Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in wild birds the United States, by county, 2021-2025. Updated February 10, 2025.
How is avian influenza spread?
Avian influenza is spread when wild and domestic birds shed the virus into the environment through their oral and nasal secretions as well as excrement. Following the 2015 avian influenza outbreak, USGS, USDA, and other partners confirmed through data on wild bird migratory patterns—including intercontinental movements and genetic analyses of viral strains—that the global spread of HPAI has been driven in large part by migratory waterfowl.
The 2015 HPAI outbreak was associated with movement of migratory birds from the East Asian-Australasian flyway to Western North America. The 2021 North American HPAI outbreak that started in Canada was associated with Transatlantic movement of migratory waterfowl to Eastern North America (but there were also several western introductions).
Learn more: USGS science on avian influenza
Related
Can people get avian influenza?
While rare, human infections with avian influenza viruses have occurred. The Centers for Disease Control (CDC) consider the risk to the general public from infections to be low. There have been human cases associated with the dairy cattle and wild bird strains of HPAI. To date, most human cases have been associated with farm workers (poultry and dairy cattle operations) as well as people who have...
Can wild birds spread avian influenza to domestic poultry?
Wild birds can directly or indirectly spread avian influenza to domestic poultry. The indirect route is likely most common due to viral contamination of the farm environment (feed, equipment, boots, clothes). The U.S. Department of Agriculture has found that farm-to-farm movement is also a major route for avian influenza spread, noting that farm biosecurity is critical to reduce the risk of avian...
How do scientists know if individual wild birds are infected with avian influenza?
The U.S. Department of Agriculture implements a plan every year to monitor wild birds for highly pathogenic avian influenza. This national plan could not be implemented without the engagement of State partners, the National Flyway Council, the Department of the Interior, and other agencies. This coordinated effort is revised annually based on new science and data shared through the Interagency...
What are the different types of avian influenza? What do the numbers next to H and N mean?
Avian influenza (AI) type A viruses are divided into subtypes based on two proteins on the surface of the virus: Hemagglutinin (HA), of which there are 16 subtypes (H1-H16). Neuraminidase (NA), of which there are 9 subtypes (N1-N9). Many combinations of HA and NA proteins are possible, for example H5N1, H5N2, H7N2, and H7N8. AI viruses are also classified into two groups based on their ability to...
What is chronic wasting disease?
Chronic wasting disease (CWD) is a fatal, neurological illness occurring in North American cervids (members of the deer family), including white-tailed deer, mule deer, elk, and moose. Since its discovery in 1967, CWD has spread geographically and increased in prevalence locally. CWD is contagious; it can be transmitted freely within and among cervid populations. No treatments or vaccines are...
What is White-nose Syndrome?
White-nose syndrome is an emergent disease of hibernating bats that has spread from the northeastern to the central United States at an alarming rate. Since the winter of 2007-2008, millions of insect-eating bats in at least 40 states and eight Canadian provinces have died from this devastating disease. The disease is named for the white fungus, Pseudogymnoascus destructans, that infects skin of...
Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in North America, 2021-2025
Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in wild birds the United States, by county, 2021-2025. Updated February 10, 2025.
Avian Influenza Transmission Risk Model Web Application Virtual Tour
The Avian Influenza Transmission Risk Model web application depicts the intricate connections between 16 layers of administrative, environmental, and economic data in an application that runs inside a web browser. To view and manipulate the full web application, please visit http://www.pwrc.usgs.gov/ai.
The Avian Influenza Transmission Risk Model web application depicts the intricate connections between 16 layers of administrative, environmental, and economic data in an application that runs inside a web browser. To view and manipulate the full web application, please visit http://www.pwrc.usgs.gov/ai.
Blue-winged teal in Texas. Inset shows avian influenza virus
Blue-winged teal in Texas. Inset shows avian influenza virus
Blue-winged teal in Texas. Inset shows avian influenza virus
Sampling Forster’s Tern Chicks for Avian Influenza Study
Scientists sampling Forster's Tern chicks for avain influenza during salt pond restoration work in south San Francisco Bay salt ponds.
Scientists sampling Forster's Tern chicks for avain influenza during salt pond restoration work in south San Francisco Bay salt ponds.
Releasing Forster’s Tern Chicks after Sampling for Avian Flu
Scientists prepare to release Forster's Tern chicks following sampling for avian influenza study.
Scientists prepare to release Forster's Tern chicks following sampling for avian influenza study.
What are the differences between low pathogenic and highly pathogenic avian influenza viruses and how are influenza viruses grouped?
linkListen to hear the answer.
Testing for Avian Influenza
A USGS scientist takes a sample from a northern pintail duck (Anas acuta) to be tested for avian influenza.
A USGS scientist takes a sample from a northern pintail duck (Anas acuta) to be tested for avian influenza.
USGS biologists swab a hen mallard duck for avian influenza
USGS biologists swab a hen mallard duck for avian influenza in Rio Grande County, Colorado.
USGS biologists swab a hen mallard duck for avian influenza in Rio Grande County, Colorado.
Related
Can people get avian influenza?
While rare, human infections with avian influenza viruses have occurred. The Centers for Disease Control (CDC) consider the risk to the general public from infections to be low. There have been human cases associated with the dairy cattle and wild bird strains of HPAI. To date, most human cases have been associated with farm workers (poultry and dairy cattle operations) as well as people who have...
Can wild birds spread avian influenza to domestic poultry?
Wild birds can directly or indirectly spread avian influenza to domestic poultry. The indirect route is likely most common due to viral contamination of the farm environment (feed, equipment, boots, clothes). The U.S. Department of Agriculture has found that farm-to-farm movement is also a major route for avian influenza spread, noting that farm biosecurity is critical to reduce the risk of avian...
How do scientists know if individual wild birds are infected with avian influenza?
The U.S. Department of Agriculture implements a plan every year to monitor wild birds for highly pathogenic avian influenza. This national plan could not be implemented without the engagement of State partners, the National Flyway Council, the Department of the Interior, and other agencies. This coordinated effort is revised annually based on new science and data shared through the Interagency...
What are the different types of avian influenza? What do the numbers next to H and N mean?
Avian influenza (AI) type A viruses are divided into subtypes based on two proteins on the surface of the virus: Hemagglutinin (HA), of which there are 16 subtypes (H1-H16). Neuraminidase (NA), of which there are 9 subtypes (N1-N9). Many combinations of HA and NA proteins are possible, for example H5N1, H5N2, H7N2, and H7N8. AI viruses are also classified into two groups based on their ability to...
What is chronic wasting disease?
Chronic wasting disease (CWD) is a fatal, neurological illness occurring in North American cervids (members of the deer family), including white-tailed deer, mule deer, elk, and moose. Since its discovery in 1967, CWD has spread geographically and increased in prevalence locally. CWD is contagious; it can be transmitted freely within and among cervid populations. No treatments or vaccines are...
What is White-nose Syndrome?
White-nose syndrome is an emergent disease of hibernating bats that has spread from the northeastern to the central United States at an alarming rate. Since the winter of 2007-2008, millions of insect-eating bats in at least 40 states and eight Canadian provinces have died from this devastating disease. The disease is named for the white fungus, Pseudogymnoascus destructans, that infects skin of...
Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in North America, 2021-2025
Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in wild birds the United States, by county, 2021-2025. Updated February 10, 2025.
Distribution of Highly Pathogenic Avian Influenza H5 and H5N1 in wild birds the United States, by county, 2021-2025. Updated February 10, 2025.
Avian Influenza Transmission Risk Model Web Application Virtual Tour
The Avian Influenza Transmission Risk Model web application depicts the intricate connections between 16 layers of administrative, environmental, and economic data in an application that runs inside a web browser. To view and manipulate the full web application, please visit http://www.pwrc.usgs.gov/ai.
The Avian Influenza Transmission Risk Model web application depicts the intricate connections between 16 layers of administrative, environmental, and economic data in an application that runs inside a web browser. To view and manipulate the full web application, please visit http://www.pwrc.usgs.gov/ai.
Blue-winged teal in Texas. Inset shows avian influenza virus
Blue-winged teal in Texas. Inset shows avian influenza virus
Blue-winged teal in Texas. Inset shows avian influenza virus
Sampling Forster’s Tern Chicks for Avian Influenza Study
Scientists sampling Forster's Tern chicks for avain influenza during salt pond restoration work in south San Francisco Bay salt ponds.
Scientists sampling Forster's Tern chicks for avain influenza during salt pond restoration work in south San Francisco Bay salt ponds.
Releasing Forster’s Tern Chicks after Sampling for Avian Flu
Scientists prepare to release Forster's Tern chicks following sampling for avian influenza study.
Scientists prepare to release Forster's Tern chicks following sampling for avian influenza study.
What are the differences between low pathogenic and highly pathogenic avian influenza viruses and how are influenza viruses grouped?
linkListen to hear the answer.
Testing for Avian Influenza
A USGS scientist takes a sample from a northern pintail duck (Anas acuta) to be tested for avian influenza.
A USGS scientist takes a sample from a northern pintail duck (Anas acuta) to be tested for avian influenza.
USGS biologists swab a hen mallard duck for avian influenza
USGS biologists swab a hen mallard duck for avian influenza in Rio Grande County, Colorado.
USGS biologists swab a hen mallard duck for avian influenza in Rio Grande County, Colorado.
Updated Date: April 17, 2025