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This chapter focuses on the global phenomenon of
avian influenza, its impact on the poultry industry, and potential
means to control influenza transmission among birds and mammals. The
chapter begins with a review of the activities of the Office
International des Épizooties (OIE; also known as the World Organisation
for Animal Health)
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surveillance focused on the subset of avian
influenza viruses that pose significant risk of infecting humans,
including certain viruses of low pathogenicity in poultry. The chapter
concludes with an example of a low-pathogen avian influenza outbreak in
a group of commercial poultry farms and the steps the industry took to
contain further spread of the virus, minimize the risk of exposure, and
monitor and prevent further infections.
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Promotion of the safety of world trade in animals
and animal products The OIE develops standards for application by
Member Countries to protect themselves against disease incursions as a
result of trade in animals and animal products, while avoiding
unjustified sanitary barriers. These standards are developed by experts
from Member Countries and from the OIE’s network of more than 160
Collaborating Centers and Reference Laboratories.
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Firmly convinced that the best way to reduce human
exposure to the virus is to eliminate the virus at source—that is, from
animals, including wild birds—the OIE strives to assist Member
Countries in providing expertise particularly in the following areas:
disease surveillance, early detection, early warning and notification,
quality and evaluation of veterinary services, diagnosis, surveillance,
control strategies, and international trade in poultry and poultry
products. OIE Reference Laboratories and Experts The OIE is
coordinating a worldwide network of some 150 Reference Laboratories and
13 Collaborating Centers and more than 300 experts in various animal
diseases.
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. The Terrestrial Code provides the governments and
the Chief Veterinary Officers of OIE Member Countries with
recommendations for establishing national health measures or rules
applicable to the importation of animals and animal products with
respect to OIE listed animal diseases in order to avoid importation of
pathogens while avoiding unjustified sanitary barriers.
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The results of this evaluation can help provide the
importing country the assurance that information on sanitary/
zoosanitary situations provided by the veterinary services of an
exporting country is objective, meaningful, and correct. Evaluation of
veterinary services has gained further importance since the ban on
imports of poultry and poultry products from several southeast Asian
countries following the avian
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As mentioned earlier, the OIE provides standards,
guidelines and recommendations to assure the sanitary safety of
international trade in animals and animal products to avoid the
transfer of agents pathogenic for animals or humans while avoiding
unjustified sanitary barriers. In this context, the OIE is fully aware
of the constraints faced by countries wishing, for example, to export
fresh poultry meat.
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OIE has provided and will continue to provide
expert assistance to southeast Asian countries to improve surveillance
and monitoring systems to control the disease. The OIE advises that
countries establish programs to monitor high-risk avian populations,
such as live bird markets, fighting cocks, and other markets selling
wild birds.
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This has been particularly important during the
recent influenza outbreaks in southeast Asia, when consumption of these
commodities fell drastically, threatening millions of farmers who
depend almost entirely on subsistence animal farming for their
livelihoods. Therefore it was important to restore consumer confidence
in poultry products.
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Isolation of virus from other wild birds is
completely overshadowed by the number, variety, and distribution of
influenza viruses isolated from waterfowl. The highest rate of
detection of influenza virus is from ducks.
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Control programs for virulent strains of avian
influenza viruses therefore should be focused on biosecurity of poultry
populations and protection of humans exposed to poultry. Continual OIE
Involvement The OIE continues to monitor the worldwide AI situation
closely, paying particular attention to southeast Asia, where the
disease has far more economic and possibly more public health impact.
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The primary risks for introduction into commercial
poultry include: (1) direct access to wild birds infected with AI
viruses, (2)
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. The reservoir for genes of all type A influenza
viruses circulate in wild bird populations, principally waterfowl
(Order: Anseriformes)
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, but a few have been HP, especially when isolated
from wild birds trapped on poultry farms affected with HPAI. Common
poultry species, including chickens and turkeys, are not natural hosts
for avian influenza viruses (Hopkins et al., 1990; Suarez, 2000)
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Turkeys are susceptible to swine influenza viruses,
and having a turkey farm and swine farm in close proximity is a risk
factor for the introduction of swine influenza to turkeys. Infections
with both classical H1N1 swine influenza and the more recent
reassortant H1N2 and H3N2 swine influenza viruses have been reported
(Suarez et al., 2002; Wright et al., 1992)
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Many live bird markets are never free of birds, and
a continuous cycle of infection can be maintained, with the virus
continuing to become better adapted to chickens. The virus in the live
bird market system, although generally believed to be separate from our
commercial poultry system, has been a nidus of infection for spread to
our commercial poultry sector.
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In a nationwide survey of commercial poultry
through the National Poultry Improvement Plan in 1997 (Personal
communication, Andy Rorer, National Poultry Improvement Plan, U.S.
Department of Agriculture, April 28, 2001)
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The live poultry market system continues to be a
major source of AI viruses and risk for introduction to the commercial
poultry operations. Avian Influenza Vaccines The AI vaccines provide
protection from clinical signs and death, but protection is
hemagglutinin subtype specific such that H5 AI vaccines only protect
against the H5 subtype, and so on.
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In 2001, 2,797,000 doses of H1N1 or H1N2
inactivated AI vaccine was used in turkey breeders to prevent infection
by swine influenza viruses (Table 4-2) (Swayne, 2001)
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Finally, the H5N1 HPAI viruses of Asia have been
the primary focus as the next potential pandemic influenza viruses.
However, we must remember that the previous three pandemics (1918,
1957, and 1968)
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TABLE 4-4 Data on Virus Replication and Mortality
in BALB/c and CAST/Ei Mice Following Intranasal Inoculation with Two
Low- and One High-Pathogenicity AI Viruses Groups Mouse Strain BALB/c
CAST/Ei Mortalitya Virus Isolationb Mortalitya Virus Isolationb Trachea
Lung Trachea Lung Control 0/2 0/2 0/2 0/2 0/2 0/2 PA/11767/97 (H7N2)
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The H6N2 low-pathogenicity strain of avian
influenza virus, which infected commercial poultry in California, is
not a strain regulated by either the California Department of Food and
Agriculture (CDFA)
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focused on specific viruses for a very good
reason, this is a rather arbitrary decision and one that has limited
the study of the AI viruses that are the most prevalent among avian
species. The Spread of AIV Among Commercial Poultry Farms Commercial
poultry companies are first and foremost businesses.
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. Both of these populations, the game fowl and the
birds produced for live bird markets, have the potential to become
reservoirs of virus for commercial poultry populations.
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Multiple pickups from different farms on the same
day are not allowed Manure should be pushed to the edge of the property
for pickup Traffic patterns should be established that avoid
interaction between manure trucks and other farm traffic Scheduling
should be done to avoid clean traffic Manure should not be spread or
stored close to any other poultry Marketing of eggs Dedicated racks and
flats will be used for each ranch Racks and flats from different
ranches will not be commingled Flats will be washed and disinfected at
the processing plant Rack washing at the processing plant is strongly
encouraged Feed mills and feed delivery Feed trucks should be cleaned
and disinfected at the feed mill They should be kept away from “clean”
areas of the production facility They should be cleaned and disinfected
again when they enter a facility Drivers should be either kept away
from “clean” areas or provided with protective clothing All trucks and
equipment leaving a facility should be cleaned and disinfected before
exiting the facility if suspect or positive flocks are present Movement
of crews A representative of the poultry company will monitor all work
performed by crews to ensure that the following rules are observed:
Protective clothing and footwear provided by the ranch must be worn
Hand washing is required before handling birds Crew vehicles should be
cleaned and disinfected before they enter a facility or, preferably,
they should be left off site Mortality disposal Onsite cremation or
composting are the preferred methods of mortality disposal Use
renderers safely, if they must be used Tarp trucks Put mortality pickup
at the edge of the property Coordinate the routing of the truck to
avoid “clean” farm traffic
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Keep unnecessary visitors off the farm Visitors
should wear protective clothing to enter the facility A consistent
visitor policy should be established for all premises Keep a logbook of
visitors The producer participants in the plan were also required to
Monitor for new infections with the following surveillance of their
flocks: When there is little risk of infection, flocks will be tested
at slaughter During times when there is a risk of infection: 20 birds
will be tested for AI by AGID monthly Flocks must be checked daily for:
Decreases in egg production Increased mortality Clinical signs of
disease The next critical step is to determine what should happen with
a positive flock. Because there was no money for the indemnification of
their losses, depopulation of the flocks was not considered an option.
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may be moved to a positive lay ranch Suspect flocks
Get a diagnosis as soon as possible Contact your veterinarian, and/or
Submit birds to the diagnostic laboratory Notify your neighbors
Self-quarantine Positive flocks (currently infected and shedding avian
influenza virus) Notify neighboring poultry farms Self-quarantine Do
not move birds until the flock is no longer shedding virus Coordinate
movement of the flock to minimize risk Document route and time of
travel and let other producers know or Euthanize and dispose of the
flock on site (composting or cremation)
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Use of vaccine in flocks at risk of infection
Fulfill all CDFA/USDA requirements for biosecurity and flock plans
Using this voluntary plan, California controlled and eradicated H6N2 AI
virus from commercial poultry flocks. The producers in the state soon
learned that not telling each other about AI virus infections resulted
in the spread of the outbreak.
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has raised the profile of live bird markets.
Although surveillance has been increased, disease control measures have
been established in only a few locations (Mullaney, 2003)
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2000. Distinct pathogenesis of Hong Kong-origin
H5N1 viruses in mice as compared to other highly pathogenic H5 avian
influenza viruses.
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2003. Sequence analysis of recent H7 avian
influenza viruses associated with three different outbreaks in
commercial poultry in the United States.
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2003. Multiple genotypes of nonpathogenic H6N2 influenza viruses isolated from chickens in California.
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