Download VIRAL - Orthomyxovirus type A

Avian Influenza
•A respiratory infection of chickens and turkeys that is
characterized by upper respiratory involvement, mortality and
decreased egg production in adults.
•Infects most species of birds .
•1983 outbreak of virulent AI (Fowl Plague) in chickens in
Pennsylvania and surrounding states resulted in $60 million
eradication program.
•Several more recent breaks, including Mexico and Hong Kong.
On January 22, 2012, China reported its second human death
due to bird flu. Pandemic flu viruses have some avian flu virus
genes and usually some human flu virus genes.
Both H2N2 and H3N2 are pandemic strains.
Influenza Viruses Etiology
VIRAL - Orthomyxovirus type A
They are enveloped, negative stranded RNA viruses
All subtypes (but not all strains of all subtypes) of influenza A
virus are adapted to birds.
Influenza A viruses can be divided into 15
Haemagglutinin (H) antigens. 9 Neuraminidase (N)
antigens.
• Extremely variable in virulence
• Extreme antigenic variability brought about by genetic
reassortment in host cells.
• 2 Pathotypes: HPAI, LPAI
Etiology
– H5 and H7 are the most dangerous
– Amino acid sequence at H cleavage site is
important
• Highly virulent AI viruses cause the disease fowl
plague
– H5N2 - Pennsylvania "break".
– H5N1 - Hong Kong outbreak – 1997-98
• These viruses are extremely virulent.
• Hens may be found dead on the nest.
Ecology of Avian Influenza Viruses
• The greatest variety of AI viruses has been
isolated from wild birds, particularly from
waterfowls.
• Serve as reservoirs and gene pools
• These birds perpetuate only viruses of low
pathogenecity
• Natural host of AI viruses to which the viruses
are well adapted.
• Waterfowls are resistant to the disease
induced by HPAI viruses.
Ecology of Avian Influenza Viruses
• Domestic Poultry does not appear to be the
natural host of these viruses, therefore the
degree of adaptation to the host is low and this
could possibly explain why documented virus
mutation has virtually always occurred in
domestic poultry
Incubation Period
• Variable - few hours to days
• Depends on virulence of the virus and the
route of exposure
Course of Disease
1-2 weeks - depends on strain of virus.
Method of Spread
• Contact with infected birds
• Waterfowl are the original reservoir
• Ethnic slaughter house and distribution also
very important
– Live bird markets are a problem
Morbidity
Variable
Mortality
• Usually doesn't exceed 10% unless fowl plague
(high path) virus.
• Then can reach 80-100% mortality.
Clinical Signs
Non-Specific:
• Decreased feed consumption
• Decreased egg production
• Mild to severe rales
• Sinusitis
• Edema of head and wattles
• Diarrhea
• Whitens the shell of broiler breeder eggs. Shell color isn't
being laid down in the oviduct. Destroy infected eggs.
Postmortem Lesions
non-specific:
• Variable depending on strain of virus.
• Sinusitis with mucopurulent to caseous
exudate.
• Fibrinopurulent pericarditis.
• Congestive, hemorrhagic and necrotic changes
on the skin and the intestinal tract.
• Hemorrhages in proventriculus and heart.
Differential Diagnosis
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Mycoplasma
Newcastle
Infectious Bronchitis
Ornithosis (Chlamydia psittaci )
Turkey rhinotracheitis (TRT)/ Avian
pneumovirus (APV)
• Determination of the H and N type and
virulence are essential for control programs
Diagnosis
• Serology
– Agar gel precipitation (AGP) and ELISA
• Detects all types
– Hemagglutination-inhibition (HI)
• Detects only homologous hemagglutinin type
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Virus isolation – hemagglutinating virus
PCR
Immunochemistry
Histopathology - non-specific, Clinical Signs
Treatment
None
Prevention and Control
• Biosecurity
– Isolation rearing.
– Depopulate infected flocks.
– All strains are reportable.
– Bury the birds.
• Vaccination
• Killed vaccines are available for certain approved
areas.
– Protect only against homologous H type
Control
• Biosecurity
– Quarantine
– Intensify disinfecting measures
• Monitoring/Surveillance
• Stamping Out / Depopulation
• Vaccination - only for LPAI and not for HPAI
because it might prolong the shedding of the
virus
• Proper Disposal