As the current strain of bird flu has spread globally over the last several years, it has developed
multiple genetic mutations to spread beyond birds to infect a wider range of mammals in
the United States. The virus, also called H5N1 or avian flu, is a serious public health
threat that requires a wide range of expertise to track and predict. Earlier strains of
the virus were primarily only found in southeast Asia and were highly fatal to humans.
The Health Observatory works closely with researchers across Arizona’s university
system and public health departments to better understand the virus and bring reliable
health information to all Arizonans.
Members of the Health Observatory have more than 100 years of combined expertise
in public health work, including predictive modeling of infectious diseases. The team is
composed of current and former public health professionals, epidemiologists,
mathematicians and data modelers.
In early 2025, the Health Observatory formed the Arizona Union for Pathogenic Avian
Influenza Research. The group’s goal is to enhance communication, collaboration,
data sharing and response efforts with research partners, local and state public health
organizations, and animal health agencies.
National bird flu timeline
January 2022
First bird flu infection in a wild bird in the United States since 2016
February 2022
USDA announces bird flu outbreak in turkey from commercial poultry facility
April 2022
First reported human infection in the United States following close contact with an infected flock from Colorado
May 2022
First mammalian detection of bird flu in the United States
June-July 2022
Continued detection of bird flu infection in a variety of mammalian species
March 2024
First confirmed cases of bird flu infection in dairy cattle from Kansas and Texas
How bird flu spread to cows and humans
For a couple of years after first arriving in the United States, bird flu infections circulated among birds and some wildlife. In June 2022, the Arizona Game and Fish Department first identified bird flu in wild birds. The virus did not infect people during that time.
However, in early 2024, a strain of bird flu known as B3.13 was identified in dairy cattle in Texas and Michigan. The virus had mutated and was now able to infect cattle and other mammals for the first time; this is known as a “spillover event.”
This new strain also caused a “spillback event,” which meant that the newly infected cattle were now capable of spreading the B3.13 strain of the virus back to birds and wildlife. “Spillover” and “spillback” events where the virus reinfects previous hosts are some of the ways viruses evolve.
In late 2024, testing in Nevada confirmed another bird flu strain called D1.1 had made a jump into dairy cattle. This strain was originally found in wild birds and domestic poultry. This new jump was discovered when dairy milk in Nevada tested positive for bird flu.
This new strain caused further spillover events in which infected dairy cattle spread bird flu infections to humans. A dairy worker in the area tested positive for bird flu and had mild symptoms of infection. Several other people in Louisiana and British Columbia, Canada, also tested positive for this new strain of bird flu and showed signs of more severe illness.
Studying the genetics of the bird flu virus
Through genomic analysis conducted by Professor Mike Worobey from the University of
Arizona in 2024, we know that the virus spread from wild birds into cattle.
The B3.13 genotype is a new strain adapted to cows. It primarily affects dairy cows but
can also cause occasional infections in poultry and humans in the United States.
Genomic data also suggests that bird flu transmission in cattle is extensive enough to
cause outbreaks in other animals.
Read Worobey’s two-part report on the genetic epidemiology of the B3.13 bird flu strain.
- Part one includes background, data, methods and some of the research findings. Read part 1.
- Part two contains the rest of the findings, concluding remarks, acknowledgements and references. Read part 2.
Impact of bird flu in Arizona
Since it was identified in Arizona in June 2022, the bird flu virus has been detected in 25
different species. These include wild birds, zoo animals and one wild rodent species.
In late 2024, Arizona reported its first:
- Confirmed human cases, which were mild
- Commercial poultry operation outbreak
- Confirmed detection in wastewater
- Zoo mammal cases and deaths
In February 2025, testing of milk from one Arizona dairy farm identified the first
incidence of bird flu in Arizona cattle. Since then, a total of four dairy farms have been
reportedly affected in Arizona.
Arizona bird flu timeline
June 2022
First detection of bird flu in wild birds in Arizona
October 2022
14 pelicans from the Phoenix Zoo die of H5N1 infection following acute neurologic signs and seizures
November 2022
First Arizona backyard flock detection of bird flu in Yavapai County
March – April 2023
21 California Condors from the Arizona-Utah flock die of bird flu infection.
December 2023
First Arizona mammalian detection of bird flu in an Abert’s Squirrel in Navajo County.
November 2023
First Arizona commercial poultry detection in Pinal County. Backyard flock detection of the same strain in Maricopa County.
December 2024
First detection in Arizona zoo mammals and in wastewater from multiple cities.
February 2025
First milk from an Arizona dairy farm was found to be contaminated.
Bird flu strikes Arizona–Utah California condor flock
The Peregrine Fund, which manages the Arizona-Utah flock of California condors,
observed several sick and dead birds in spring 2023. Between March and May, bird flu
was confirmed as the cause of death in more than 20 birds.
In August 2023, the U.S. Fish and Wildlife Service’s Incident Command Team, in
collaboration with other partners, conducted a vaccine trial on three groups of California
condors. Results showed that the vaccine may reduce the severity of infection and
minimize the likelihood of death. As of February 2024, 94 birds have received at least
one dose of the vaccine.
The Arizona–Utah population moves throughout northern Arizona and southern Utah, using the
landscape within Grand Canyon National Park, Zion National Park, Vermillion Cliffs National
Monument, the Kaibab Plateau and surrounding areas.
Arizona detects bird flu in wastewater
Bird flu was confirmed in wastewater in Flagstaff, part of Coconino County, as well as
Phoenix, Surprise and Tempe in Maricopa County in December 2024.
TGen also identified the presence of chicken and wild bird DNA in these samples,
indicating that chickens and birds may be a source of the bird flu virus in the wastewater.
Spillover to Arizona zoo animals
In December 2024, the Wildlife World Zoo and Maricopa County Department of Public
Health reported bird flu infections in several of the zoo’s animals. Five animals died,
including a cheetah, a mountain lion, a swamphen, an Andean goose and a
Kookaburra. A white tiger also tested positive for the virus.
Several other wild bird species have also been impacted by the virus at zoologic
institutions in Arizona. Previously, in October 2022, 14 pink-backed pelicans at the
Phoenix Zoo died of bird flu infections following severe neurologic signs and seizures.
Arizona research community responses to bird flu outbreak
Health Observatory partner TGen North is engaged in the bird flu response
through several focus areas:
- Agency consultations with local, state and tribal public health and animal health partners. Partners include the Arizona Game and Fish Department, the Department of Health,
the Department of Agriculture, and Maricopa and Coconino counties. - Animal surveillance in zoos, wildlife and companion animals. TGen established collaborations with the Reid Park Zoo in Tucson and Bearizona Wildlife Park in Williams to proactively monitor for avian flu.
- Sample testing development and validation for wildlife and environmental testing.
- Safety systems for handling the virus.
- Communications efforts in partnership with the ASU Health Observatory.
- Environmental screening in natural waterways and parks.
- Wastewater surveillance in Maricopa and Coconino counties.
Want to know more about bird flu?
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Thank you to the TGen North team, particularly Hayley Yaglom, for helping to develop content for this site.