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.