the chance is certainly not zero," Fouchier said. "In America,
you cannot simply rely on the geographical separation of the continents."
Fouchier and colleagues in Sweden painstakingly detailed global
patterns of flu infections among wild birds, an analysis that
suggests that climate and migratory patterns coincide to spur spread.
Flu viruses like cold weather, and cold water - ducks and other birds
typically trade influenza through feces in ponds or lakes. Flu
viruses can live more than 30 days in near-freezing water but for no
more than four days in warm water. Migrating ducks in turn tend to
have the most flu infection when young, immune-naive birds are
congregating in early fall, to prepare for winter flight to warmer climates.
[Byline: Lauran Neergaard, AP]
[Members are strongly advised to read this excellent paper in
Science. - Mod.MHJ]