Avian Influenza in Chickens: Symptoms, Reportability and What to Do

Avian influenza is caused by type A influenza viruses classified by their surface proteins (H and N subtypes) and their pathogenicity in chickens (HPAI vs. LPAI).

• HPAI (Highly Pathogenic): H5 and H7 subtypes that mutate to highly pathogenic form. HPAI H5N1 has caused mass die-offs in wild birds and commercial flocks across North America since 2021-2022. Mortality in affected flocks approaches 100% within 48-72 hours.
• LPAI (Low Pathogenic): Most H subtypes cause mild illness with low mortality. LPAI H5 and H7 strains can mutate to HPAI form after circulation, which is why all H5/H7 strains are reportable in the US regardless of pathogenicity.
• Wild bird reservoir: Migratory waterfowl (ducks, geese, shorebirds) carry AI viruses with few or no symptoms and shed virus in feces and respiratory secretions. Backyard flocks with outdoor access are at highest risk during migration seasons (spring and fall).
• Fomite spread: Contaminated boots, clothing, vehicles, equipment, feed bags, and wild bird feces on water sources all transmit AI virus between premises.

Do not attempt to diagnose HPAI yourself. If you observe sudden unexplained mass mortality or severe neurological signs in multiple birds, treat it as a potential HPAI emergency.

• Field signs of HPAI: Multiple birds found dead without prior illness. Survivors show neurological signs, facial swelling, and respiratory distress. Rapid progression from first death to widespread mortality within 24-48 hours.
• Reportable threshold: In the US, any suspected H5 or H7 influenza infection is reportable regardless of pathotype. HPAI is a federally notifiable foreign animal disease.
• Lab testing: Conducted by USDA APHIS National Veterinary Services Laboratories (NVSL) or state diagnostic labs. RT-PCR on swabs or tissues confirms AI and identifies the subtype.
• Do not move birds or equipment if you suspect HPAI. Movement restrictions are critical to prevent spread to other premises.

There is no approved antiviral treatment for avian influenza in poultry. HPAI requires a regulatory response, not a farm-level treatment decision.

HPAI response protocol: Call USDA APHIS at 1-866-536-7593 or your state veterinarian immediately. Federal and state officials will guide the response, which typically includes quarantine of the affected premises, depopulation of infected flocks, and indemnity payment to producers.

LPAI management: LPAI outbreaks may be managed with enhanced biosecurity, movement restrictions, and in some cases vaccination under USDA permit. Your state veterinarian will coordinate the response.

Antiviral drugs: Oseltamivir (Tamiflu) and other neuraminidase inhibitors are not approved for use in poultry and are not part of the regulatory response protocol.

• Practice rigorous biosecurity year-round, with enhanced protocols during waterfowl migration seasons (spring and fall). Migratory birds are the primary wild reservoir.
• Keep chickens housed or screened from contact with wild birds and their feces. Wild bird feces on water sources are a major transmission route.
• Disinfect boots and equipment at every entry to the poultry area. Use foot baths with virucidal disinfectant (iodine-based or quaternary ammonium).
• Do not share equipment, vehicles, or clothing between poultry premises without full disinfection.
• Report sick or dead wild birds near your flock to your state wildlife agency. Unusual wild bird mortality near backyard flocks in spring/fall is an HPAI warning sign.
• Know the emergency contact: USDA APHIS emergency line 1-866-536-7593.