- The World Health Organization (WHO) says
H5N1 avian influenza has infected birds in 14 more countries since the
beginning of this month [February 2006], and recent genetic changes in
the virus may have something to do with its rapid spread in birds. The
agency said countries that have reported their 1st cases of H5N1 infection
in birds this month, in chronological order, are Iraq, Nigeria, Azerbaijan,
Bulgaria, Greece, Italy, Slovenia, Iran, Austria, Germany, Egypt, India,
France, and Hungary. Authorities in Hungary confirmed today [22 Feb 2006]
that 3 dead swans were infected with the virus.
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- In a separate statement yesterday [21
Feb 2006], the WHO said, "Some recent evolutionary changes in the
H5N1 virus appear to have made control efforts more difficult and further
international spread of the virus in birds more likely." Among other
things, the agency said H5N1 viruses now may be able to infect some wild
birds without harming them, making it possible for migratory species to
carry the virus for long distances. In addition, H5N1 viruses have grown
tougher and more lethal to laboratory chickens.
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- The outbreak situations in the 14 countries
have varied nearly as widely as their geography.
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- Most of the affected European countries
have good veterinary surveillance and have found the virus only in a few
wild birds, with no evidence of spread to domestic birds, the WHO said.
At the other end of the spectrum, Iraq's bird outbreak was identified only
after a fatal human infection was found. In countries such as Azerbaijan
and Egypt, die-offs of domestic poultry heralded the spread of the virus.
Nigeria and India's [index] cases were found on commercial farms.
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- Other than Iraq, which has had 2 human
cases, none of the newly affected countries have reported any human cases.
However, the WHO said in another statement today [22 Feb 2006] that 15
patients with possible signs of bird flu are under observation in hospitals
in the area where India's outbreak occurred. The patients are being tested
for the virus as well.
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- In reporting on the H5N1 virus's evolution,
the WHO said viruses from recent avian outbreaks have shown "remarkable
similarity" to those found in migratory birds that died at China's
Qinghai Lake wildlife sanctuary starting in April 2005. "Evidence
is mounting that this event, which resulted in the deaths of more than
6000 wild birds, signaled an important change in the way the virus interacts
with its natural reservoir host," the agency said.
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- Before the Qinghai Lake die-off, the
virus caused only a few scattered deaths among migratory waterfowl, and
the latter were not known to carry the pathogen long distances, the agency
said.
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- Viruses from Qinghai Lake had a distinctive
point mutation that has been linked experimentally with greater mortality
in birds and mice, the WHO said. Viruses from the recent outbreaks in Nigeria,
Iraq, and Turkey, as well as from earlier outbreaks in Russia, Kazakhstan,
and Mongolia, are "virtually identical to Qinghai Lake viruses."
"It is considered unusual for an avian influenza virus causing outbreaks
in birds to remain this genetically stable over so many months," the
statement continues. "This finding raises the possibility that the
virus, in its highly pathogenic form, has now adapted to at least some
species of migratory waterfowl and is coexisting with these birds in evolutionary
equilibrium, causing no apparent harm, and traveling with these birds along
their migratory routes. "If further research verifies this hypothesis,
reintroduction of the virus or spread to new geographical areas can be
anticipated when migratory birds begin returning to their breeding areas."
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- The WHO stopped well short of assigning
to migratory birds the major blame for the virus's recent spread, a notion
that has been controversial. David Halvorson, DVM, a veterinarian in avian
health at the University of Minnesota in St. Paul, said today [22 Feb 2006]
that H5N1 is probably being spread both by the movement of poultry and
by the movement of wild birds, but no one is absolutely certain. "The
fact is we don't really know why it's being found in so many places so
suddenly," he told CIDRAP News.
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- Halvorson suggested that trains may play
a role in the spread of H5N1, as they have in past outbreaks. In the United
States in 1925, "People were shipping poultry to New York live bird
markets. Then, dirty, contaminated crates were being shipped back."
This contributed to the spread of a highly pathogenic avian influenza (HPAI)
outbreak. "I think that the trans-Asian railway system fits the temporal
and spatial pattern of virus distribution starting in July of last summer
[2005]," Halvorson commented. "For us in the Western Hemisphere,
it would be extremely unusual for water birds to be migrating thousands
of miles in July and August, a time when they are ordinarily taking care
of their young." Even today, it is normal to ship chickens by rail
in many places. Birds also can be found on buses and trucks under circumstances
that could contribute to spreading the virus, Halvorson said.
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- Most of the bird cases found in Western
Europe this month [February 2006] have been in wild swans, which has raised
puzzling questions. Halvorson listed some in an e-mail message: "Are
swans an indicator species? In other words, are they detecting (and dying
from) AI [avian influenza] in their environment? Or are they spreading
it around? Are they flying north or south? Are they both an indicator species
and also spreading it around?"
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- Jean Hars, a French veterinary epidemiologist
quoted in an Agence France-Presse (AFP) report yesterday [21 Feb 2006],
said the mute swan, the hardest-hit species in western Europe, is not migratory.
Hars said some whooper swans, a migratory species, on a German island in
the Baltic Sea were infected, but how they were exposed is a mystery, because
they stay in far northerly regions, where no H5N1 outbreaks have been reported.
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- In reporting on the evolution of the
virus, the WHO said the recent changes have not had any noticeable effect
on the disease in humans. "Human infections remain a rare event,"
the agency said. "The virus does not spread easily from birds to humans
or readily from person to person. As reported here yesterday [21 Feb 2006],
the agency said its investigation of human cases in Turkey has yielded
no evidence that viral mutations have changed the epidemiology of the disease
in humans.
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- In today's [22 Feb 2006] statement, the
WHO expressed concern about the virus becoming established in backyard
flocks, a known risk factor for human H5N1 infections. Halvorson echoed
the concern. "Clearly, it's in wild birds, whether they're picking
it up from poultry or spreading it themselves," he said. "We
have to separate our poultry from wild birds. It's essential. Some places,
it's going to be easy. In some places, it will be virtually impossible."
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