71. Avian influenza.

Question 1

Occurrence?

Answer 1

Avian influenza Zoonotic, Notifiable

• In poultry, wild birds & exotic pet birds, subclinical or acute febrile disease with respiratory, enteric & CNS
• signs
• Occurrence: world-wide, mainly in intensive (outdoor) poultry farms
• All bird sp but different susceptibility:
• Waterfowl are less susceptible to the clinical disease
• WILD
• ducks, geese, seagulls etc. act as NATURAL reservoirs of virus & shed the virus

Question 2

Causative agent?

Answer 2

Causative agent

• Orthomyxoviridae, Influenza virus, Type A influenza viruses
• All HA & NA serotypes in different combinations were found in birds
• Forms
• Apathogenic avian influenza (AAI)
• Low pathogenic (LPAI)
• Middle pathogenic (MPAI)
• Highly pathogenic (HPAI)
• INTL notifiable
• STAMP OUT
• Haemagglutinin (HA) & neuraminidase (NA) subtypes
• HA subtype H1- H5
• NA subtype N1 -N9
• Certain serotypes are present only in waterfowl
• Certain serotypes cause disease in poultry more frequently
• H5 (e.g. H5N1, H5N2, H5N3, H5N8, H5N9)
• H7 (e.g. H7N1, H7N3, H7N4, H7N7, H7N9)
• H9 (e.g. H9N2)
• Low pathogenicity (virulence) strains ʹ LPAIV
• High pathogenicity (virulence) strains ʹ HPAIV
• Influenza viruses are unstable, variable & mutations often occur
• In birds
• Any type of HA ʹ subtype can be found
• Often H5, H7 HA ʹ subtype isidentified
• H5N1 (caused pandemic btwn 2003-2005) Æoutbreak
• Quandong 1996, Hong Kong 1997 later spread throughout Asia, Africa & Europe
• Chicken flocks & children
• Recent world epidemic (due to migrating birds)
• 2006-2007 outbreaks in Hungary

Question 3

Epizootiology?

Answer 3

Epizootiology

• (Wild) birds are natural hosts of AIV
• Clinical manifestations are rare (except H5N1)
• Bird sp differ in sensitivity
• Transmission through direct contact, saliva, faeces, natural waters
• Migratory birds can play a role in long-distance transmission (e.g. mallard,swan)
• In poultry farms LPAIV may be endemic without clinical signs
• Persist for long time in the water ʹ waterfowl often affected (oronasal transmission)

Question 4

Pathogenesis?

Answer 4

Pathogenesis

• Oronasal infection
• respiratory & enteric epithelia
• Shedding with excretes, faeces; sometimes long-term carry
• LPAIV: immunosuppression, enteric & resp signs
• HPAIV: blood vessel damages, generalised infections

Question 5

Clinical signs?

Answer 5

Clinical signs:

• in any bird sp., but mainly turkey, chicken, parrot, rarely waterfowl
• LPAI HPAI
• Clinical signs Incubation: 1 ʹ 2 weeks
• Milder enteric, respiratory signs
• Immunosuppression : 2dary bacterial
• (Mycoplasma, Chlamydia)
• Lower mortality
• Incubation 1 ʹ 3 days
• Mass morbidity/mortality
• Edema, skin hemorrhages, respiratory signs, cyanosis
• Bloody diarrhoea, catarrhal
• CNS: Convulsions, torticollis, paralysis
• Pathology
• Histopathology
• Milder inflammatory lesions
• Bacterial complication
• Generalised haemorrhages (serous surfaces, mucosal
• surfaces, skin)
• Haemorrhage & inflammatory processes in the airways,
• in the lungs & in the enteric tract
• Necrotic pancreatitis (goose, H5N1)
• Serous, lympho-histiocytic encephalomyelitis

Question 6

Diagnosis?

Answer 6

Diagnosis

• Signs, pathology lesions ʹ suspicion
• Communicable disease ʹ lab tests are necessary
• Faeces, oral swab, dead bird
• RT-PCR, virus isolation (embryonated eggs), HA
• Pathogenicity:
• HPAIV ʹ IV pathogeny index >1.2 or mortality >75%; HA gene protease cleavage
• site sequence determination
• Serology: HAI, ELISA, VN
• Infection tests will be done with different isolates to decide if it is HPAIV/LPAIV strain

Question 7

Differential diagnosis?

Answer 7

Differential diagnosis

1. Newcastle disease ʹ lab tests
2. Infectious bursal disease ʹ age, no CNS signs
3. Aviadenoviruses (inclusion body hepatitis) ʹ course, mortality
4. Duck plague (herpesvirus) ʹ AI is usually subclinical in ducks

Question 8

Treatment and control?

Answer 8

Treatment (LPAI)

• Movement restrictions
• AB against bacterial complications
• After production slaughtering, cleaning, disinfection ʹ
• NO germinative infection!

Control:

• movement restrictions,
• stamping out,
• cleaning,
• disinfection

Question 9

Prevention?

Answer 9

Prevention

• (HPAI) ʹ Notifiable!
• In Europe:
• closed farming, ban on importation of living birds & raw poultry meat from
• endemic countries
• Asia, Africa:
• destruction of infected flocks, disinfections, preventative vaccinations with
• inactivated H5N1 or H5N2, H9N2, fowlpox-AI-H5
• VACCINE FORBIDDEN!!
• R vaccine hides the fact that the virus is there, preventing serious symptoms & economic
• consequences = danger to humans