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Avian Influenza

Fowl Plague, Brunswick Disease, Bird Flu, Fowl Pest, Highly Pathogenic Avian Influenza, Low Pathogenic Avian Influenza, Peste Aviaire

Avian influenza (AI) is a highly contagious, reportable disease of chickens that is mainly a concern for commercial factory farms where excessively large flocks of birds are confined in over-crowded environments.

AI is caused by infection with type A influenza virus, which is a type of orthomyxovirus of the family Orthmyxoviridae. AI has a high pathogenicity (HPAI), and by H5 and H7 subtypes with low pathogenicity (H5/h7 LPAI).

AI has resulted in large economic losses in the worldwide poultry industry and is a continued threat to human health. AI viruses have been shown to naturally infect a wide variety of wild and domestic birds, especially free-living birds occupying aquatic habitats, such as waterfowl. Aquatic birds have been known to serve as a major reservoir of the influenza viruses, with the majority being low pathogenicity (low virulence) strains for chickens and turkeys.

Low pathogenicity avian influenza (LPAI) viruses cause the milder forms (mild respiratory signs) of avian influenza while highly pathogenic avian influenza (HPAI) viruses cause more severe forms (multi-systemic infections). Most birds infected with HPAI viruses do not survive but many infected with LPAI viruses can recover.

Clinical forms of AI range widely from low pathogenic (LPAI) to highly pathogenic (HPAI). Clinical signs can vary from a mild infection (chickens show loss of appetite, deceased egg production, mild respiratory disease, and diarrhea) for LPAI to severe respiratory, neurological, and gastrointestinal (GI) signs with HPAI (resulting in high mortality rates).

Diagnosis of AI

AI is diagnosed in chickens through the use of rapid diagnostic methods, such as agar gel immunodiffusion (AGID) or rtPCR. Virus isolation is considered to be the "gold standard" in confirming that birds have been infected by the AI virus.

How AI is Transmitted

AIV is transmitted through aerosol spread in the air, ingestion of influenza particles in nasal and respiratory secretions, fomites, or by direct contact with feces of infected birds.

Incubation Period for AI

The incubation period is 3-5 days and is dependent on the dose of the virus, the route of exposure, the species exposed, and the ability to detect clinical signs.

Clinical Signs

Decreased feed and water intake
Ruffled feathers
Unilateral facial swelling
Red or watery eyes
Change in voice
Open mouth breathing
Head tilt
Twisted neck
Weight loss
Sudden death
Nasal discharge
Decreased egg production
Blood-tinged discharge
Reddening skin
Dark colored feces
Pale comb or wattles
Focal ecchymosis


  • History
  • AGID
  • RT-PCR
  • Virus isolation
  • Antigen detection
  • HI


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
VaccineInactivated whole AI virus



  • Routinely test birds for AI
  • Biosecurity
  • Keep wild waterfowl away from chickens
  • Prevent direct contact with free-flying birds or their feces
  • 20 microg/dose of cochinchina momordica seed (ECMS) administered along with the influenza vaccine (H5N1)

Scientific References

Good Overviews

Risk Factors

  • Red poultry mite infestation, as mites are capable of transmitting the influenza virus
  • Exposure to high populations of wild birds, especially aquatic birds.
  • Poor sanitary conditions
  • Over-crowding
  • High Sress