This course provides the information and resources needed
to recognize clinical signs and gross lesions that could be suggestive
of Avian Influenza.
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Welcome
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Purpose
The purpose of this training course is to provide the inplant inspection
team with the information and additional resources needed to recognize
clinical signs and gross lesions that could be suggestive of Avian
Influenza.
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Objectives
- Recognize the clinical signs associated with Avian Influenza.
- Recognize the gross lesions associated with Avian Influenza.
- Notification procedures if Avian Influenza is suspected.
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Avian Influenza
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Etiology
Avian Influenza viruses are members of the family Orthomyxoviridae.
The influenza viruses that belong to this family are classified
into types A, B or C. These types are based on differences between
their nucleoprotein and matrix protein antigens. The Avian Influenza
viruses belong to Type A.
Influenza viruses are further classified into subtypes according
to the antigens of the Haemagglutinin (H) and Neuraminidase (N)
projections on their surfaces. There are 16 Haemagglutinin subtypes
and 9 Neuraminidase subtypes of the Influenza A viruses.
The subtypes that are of concern are the H5 and H7 because of their
potential to mutate into highly pathogenic strains.
AI viruses can also be classified into low-pathogenicity (LPAI)
and high-pathogenicity (HPAI) based on the severity of the illness
they cause.
The Low Pathogenic form may go undetected and usually causes only
mild symptoms such as ruffled feathers and a drop in egg production.
However, some LPAI virus strains are capable of mutating under field
conditions into HPAI viruses.
The High Pathogenic form causes severe, systemic disease with high
mortality in chickens, turkeys, and other gallinaceous birds. The
HPAI virus is extremely infectious and once established, can spread
rapidly from flock to flock.
The strain that is currently causing worldwide concern is the HPAI
H5N1 due to the millions of birds that have died in Asia, Africa
and Europe. This strain has also infected humans, most of whom have
had direct contact with infected birds. |
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Transmission
Avian Influenza Type A viruses are distributed worldwide, with wild
shorebirds and migrating waterfowl, serving as the natural reservoir.
Many of the strains in wild birds are either non-pathogenic or mildly
pathogenic for poultry. However, through mutation or reassortment
of less virulent strains, virulent strains can emerge.
These viruses infect the gastrointestinal and respiratory tracts
of these birds. Even though they are infected with the virus, the
birds usually do not show signs of disease. The viruses are shed
in the feces and respiratory secretions. The virus can survive in
water and at low temperatures for weeks.
Susceptible birds become infected by contact with contaminated secretions
or excretions by either direct or indirect contact.
Domesticated birds may become infected through direct contact with
infected waterfowl, other infected poultry or indirectly by dirt,
cages, water or feed that is contaminated with the Avian Influenza
Type A virus.
Airborne transmission is possible if birds are in close proximity.
The virus can be introduced into the nares, conjunctival sac and
the trachea.
Once avian influenza is established in a domestic poultry flock,
it is a highly contagious disease. Infected birds excrete high concentrations
of virus in their feces and nasal and ocular discharges. After the
virus is introduced into a flock, the virus is spread from farm
to farm by the movement of infected birds, contaminated equipment
and people. |
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Clinical Signs
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Common Signs
The clinical signs and course of Avian Influenza Type A are variable
and are influenced by the virulence of the infecting virus, species
affected, age, sex, concurrent diseases and environment. In some
flocks, seroconversion may be the only evidence of infection.
Avian Influenza can manifest as respiratory, enteric, or neurological
disease with mild signs to a rapidly fatal fulminating disease.
With HPAI, the disease may appear suddenly and birds die either
without clinical signs or with minimal signs of depression, inappetence,
and ruffled feathers.
Other birds may show ataxia and torticollis. |
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The combs and wattles can be cyanotic and edematous, with petechial
or ecchymotic hemorrhages at the tips
Per orbital edema is often associated with the swollen combs and
wattles.
Hemorrhages and subcutaneous edema may occur on the hocks of the
birds.
The birds can also be excessively thirsty and have a watery white
to green diarrhea. |
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Layers
In layers, with HPAI, the disease may appear suddenly and
birds die either without clinical signs or with minimal signs of
depression and inappetence.
The sick birds typically sit or stand, in a semi-comatose state.
The hens at first may lay soft-shelled or misshapen eggs, but then
stop laying.
The mortality rate varies from 50 to 100%. Birds that do survive
are usually in poor condition and may resume laying after several
weeks |
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Broilers
In broilers with HPAI, like layers, the disease may appear
suddenly and birds die acutely or with minimal clinical signs.
Common clinical signs seen are severe depression, ruffled feathers,
inappetence, and a marked increase in mortality.
Respiratory signs include clear, mucopurulent or blood-tinged nasal
discharge, coughing and respiratory distress. |
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Turkeys
In turkeys, the clinical signs are similar to that seen
in layers and broilers. However, the course of the disease generally
lasts 2 to 3 days longer in turkeys.
This poult exhibits swollen sinuses which is a common clinical sign
in turkeys. |
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Gross Post Mortem Lesions
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Common Lesions
In the less acute form, significant gross lesions are frequently
observed.
Fluid may exit the nares and oral cavity as the bird is positioned
for postmortem examination.
The birds may have subcutaneous edema of the head and neck area,
which is evident as the skin is reflected.
The trachea may appear relatively normal except that the lumen contains
excessive mucous exudates.
There may also be hemorrhagic tracheitis similar to the lesions
seen with Infectious Laryngotracheitis. |
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When the bird is opened, pinpoint petechial hemorrhages are frequently
observed on the inside of the keel as it is bent back.
Petechia may cover the abdominal fat, serosal surfaces, and peritoneum.
Kidneys are severely congested and may occasionally be grossly plugged
with white urate deposits in the tubules. |
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Hemorrhages may be present on the mucosal surface of the proventriculus
particularly at the juncture with the gizzard.
The lining of the gizzard peels easily and exposes hemorrhages and
erosions underneath.
The intestinal mucosa may also have hemorrhagic areas which can
be seen on the serosal surface. These hemorrhagic areas are usually
associated with the Peyer's Patches and in the cecal tonsils.
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Layers
In laying hens, the ovary may be hemorrhagic or degenerated
with darkened areas of necrosis.
In birds that survive for 7 to 10 days, the peritoneal cavity is
filled with yolk from ruptured ova, causing severe airsacculitis
and peritonitis. |
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Broilers and Turkeys
Broilers and turkeys that die peracutely may not have significant
gross lesions other than severe congestion of the musculature and
dehydration.
If the birds do not die peracutely, there can be petechial and ecchymotic
hemorrhages in the trachea, epicardial fat, serosal surfaces and
intestines.
The spleen, liver, kidneys and lungs may have grey or yellow necrotic
foci. |
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Differential Diagnosis
- Velogenic Viscerotropic Newcastle Disease (VVND)
- Infectious Laryngotracheitis
- Acute bacterial diseases such as fowl cholera
- Escherichia coli
- All these diseases have similar clinical signs and post
mortem lesions.
However, in an area where AI is prevalent, such as during an
outbreak, a sound presumptive diagnosis can be made by flock
history, signs, and gross lesions.
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Slide Show
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Regulatory Actions
If you see something unusual, it is most important that you contact
the District Office as soon as possible. FSIS Directive 6000.1,
Rev. 1 provides specific instructions when you observe symptoms
of Foreign Animal Diseases or other reportable conditions.
You should be able to provide the producer’s name, address, and
county/parish and telephone number. Also provide a description of
clinical signs, number affected and any gross lesions observed.
The District Office will notify the Area Veterinarian in Charge
(AVIC) of APHIS or the State Animal Health Official (SAHO). The
SAHO or AVIC will determine how the case is to be handled and will
give the DO specific instructions at that time.
Follow existing FSIS procedures and retain or control any poultry
products until directed by APHIS.
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FSIS Directive 6000.1 Rev. 1 (PDF Only)
- Key Points
- Provides PHVs instructions to follow if FADs or
reportable diseases are suspected.
- Updated list of reportable diseases to include Lagomorphs.
- Clinical signs and gross lesions of FADs or reportable
diseases.
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Scenarios
Educating the media and the public about the complexities of avian
influenza as a disease among birds is one of USDA primary communications
objectives.
As part of this effort, USDA, in partnership with the Department
of Health and Human Services, Department of the Interior, and Department
of Homeland Security, have developed three scenarios in the event
of a detection and/or outbreak of highly pathogenic avian influenza
in the United States.
Each of these scenarios contains a series of key questions and answers
about animal health, guidance for the public, as well as a summary
of the actions USDA would take in the event of a highly pathogenic
avian influenza detection in the United States.
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Resources and Links
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Glossary (PDF Only)
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