Section 1. Avian Influenza Facts

Site: Extension Foundation Online Campus
Course: Avian Influenza Biosecurity for Youth and 4-H Members
Book: Section 1. Avian Influenza Facts
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Date: Saturday, July 20, 2024, 10:50 AM


  1. Source and Transmission
  2. Agent Characteristics
  3. Virus Survival
  4. Clinical Signs in Birds

Learning Objective

At the end of this first section, we hope that you understand the basics of the avian influenza virus and signs of infection. 

We also hope that you learn and understand some facts about "Bird Flu" and its effects around the world.

What is Avian Influenza?

Avian is another word for bird.

, or flu, is a type of virus that causes disease in many different animals and people. A virus is a tiny germ that replicates, or copies itself, inside living cells.
  • Avian influenza, or AI, is caused by type A influenza virus.
  • The avian flu virus is different from the flu virus that normally makes people sick.

Influenza Virus
CDC Image Library: Cynthia Goldsmith

Who Gets Avian Influenza?

  • Avian influenza (AI) virus must find and enter a living animal so it can survive and multiply. This animal is called a host.1,6
  • Many different animals can be hosts for avian influenza, however, birds are the most likely to become infected.
  • Over 60 different species of backyard, wild, and pet birds may be affected by avian influenza.

  • Domesticated poultry are birds that you may keep in your backyard, such as chickens, ducks, quails, pheasants, guinea fowl and turkeys. They have the highest risk of infection and death from avian influenza.

  • AI virus is carried in the digestive tract of wild migratory waterfowl such as geese, ducks, and shorebirds. These migratory birds are the natural reservoir for the avian influenza virus and can spread the virus to other birds.

Avian Influenza HostsAI Host Transmission
Figure Credit: Dr. Daniel Perez


Avian Influenza Transmission

Routes of Transmission

How do birds get avian influenza?

  • Avian influenza is transmitted, or spread, in many different ways.1,6

  • Infected birds spread the influenza virus in their saliva (spit), nasal secretions (snot), and feces (poop).

  • Birds become infected with avian influenza through contact with infected birds, or through contact with contaminated materials such as soil, cages, feed and water.

  • Rodents and insects may also carry the virus on their body.

  • Vehicles and equipment can transport the virus to your backyard and birds as well.


Virus Characteristics

There are many different avian influenza viruses. The virus can be identified in two ways: the subtype and the category. 1,6


Subtypes are identified in a lab based on two proteins found on the outside of the virus virus called hemagglutinin (H) and neuraminidase (N).
  • Hemagglutinin (H) proteins are responsible for binding the virus to the cell that is being infected. There are 16 H subtypes. (H1-H16) H5 and H7 commonly infect poultry.
  • Neuraminidase (N) proteins help the virus get into a host cell. There are 9 N subtypes. (N1-N9)

Birds can carry 144 possible combinations of influenza A subtypes. One very commonly occurring subtype is H5N1.

Avian Influenza VirusAI structure CDC
Adapted from CDC Image Library: Dan Higgins

AI is classified into two categories, Low Pathogenic Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI) based on how sick the bird looks.

  • LPAI - Is the most common form of AI. Signs of disease range from none ,to ruffled feathers and a decrease in egg production. Subtypes LPAI H5 and H7 are carefully watched since these virus subtypes can mutate into a high pathogenic form.
  • HPAI - Is less common, but spreads rapidly in poultry flocks, causing severe illness, and can kill 90 - 100% of infected birds within 48 hours of exposure.

Signs of AI in Birds

Once a bird is infected, it usually takes 1-10 days before signs appear. That infected bird can spread the virus for up to 21 days to other birds. The best way to prevent the spread of disease is to know the signs of avian influenza and to respond quickly. 3

Birds may have a variety of different signs:

  • Inactivity, ruffled feathers, poor appetite, diarrhea

  • Decreased egg production, soft-shells or misshapen eggs

  • Swelling of the head, eyelids, comb, wattles and hocks

  • Cyanosis (dark blue color) of wattles, combs, and legs

  • Coughing, sneezing, nasal discharge

  • Sudden death

Comb Discoloration
Comb Cyanosis

Swollen Wattles
Swollen Wattles

These signs are similar to other poultry diseases, such as Exotic Newcastle Disease. Contact your local 4-H, county extension agent, or local/state veterinarian for immediate assistance if you observe signs of disease in your birds.

Virus Survival

Influenza virus
CDC Photo Library: Erskine Palmer

Avian influenza virus can survive outside of a host for long periods of time.19

  • The virus can live for up to one month in a poultry house setting at 40ºF.
  • AI virus has also been found to survive in lakes (where waterfowl usually gather) for over 30 days at freezing temperatures.

It is important to practice proper decontamination and disposal of litter, manure, and other wastes as the virus can linger on surfaces and in water.

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