Section 1. Avian Influenza Facts

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Course: Avian Influenza Biosecurity for Backyard Flock Owners
Book: Section 1. Avian Influenza Facts
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Date: Sunday, June 23, 2024, 10:41 PM


  1. Source and Transmission
  2. Agent Characteristics
  3. Virus Survival
  4. Clinical Signs in Birds
  5. HPAI H5N1
  6. Human Concerns

An Introduction to Avian Influenza

By the end of this section you should
  •  Understand the basics of the avian influenza virus,
  •  Know virus subtypes and categories, and
  •  Recognize clinical signs of the virus.
Special topics review the highly pathogenic subtype H5N1 and human concerns during an outbreak.

Avian influenza (AI) outbreaks occur sporadically throughout the world and are of great importance to animal and human health. This disease is very disruptive to the poultry industry, causing millions of chickens, turkeys, and other poultry to be destroyed to prevent further spread of the disease. There is a growing concern over the loss of human lives and management of potential pandemics of the highly pathogenic strains of the avian influenza virus.

In the following chapters you will learn more about avian influenza, prevention measures, response procedures, and recovery from an outbreak.

Geese | Photo Credit: Jenny Madsen
Photo Credit: Jenny Madsen

Source and Transmission

What is avian influenza?
  • Avian influenza (AI) is an infectious disease caused by type A influenza virus. There are three types of influenza virus: A, B, and C.1,6
  • All influenza viruses affecting domestic animals (horses, pigs, poultry, etc.) belong to type A, which is also responsible for causing the most serious epidemics in humans. Influenza types B and C mainly affect humans.
  • AI virus is carried in the intestines of wild migratory waterfowl such as geese, ducks, and shorebirds. These birds are a natural reservoir for type A influenza because the virus generally does not cause disease in these species.

Which birds are susceptible to AI infection?
  • More than 60 different species of domestic, wild, and pet birds may be affected by avian influenza.
  • However, domesticated poultry, such as chickens, ducks, quails, pheasants, guinea fowl and turkeys are highly susceptible to infection.

AI Reservoir and Host Transmission
AI Host Transmission
Figure Credit: Dr. Daniel Perez

How do birds get avian influenza?

  • Infected birds shed the influenza virus in their saliva, nasal secretions, and feces.
  • Birds may become infected with avian influenza virus through direct contact with contagious waterfowl or other infected poultry, or through indirect contact with contaminated surfaces such as dirt, cages, or materials like feed and water.
  • Rodents and insects may also physically carry the virus around coops.

CDC Image Library: Cynthia Goldsmith

Virus Characteristics

There are many different avian influenza (AI) viruses and they are characterized into subtypes based on two proteins found on the virus called hemagglutinin (H) and neuraminidase (N). 1,6
  • Hemagglutinin (H) proteins are responsible for binding the virus to the cell that is being infected. There are 16 H subtypes. (H1 to H16)
  • Neuraminidase (N) proteins help the virus get into a host cell. There are 9 N subtypes. (N1 to N9)
Birds can carry 144 possible combinations of influenza A subtypes. One very commonly occurring subtype is H5N1.

AI structure CDC
Adapted from CDC Image Library: Dan Higgins


AI is also classified into two categories, Low Pathogenic Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI) based on the severity of the disease they cause.

  • 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 monitored as they have been known to mutate into HPAI.
  • 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. 

Virus Survival

CDC Photo Library: Erskine Palmer

Avian influenza (AI) virus can survive outside a host for long periods depending on temperature and humidity of the environment.

The virus can live for up to one month inside a poultry house at 40 ºF.

AI virus has also been found to survive in lakes (where waterfowl usually congregate) for over 30 days at freezing temperatures.

It is important to undergo proper cleaning, decontamination, and disposal of litter, manure, and other contaminated products as the virus can linger on surfaces and in water.

AI is inactivated when heated to 158ºF for 1 hour or by exposure to disinfectants or extreme pH levels.

Signs of AI in Birds

Once a bird is infected, it usually takes 1-10 days before signs appear. That infected bird can shed 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

Bird Flu - Highly Pathogenic Avian Influenza (HPAI) H5N1

Bird flu is often used synonymously with avian influenza (AI), however, bird flu specifically refers to the HPAI H5N1 strain that has killed millions of birds. HPAI H5N1 is also one of the few avian influenza viruses that has crossed the species barrier and infected humans. Emerging from Hong Kong in 1997, it has caused the largest number of confirmed cases of severe disease and death in humans from an AI virus.2

More than 800 human infections with Asian HPAI H5N1 viruses have been reported to WHO from primarily 16 countries in Asia, Africa, the Pacific, Europe, and the Near East since November 2003.  Indonesia, Vietnam, and Egypt have reported the highest number of human HPAI Asian H5N1 cases to date.4 

HPAI Asian H5N1 has not been reported in the United States, however, it is possible that bird flu could enter the country via migratory birds. In order for H5N1 to enter the United States, infected wild birds from Asia or West Africa would have to survive the disease and carry it to breeding grounds in the Pacific Islands, Alaska, or Canada. The virus would then have to pass to another species that migrates to the continental United States.6

Ninety-nine percent of North American migratory waterfowl do not come from Europe, Asia, or Africa where the virus has been found. Scientists continue to test a representative sample of birds in Alaska and Canada and along major flyways in the continental United States in an effort to detect whether avian influenza has arrived via these routes. HPAI H5N1 has not been detected along major flyways in the continental United States.  

Avian Influenza Outbreaks in the U.S.

While HPAI H5N1 has not been reported in the U.S. as of February 2011, outbreaks of other HPAI subtypes have occurred throughout the country.

To date, there have been four outbreaks in the U.S. of HPAI occurring in 1924, 1983, 2004, and 2014. Several low pathogenic outbreaks have resulted in mass depopulations of poultry as well. Many of these cases are believed to have resulted from contact with AI-infected live bird markets and sharing equipment between farms.2 

The 2014-2015 outbreak of high pathogenic avian influenza is the largest animal health emergency in US history. In less than six months, over 48 million birds on 223 premises were affected by the virus. The outbreak devastated the affected regions of the Pacific Northwest and Midwest. While the exact cause of the spread from farm to farm has yet to be determined, most experts agree that movement is a major factor. Because the virus can survive in the environment for long periods of time, the virus can be moved from farm to farm by people, animals, farm vehicles or other pieces of equipment. Because of this, biosecurity on individual farms is extremely important and it is imperative to always follow a strict management and health program. Biosecurity includes procedures that minimize risk of a virus or other infectious agent from entering a premise or facility.  The following video will provide tips to improve your personal biosecurity.

Documented HPAI in Poultry6,22
17 million
 2014-2015  USA  H5N2, H5N8, H5N1 49 million 

Documented LPAI in Poultry6,22
Various LPAI
1199 Farms
178 Farms
2 million (60 Farms)
4.7 million (197 Farms)
H7N2, H2N2

UNICEF: HPAI H5N1 in Indonesia

Can I Catch Avian Influenza From Sick Birds?

  • AI viruses generally do not cause disease in humans; however, cases of human infection have been reported.2
  • Most human infections resulted from direct contact with feces and fluids of infected poultry to the person's mucus membranes (e.g. eyes, nose, and mouth). For example, not washing your hands properly after handling infected poultry and then rubbing your eyes could potentially result in infection.
  • Transmission of AI virus from person to person is rare.
  • In the U.S., commercial poultry that have tested positive or have been exposed to avian influenza will not go to market. Even if poultry and eggs were contaminated with the virus, proper cooking would kill the virus. Use a food thermometer to make sure you cook poultry to a temperature of at least 165°F. Eggs should be fully cooked without any runny yolks.7
Photo Credit: Jenny Madsen

Protecting Yourself

Keep in mind that human AI infections are very rare and using everyday biosecurity precautions are the first step to prevention.
  • Use gloves when handling sick or dead birds (for greater protection wear goggles and face masks).
  • Avoid contact with droppings and do not touch your mouth or eyes with your hands while working. 
  • After handling sick or dead birds, change and launder your clothes and always wash your hands with soap and water or gel sanitizer when done.7
  • Get your seasonal flu shot. While the seasonal flu will not prevent AI infections, it will help prevent mutant variants from forming. For example, if you are infected with two different virus types, they could combine to produce a more infectious strain. Seasonal flu vaccines are inexpensive and offered at many local clinics and pharmacies generally from October to April.

In 2007, the Food and Drug Administration (FDA) approved an avian influenza vaccine against one strain of HPAI H5N1 for humans; however, it is not currently available to the public. In the event of a pandemic, the government will distribute the vaccine as needed.

Flu Vaccine
CDC Photo Library: Jim Gathany

Signs and Symptoms of AI in People

Due to the infrequent cases of avian influenza, definitive symptoms are difficult to determine. However, avian flu will probably begin like seasonal flu, with the severity of symptoms drastically increasing over the first 12-24 hours.6

Signs and Symptoms:
  • Influenza-like symptoms (e.g. fever, cough, sore throat, muscle aches)
  • Severe respiratory illness (e.g. pneumonia, acute respiratory distress)
  • Occasionally, nausea, diarrhea, vomiting and neurological changes are seen.

Notice that some of these signs and symptoms are very similar to those of seasonal cold and flu; however, if you develop a high fever or have difficulty breathing, seek medical attention immediately.

Laboratory tests are used to diagnose avian influenza infection in humans by swabbing the patient's nose or throat. Samples are then sent for diagnostic testing to verify the presence or absence of virus.7

If found to have avian influenza, you will be treated with antiviral medications such as oseltamivir (Tamiflu®) or zanamivir (Relenza®). Treatment strategy and drug effectiveness continue to be evaluated.

Wikipedia: Moriori