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Avian Influenza

Other Names: 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 viral infection of wild and domestic birds worldwide. Avian influenza viruses are classified as low pathogenic avian influenza (LPAI) or highly pathogenic (HPAI), based on their pathogenicity in domestic chickens. LPAI viruses cause milder disease, while HPAI result in more severe, multi-systemic infections. Once infected, the AIV replicates in the respiratory, intestinal, renal, and/or reproductive organs of the host.

Clinical Signs

Clinical signs of AI are highly variable and the severity of the infection depends on age, sex, host immunity, pathogenicity of the infecting virus, presence of secondary pathogens, and where the virus replicates in the body.
  • LPAI: In chickens, most infections with LPAI viruses affect the respiratory tract, especially the sinuses. Gross lesions are characterized as catarrhal, fibrinous, serofibrinous, mucopurulent, or fibrinopurulent inflammation, often accompanied by secondary bacterial infections. The bird's infraorbital sinuses may appear swollen and filled with mucous-to-mucopurulent nasal discharge. Hens may start laying abnormal eggs, often misshapen, abnormally fragile, and show loss of pigmentation. They may develop egg yolk peritonitis as a result of secondary complications due to the virus.
  • HPAI: HPAI viruses frequently replicate and cause damage to multiple visceral organs, and cardiovascular and nervous system. However, the presenting clinical signs will vary from bird to bird, depending on the amount of damage induced to the organs. Respiratory signs are less likely to occur then with LPAI virus infections. Nervous system signs most often include head and neck tremors, wry neck, inability to stand, and abnormal tilted head positions. There will be overall less activity among the birds who will appear very depressed and show reduced appetite.


AIV is excreted through the nasal and respiratory secretions (nares, mouth, conjunctiva), cloaca, and feces of infected birds into the surrounding environment. The virus is transmitted by direct or indirect contact with infected birds through aerosol droplets or exposure to virus-contaminated fomites.

Wild waterfowl are the primary hosts of influenza A viruses (IAV), especially mallard ducks. They act as asymptomatic carriers of LPAI viruses, and will shed high amounts of the virus in their feces, into the body of water they're swimming in. Since wild waterfowl are often carriers of the low pathogenic influenza virus, they are often a source of entry in flocks.


AIV is diagnosed in chickens through the use of several types of common laboratory diagnostic tests. Swabs taken from the chicken's oropharynx or cloaca work best. Virus isolation is considered to be the "gold standard" in confirming that birds have been infected by the AI virus.

Incubation Period

The incubation period for avian influenza virus 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

Ruffled feathers
Facial swelling
Red or watery eyes
Wry neck
Head tilt
Head and neck tremors
Sudden death
Nasal discharge
Decreased egg production
Pale comb or wattles
Focal ecchymosis


  • History
  • Laboratory tests

Reported Cases

  • Case 1: Avian influenza in a Parrot A 3-month-old chick infected with Avian influenza virus hemagglutinin subtype H5N2 with low pathogenicity was experiencing severe lethargy. He was admitted to the hospital and placed in quarantine. Supportive care treatment was administered. Although detection of H5 avian influenza virus in birds in the United States typically results in euthanasia of infected birds, an alternative strategy with strict quarantine measures and repeated diagnostic testing was used. The chick recovered from the initial clinical signs after 4 days and was released from quarantine 9 weeks after initial evaluation after 2 consecutive negative virus isolation and real-time reverse transcriptase PCR assay results. Ref


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.
AmantadineAdministered orally (25 mg/kg) or in drinking water (100 mg/L) x 10 days following infectionB Speer
Oseltamivir0.5 mg/kg PO q12h x 5 days, administered prophylactically to healthy birds in the event of an outbreak.B Speer
Rimantadine (Flumadine, Forest)100 mg/L drinking water, must be used before and during exposureB Speer
Baicalin (Scutellariae radix) extract100-450 mg/kg of dietZhang, Xinheng, et al. 2020; Ding, Yue, et al. 2014; Z Wu et al.,2020; Y Zhou et al., 2019; B Yin et al., 2021; M Bao et al., 2022; Z Hu et al., 2022
N-acetylcysteine (NAC)800 mg/kg BWA Valdiva et al., 2001; N Uchide et al., 2011;J Geiler et al., 2010
Allopurinol10-30 mg/kg PO, q12hT Akaike et al., 1990; Z Rehman et al., 2018
Resveratrol200-600 mg/kg dietN Uchide et al., 2011; L Liu et al., 2013
Green tea (Camellia sinensis)1% of dietN Uchide et al., 2011; Chen, Xingyong, et al., 2019



  • Routinely test birds for AI
  • Biosecurity
  • Keep wild waterfowl away from chickens
  • Prevent direct contact with free-flying birds or their feces

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 Stress