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Avian Flu Controllable in U.S. as Long as Its Bird
Flu
By Krishna Ramanujan, Cornell
University
.gif) Oct.
6, 2005 - If a virulent strain of avian influenza ever struck the U.S.
poultry industry, this country probably would fare better than many
other nations, due to careful biosecurity procedures in force. As long
as the disease stays primarily a bird flu, officials have some control,
says Alfonso Torres, a government consultant on the issue. He is a
former U.S. chief veterinary officer and director of the Plum Island
Animal Disease Center, a high-security animal laboratory previously
operated by the USDA but now part of the Department of Homeland
Security.
But if the virus develops an ability to pass from
one human to another, the United States would have far less protection
as the world possibly faces one of the worst flu pandemics in history,
says Torres, who is director of the Animal Health Diagnostic Center and
associate dean for veterinary public policy at Cornell University's
College of Veterinary Medicine. .
Torres is among the U.S. health officials watching
the progress of this extraordinarily active virus (known as H5N1) as it
infects chickens in Asia and waterfowl in Russia.
"The fear is that if the virus changes or
recombines with a regular human flu, the virus may acquire the ability
to be effectively transmitted from human to human, then it could become
the big pandemic that everyone is very concerned about," he says. As a
consultant, Torres has held high-level policy discussions on avian flu
with the U.S. Department of Agriculture (USDA) and NATO, among others.
For now, the United States, like the rest of the
Western world, can only watch and prepare. Since January 2004, the known
human cases of avian flu have all struck in Southeast Asia -- out of 120
patients requiring treatment, about half have died. All of these
infections were contracted from chickens, with the exception of a few
cases in Vietnam where the source is unclear.
 A
natural reservoir for the avian flu virus is migratory waterfowl, and
infected birds have been found in Mongolia, Kazakhstan and Russia,
raising concern in the U.S. as the disease moves west. Although
waterfowl do not appear to be playing a big role in poultry and human
transmissions right now, they are being closely monitored.
"When experts look at the maps of the areas
affected by avian influenza in Asia and they look at the flying pathways
of migratory waterfowl, there is not an overlap," Torres observes.
Although waterfowl are the natural reservoir for all types of avian flu
-- meaning they are long-term hosts of these viruses and pass them among
each other, but often may not get sick or they develop mild infections
-- Torres says, "Waterfowl, at this point in time, are not the culprit
for what is happening in Asia."
Rather, the disease has spread in Asia in backyard
and low-tech poultry and duck production areas where people transport
infected chickens atop cars or on motorbikes to markets. There, sick
birds can infect other birds that then return home unsold. Also, people
who handle uncooked meat and infected birds can spread the flu virus
from bird to bird.
But in Asian poultry farms that use modern
biosecurity practices, like those in the United States that prevent
infectious diseases from spreading through flocks, the disease has not
spread. U.S. biosecurity regulations serve to minimize contact between
poultry and outside materials that could bring disease. For example,
measures can require poultry farm workers to take showers upon entering
a production facility and when they move between birdhouses on the farm,
and restricts them from owning pet birds at home and from hunting ducks
and other waterfowl.
While H5N1 strain most concerns researchers because
of its virulence and ability to be transferred from birds to people, all
strains that include the H5 and H7 proteins are now monitored because
they are most commonly affect poultry and they could potentially mutate
into more virulent, contagious forms.
International policy-makers are debating whether to
routinely vaccinate poultry with H5 or H7 avian flu viruses. They are
also deciding whether to include H5N1 in regular human flu vaccines,
which the U.S. government might also stockpile. Without advanced
stockpiling, vaccine production takes many months to ramp up. But
creating an effective vaccine in advance of a flu season is a little
like hitting a moving target, as flu viruses notoriously change, either
by slow genetic drifting through small mutations that add up over time
or by sudden shifts where two virus strains, for example avian and human
flu, swap genetic material in a commonly infected host cell. Torres
believes that a slow drift likely led to the first human case of avian
flu in 1997. Either way, flu vaccines are never sure-fire.
Pharmaceutical antiviral medications, like
oseltamivir (Tamiflu), can also control the disease in humans by
affecting the flu virus' ability to multiply in the patient, minimizing
its effects and allowing the body's natural defenses to get rid of the
infection. Government policy leaders are considering contracting with
drug companies to make millions of doses of such antivirals.
However, there is concern that indiscriminate use
of the drug would allow the H5N1 virus to develop resistance to the
medication, Torres says. One strategy could be to target only certain
populations, such as healthcare workers and first responders including
ambulance drivers, firefighters and police officers.
However, says Torres, the world still has much to
learn from the 1918 flu pandemic that killed more than 20 million
people. "One thing that happened in the so-called Spanish flu was a high
mortality rate among the healthiest individuals," he says. "The
healthier they were, the more susceptible they were."
That's because the Spanish flu virus caused an
exaggerated immune-inflammatory response in which cells release
chemicals that affect the permeability of blood vessels and cause fluids
to flood the lungs, leading to suffocation within hours.
Torres is currently working with an independent
policy and research think-tank in Washington, D.C., to organize a
conference early this winter to bring together experts from public
health, animal health, wildlife management and the poultry industry for
a larger discussion on avian flu.
"We need to have that four-way conversation," he
says. "We cannot do this in a vacuum."
Experiences with the West Nile virus, SARS and
monkey pox have taught health officials that in order to battle
epidemics, there must be coordination and dialogue among experts in a
variety of medical disciplines in conjunction with industry and the
private sector, Torres says.
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