Avain Influenza

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Avian Influenza (AI) is a contagious / infectious viral disease which can affect all species (90) of birds

Infection among domestic or confined birds is associated with a variety of disease syndromes:
✓ Subclinical
✓ Mild upper respiratory disease
✓ Reproductive failure (Loss of egg production)
✓ Severe acute highly fatal generalized disease
✓ Mortality and severity of disease depends on strain of virus


Family: Orthomyxoviridae
Influenza virus (Type A)
✓ Three main types;
✓ Type A (Most virulent group)
✓ Multiple species ( Birds & Humans)
✓ Type B ( Common & less virulent than A)
✓ Humans
✓ Type C (Different pattern of matrix proteins)
✓ Humans and swine
• RNA, enveloped , segmented virus , which agglutinates
chicken RBCs
• Inactivated by— heat, extremes of pH, dryness, formalin,
dilute acids & lipid solvents e.g detergents & disinfectants
• Viruses are released in oral/nasal secretions & faeces


✓ Strain classification is based on surface antigens i.e, hemagglutinin (HA) & neuraminidase (NA) subtypes
✓ 16 HAs & 9 NAs are reported & they are present in various combinations in avian isolates (H5N1, H8N4) making 144 possible virus subtypes
✓ Cross protection does not occur between subtypes
✓ Frequency of antigenic variation is high
✓ It occurs in 2 ways:
• Drift — minor antigenic changes in HA and/or NA
• Shift — major antigenic changes in HA and/or NA

Mutate frequently
✓ Antigenic drift
✓ Point mutations accumulated during virus replication
✓ Antigenic shift (Genetic re-ssortment)
✓ Hybrid virus emerges when cell infected with two different influenza viruses
✓ Gene segments of two A I viruses infect the same cells which results in the production of new combination of HA & NA
✓ Human, avian, swine, equine
✓ Transfer of influenza virus to a different species

✓ Virus is secreted from
• Respiratory system
• Conjunctiva
• Faeces
✓ Horizontal:
• Aerosol
• Faecal contamination of feed & water
• Direct contact between infected & susceptible birds (migratory waterfowl, shore birds, pet birds) (natural reservoirs)
• Wild/free living birds worldwide carry the viruses in their intestines, but usually do not get sick (natural resistance)
• Ducks, waterfowl and shore birds are most important reservoir, same bird can harbour 2 or more strains
• Live bird markets & exotic birds
• Swine flu (H1N1 & H3N2) to turkeys & humans
• Virus contaminated fomites
✓ Vertical: No evidence


extremely variable
•Subclinical (LPAI)
•Mild upper respiratory disease (LPAI)
•Reproductive failure (Loss of Egg production)
•Severe acute highly fatal generalized disease

• Extremely variable
• Pronounced depression &  feed consumption
• Huddling and ruffled feathers
• Mild to severe respiratory sign: coughing, sneezing, rales & excessive
lacrimation, sinusitis and depression
• ✓ broodiness of hens & ✓ egg production
HPAI; (mostly seen in chicken) H5 & H7
✓ Sudden onset and short course with mortality near 100% (peracute)
• Subcutaneous edema of head & face which may extend to neck and breast
• Cyanosis of wattles, comb & unfeathered skin
• Areas of diffuse hemorrhage on shanks and feet
• Nervous disorders i. e, convulsions, ataxia
• Mucoid Diarrhoea (green)
• Drastic decline in egg production


LPAI: Mild to moderate inflammation of trachea, sinuses, conjunctiva later airsacs are affected with MG infection
✓ In layers; ovarian damage and haemorrhagic & involution of oviduct
HPAI: Variable; Lesions may be absent with sudden death
✓ Congested carcass with dark red muscles, severe congestion of the
musculature and conjuctiva
✓ Edema of head, neck & swollen sinuses
✓ Cyanotic, congested, haemorrhagic & necrotic wattles & combs
✓ Congestion & haemorrhages on shanks
✓ Hemorrhagic tracheitis , congested & haemorrhagic lungs
✓ Haemorrhages on epicardium and coronary fat
✓ Petechiae in abdominal fat, mucosal & serosal surfaces
✓ Haemorrhagic streaks in proventriculus and erosion of gizzard mucosae
✓ Airsaculitis: Airsacs thickened & having fibrinous or caseous exudate
✓ Egg yolk peritonitis and haemorrhagic follicles in laying hens
✓ Severely congested kidneys
✓ Necrotic foci in Pancreas, spleen, heart & later kidneys, liver

hemarrhages on shanks
avian influenza of poultry
AI of poultry
Hemarrhages on shanks
hemarrhages on shanks
Avian Influenza of poultry
Cynosis of Comb and wattles

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