#19,040
After several months of relatively low numbers of commercial poultry affected by HPAI H5N1 in the United States, in the last week of January two major outbreaks (in Colorado and Pennsylvania) were reported to the USDA.
While there were vague reports on the Weld County outbreak over the weekend, yesterday the Colorado Department of Agriculture (CDA) released the following statement.
Avian Influenza Detected in Commercial Egg-Layer Facility in Weld County
Monday, February 2, 2026
This January, the Colorado Department of Agriculture (CDA) has confirmed three new detections of Highly Pathogenic Avian Influenza (HPAI) in backyard flocks in Larimer and Logan Counties and one detection in a commercial egg layer operation in Weld County. All premises are currently under quarantine orders and control areas have been set up in Weld and Logan counties.
“The confirmation of these new HPAI cases is a reminder that the virus is actively circulating in our state,” said Dr. Maggie Baldwin, Colorado State Veterinarian. “We urge all flock owners to remain highly vigilant, monitor their birds closely for any signs of illness, and, most critically, to immediately reinforce and practice strict biosecurity measures to protect their flocks.”
Summary of New CasesLarimer 07: On January 5, 2026, CDA was notified of death losses in a backyard mixed species flock of 16 birds in Larimer County. Samples tested presumptive positive on January 6 and were confirmed by USDA's National Veterinary Services Laboratory on January 7.
Logan 01: On January 8, 2026, USDA was notified of a poultry chicken flock in Logan County experiencing increased death rates. Samples tested presumptive positive on January 9 and were confirmed on January 14. A total of 55 birds were lost. An area quarantine has been established for this premise and poultry owners within the quarantine area are asked to report the status of their flocks through an online self-reporting form.
Larimer 08: On January 9, 2026, CDA was notified of increased death losses in a backyard facility in Larimer County. The flock lost 18 birds (chickens and ducks). Samples tested presumptive positive on January 9 and were confirmed on January 14.
Weld 18: On January 28, CDA received notification of a mortality event in a commercial egg laying facility in Weld County which houses 1.33 million chickens. Samples tested presumptive positive on January 29 at the Colorado State University Veterinary Diagnostic Laboratory and were confirmed late on Friday, January 30, by the USDA’s National Veterinary Services Laboratory (NVSL).
A control area has been established for this premise (which is under a quarantine order) and poultry owners within the quarantine area are asked to report the status of their flocks through an online self-reporting form. The response for this facility is ongoing and is currently in the depopulation and disposal phase.
An updated Situation Report (#82 from January 30, 2026), which summarizes all HPAI detections in Colorado, can be found on the CDA landing page at ag.colorado.gov/HPAIresponse.
General Information on HPAI
HPAI is a viral disease that can cause severe illness and death in poultry. The recent detections signal that the virus is circulating, often carried by migrating wild birds which act as a reservoir for the disease. Colorado has been working proactively on HPAI response and testing, which has been incredibly successful at slowing the spread of avian influenza in the state. Since the summer of 2024, Colorado has not had any human cases of HPAI.
What Flock Owners Can Do: Biosecurity and Vigilance
The Colorado Department of Agriculture urges all livestock and poultry owners to remain vigilant and monitor their animals for symptoms of disease. The most critical step poultry owners can take is to implement strict biosecurity measures to protect their flocks.
Flock owners should:
Implement Biosecurity: Review and implement strong biosecurity measures, such as securing the flock from wild birds, especially waterfowl. The CDA has additional guidance available on their website at ag.colorado.gov/animal-health/biosecurity-101.
Monitor Animals: Watch for symptoms of illness, including sudden death, a drop in egg production, decreased food/water consumption, and lethargy.
Suspected HPAI Reporting
A delay in reporting can lead to a delay in necessary response measures which can compromise human and animal health.Poultry and Livestock: HPAI in poultry, dairy cattle, or other livestock species must be reported directly to the State Veterinarian’s Office. Information can be found on the CDA Reportable Diseases page.
Feline Cases: Suspected HPAI feline cases can be reported to the Colorado Department of Public Health and Environment (CDPHE) at 303-692-2700, and they will share that information with CDA.
Wild Birds: The public is urged to avoid contact with sick or dead wildlife without proper personal protective equipment (PPE) and to contact their local CPW office to report suspect cases of sick or dying wild birds.
For more information on HPAI, please see the CDA HPAI landing page.
Although the recent reduction in large commercial outbreaks may be a testament to better biosecurity practices, it may also have something to do with recent changes to the clade 2.3.4.4b virus.
Recent studies have indicated a shift in the N1 Neuraminidase stalk domain of H5N1 since 2022 which may decrease its transmissibility and virulence in poultry (see mBio Clade 2.3.4.4b H5N1 neuraminidase has a long stalk, which is in contrast to most highly pathogenic H5N1 viruses circulating between 2002 and 2020 by Enikő Hermann & Florian Krammer.)
The authors of the above report explain:
While the truncated version of the N1 neuraminidase stalk domain may be associated with increased virulence in poultry, the long version of the stalk domain has been associated with increased transmissibility in mammals.
The vast majority of highly pathogenic H5N1 of clade 2.3.4.4b that is currently circulating globally features the long stalk version of the neuraminidase, which may increase the risk for these viruses to become human-to-human transmissible.
While somewhat encouraging for the poultry industry, this change may prove less so the mammalian set, who could find themselves more susceptible to infection.
A reminder that HPAI H5N1 continues to change, and what we say about it today may not hold true tomorrow.
