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To understand the differences and
potential threats to U.S. bird populations, this fact sheet provides
definitions, a historical perspective and an outline of the U.S.
Department of Agriculture and U.S. Department of the Interior
efforts to detect the highly pathogenic H5N1 avian influenza virus
in wild migratory birds.
Background:
About the virus
Avian influenza viruses are classified by a combination of two
groups of proteins found on the surface of the virus: hemagglutinin
proteins, of which there are 16, H1-H16; and neuraminidase proteins,
N, of which there are nine, N1-N9. There are 144 possible
combinations or subtypes based upon this classification scheme.
Wild birds, in particular certain species of waterfowl and
shorebirds, are considered to be the natural reservoirs for avian
influenza viruses. The subtypes that naturally occur in wild species
usually cause little or no disease. However, domestic birds are
generally more susceptible to avian influenza virus, and mutation or
recombination of a virus acquired from wild birds can increase its
disease potential in domestic birds.
Avian influenza strains also are divided into two groups based on
the pathogenicity of the virus -- the ability of the virus to
produce disease.
Low pathogenicity avian influenza: Most avian influenza strains
are classified as low pathogenicity and cause few clinical signs in
infected birds. Low pathogenicity avian influenza generally does not
pose a significant health threat to humans. However, this type is
monitored because two strains, H5 and H7, can mutate into highly
pathogenic forms.
High pathogenicity avian influenza: This type of avian influenza
is frequently fatal to birds and easily transmissible between
susceptible species. The strain that is currently of concern in
Asia, Europe, the Middle East and Africa is the highly pathogenic
H5N1 virus.
Timeline
Since 1997, when it first appeared in Hong Kong, federal wildlife
experts and public health officials have been monitoring the spread
of the highly pathogenic H5N1 virus.
Since 1998, USDA, in partnership with the University of Alaska,
has tested over 12,000 wild migratory birds in the Alaska flying
route and almost 4,000 wild migratory birds in the Atlantic Flyway.
All birds have tested negative for the highly pathogenic H5N1 virus.
The Department of the Interior and USDA stepped up wild bird
monitoring and testing programs when the highly pathogenic H5N1
virus spread throughout Southeast Asia and Russia.
Since summer 2005, Department of the Interior biologists have
been working with the state of Alaska to sample migratory birds for
H5N1 in the Pacific Flyway. The department has tested more than
1,700 samples from more than 1,100 migratory birds. There have been
22 avian influenza isolates identified, but none have been highly
pathogenic.
In August 2005, as part of the president's national strategy for
pandemic influenza preparedness, the USDA and the Department of the
Interior convened a joint working group with the U.S. Department of
Health and Human Services, the state of Alaska, and the
International Association of Fish and Wildlife Agencies to develop a
national strategic plan for early detection of H5N1 highly
pathogenic avian influenza should it be introduced into North
America by wild birds.
The wild bird plan:
Plan overview
The interagency strategic plan, developed by wildlife disease
biologists, veterinarians and epidemiologists, provides a unified
national system for conducting monitoring for H5N1 highly pathogenic
avian influenza in wild migratory birds throughout the United
States. The plan serves as a guide to all federal, state, university
and nongovernmental organizations involved in avian influenza
monitoring, by providing standard procedures and strategies for data
sampling, diagnostics and management.
Five strategies of the plan
The plan targets bird species in North America that have the
highest risk of being exposed to or infected with highly pathogenic
H5N1 because of their migratory movement patterns. Key species of
interest include ducks, geese and shorebirds.
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 If wild birds are or become able to effectively move the disease
over great distances, scientists believe introduction of H5N1 into
the United States would most likely occur in Alaska, where there is
significant mixing of Asian and North American birds. Therefore, the
interagency strategic plan recommends a prioritized sampling system
with emphasis first in Alaska, the Pacific Flyway and Pacific
islands, followed by the Central Flyway, Mississippi Flyway and
Atlantic Flyway. The five strategies are:
1. Investigation of morbidity and mortality in wild birds: The
systematic investigation of significant numbers of sick or dead
birds offers the highest and earliest probability of detection if
the highly pathogenic H5N1 virus is introduced into the United
States by
 migratory birds. Biologists and veterinarians in state and
federal wildlife and natural resource agencies, along with animal
health agencies and organizations, are prepared to detect and
respond to such discoveries. In the event that a highly pathogenic
H5N1 is detected in wild birds, USDA will identify and monitor
domestic poultry and swine operations in the area and minimize
contact between the wild birds and domestic animals.
2. Monitoring live, apparently healthy wild birds: This effort
targets wild birds in North America that represent the highest risk
of being infected with highly pathogenic H5N1 avian influenza
because of their migratory movement patterns. Species that will be
sampled include birds that migrate directly between Asia, Oceania --
including Hawaii, U.S. Pacific territories and freely associated
states -- and North America, and birds that might be in contact with
species from areas in Asia with reported avian influenza outbreaks.
This includes sampling live-captured, apparently healthy wild birds
to detect the presence of highly pathogenic H5N1 virus. Data
collected in Alaska will be combined with data from additional bird
captures to provide a broad species and geographic monitoring
effort. In 2006, USDA, the Department of the Interior and their
cooperators plan to collect 75,000 to 100,000 samples from live and
dead wild birds.
3. Monitoring hunter-killed birds: Hunter check stations operated
by the Fish and Wildlife Service and state natural resource agencies
for waterfowl hunting provide an opportunity to collect additional
samples to test for the presence of highly pathogenic H5N1 and other
subtypes of avian influenza. These samples supplement the targeted
monitoring samples from live wild birds and focus on species that
are most likely to have been exposed to highly pathogenic H5N1
viruses in Asia, have relatively direct migratory pathways from
those areas to the United States via Alaska or directly to the
Pacific Coast, or that mix in migratory staging areas in Alaska with
species that could bring the virus from Asia. Collection of samples
from these species will occur at hunter check stations in the lower
48 states, as well as Alaska, during hunting seasons in areas where
these birds gather during migration or overwintering. Samples also
will be collected from wild birds taken by native Alaskans during
the spring subsistence hunt. The U.S. Geological Survey, Fish and
Wildlife Service, and USDA are working with the four migratory bird
flyway councils to enhance sampling plans for hunter-killed birds.
4. Use of sentinel animals: Two groups of animals used as
sentinels in avian influenza monitoring programs could provide early
detection of the highly pathogenic H5N1 virus along migratory
flyways in the United States. Poultry flocks reared in backyards
(raised for noncommercial purposes) have been evaluated for diseases
of interest to nearby commercial poultry operators as a monitoring
method. Also, duck flocks can be placed in wetland environments
where they may commingle with wild birds. The ducks are then
monitored and tested for avian influenza viruses.
5. Environmental sampling of water and bird feces: Waterfowl
release avian influenza viruses through the intestinal tract, and
the virus can be detected in both feces and water in which the birds
swim. This provides a means of virus spread to new avian hosts and
potentially to poultry or other livestock. Analysis of both water
and fecal material from waterfowl habitat can provide evidence of
avian influenza circulating in wild bird populations. In 2006, USDA
and others plan to collect 50,000 samples from high-risk waterfowl
habitats across the United States.
Benefits of monitoring data
In addition to providing an early warning system for disease
occurrence in U.S. wild birds and domestic poultry, the monitoring
data will be used to create a national database that incorporates
and tracks all avian influenza data collected from wild birds in the
United States. The database will be available to all agencies,
organizations and policymakers involved in avian influenza
monitoring and response. The data collected in this system will be
used by scientists to develop a better understanding of the movement
of avian influenza viruses among wild and domestic animals, improve
risk analyses, and target monitoring strategies to track regarding
future avian influenza spread.
[U.S.
Department of Agriculture news release] |
