Bird flu, also known as avian influenza, is a viral infection that can infect birds and some mammals. There are many different strains of bird flu viruses that vary in how severe they are and how easily they can spread between birds and other animals. The most well-known bird flu strain, H5N1, is highly pathogenic and has caused major outbreaks in domestic poultry and wild birds around the world.
What is bird flu?
Bird flu is caused by influenza type A viruses that infect birds. There are many different subtypes of the virus, classified based on two proteins on the surface of the virus – hemagglutinin (H) and neuraminidase (N). Some bird flu viruses, such as the H5N1 strain, are highly pathogenic, meaning they cause severe disease and death in infected birds. Other strains, such as H7N9, cause milder symptoms but can still spread rapidly through bird populations.
Wild aquatic birds, such as ducks and geese, are the natural reservoir for avian influenza viruses. These birds often do not get sick from the viruses they carry. However, domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal influenza.
Bird flu viruses do not usually infect humans, but some strains like H5N1 and H7N9 have caused human infections and deaths. Transmission to humans occurs through direct contact with infected birds or contaminated environments. There is concern that bird flu viruses could mutate and gain the ability for human-to-human transmission, sparking a pandemic.
Bird flu outbreaks in Colorado
There have been several notable outbreaks of bird flu in Colorado in wild birds and poultry flocks:
- In 2022, a highly pathogenic H5N1 outbreak in a commercial egg laying facility resulted in the death of 1.36 million chickens. This was the first confirmed case of H5N1 infection in commercial poultry in the United States since 2022.
- In March 2022, H5N1 was detected in captive wild birds, including a snowy owl, at the Colorado Raptor Center in Fort Collins. The disease spread rapidly through the facility, killing almost all of the 50 raptors living there.
- In 2015, a backyard poultry flock in Mesa County, Colorado was infected with H7N9, resulting in the culling of about 100 chickens. This was the first and only known case of H7N9 in the U.S.
- Between 2014-2015, H5N8 outbreaks in a backyard flock and at multiple captive wildlife facilities led to the deaths of thousands of wild birds. Bald eagles, snowy owls, and vultures were among the affected species.
The 2022 H5N1 event was the largest known outbreak of highly pathogenic bird flu in the U.S. to date. The rapid spread across the commercial facility highlights how transmissible the virus can be between birds in confined housing conditions.
What wild birds have tested positive for bird flu in Colorado?
Several species of wild birds have tested positive for avian influenza during outbreaks in Colorado:
| Bird Species | Bird Flu Strain |
|---|---|
| Snowy owl | H5N1 |
| Bald eagle | H5N8 |
| Turkey vulture | H5N8 |
| Canada goose | H5N1, H5N2 |
| Duck | H5N1 |
| Gull | H5N1 |
| Hawk | H5N1 |
| Falcon | H5N1 |
Waterfowl like geese and ducks and raptors like hawks, falcons, and bald eagles seem especially impacted by bird flu in Colorado. However, the virus has been detected in many other wild bird species during routine surveillance sampling. Backyard bird species like finches, sparrows, and robins have also occasionally tested positive.
What areas have been affected by bird flu in Colorado?
Here are the major regions in Colorado that have had confirmed cases of bird flu in wild birds and poultry flocks:
- Northeast Colorado: Morgan, Logan, Phillips, Sedgwick, Washington, Yuma, and Lincoln counties. Includes the 2022 H5N1 outbreak in a commercial facility.
- Northern Colorado: Larimer and Weld counties. Includes the 2022 H5N1 event in captive raptors at the Colorado Raptor Center.
- Western Slope: Mesa county. Location of the 2015 H7N9 infection in a backyard flock.
- Denver metro area: Adams, Arapahoe, Denver, Douglas, and Jefferson counties. Positive samples detected through routine surveillance.
The pattern of spread often follows major migratory flyways across the state. Birds congregating along rivers, lakes, and wetlands facilitate viral transmission between wild waterfowl and other species. Urban and suburban areas also see cases in backyard flocks and captive birds.
How are bird flu outbreaks monitored in Colorado?
Monitoring and early detection of bird flu in Colorado involves several key strategies:
- Routine surveillance of wild migratory birds. Federal and state agencies coordinate collections of samples from live and hunter-harvested wild birds.
- Testing of sick or dead birds. Members of the public are encouraged to report dead wild birds for testing.
- Outbreak investigation and tracing. Rapid response to confirm outbreaks, identify affected birds, and implement quarantine and culling measures as needed.
- Cooperation with poultry producers. Commercial and backyard flock owners are encouraged to monitor for unusual bird illnesses and deaths and report sick birds for testing.
- Public education campaigns to raise awareness of the signs of bird flu and remind people to avoid contact with wild birds.
Various federal, state, and local agencies are involved in bird flu surveillance in Colorado, including USDA Wildlife Services, Colorado Parks and Wildlife, public health departments, and Colorado’s state veterinarian’s office.
What precautions should you take regarding bird flu in Colorado?
Although human infections are very rare, here are some recommended precautions from public health authorities when bird flu is circulating:
- Avoid direct unprotected contact with wild birds. Do not handle sick or dead birds with bare hands.
- Keep backyard poultry away from wild waterfowl. Restrict their outdoor access in affected areas.
- Cook poultry products thoroughly to an internal temperature of 165°F to kill any potential viruses.
- Report any unusual sickness or death among backyard or commercial poultry flocks.
- Seek medical care immediately if you have flu symptoms after contact with infected birds.
Hunters should take routine precautions when handling game birds, like wearing gloves, washing hands, and fully cooking meat. The risk to the general public remains very low during a bird flu outbreak.
Conclusion
Bird flu is an ongoing concern for both wild bird populations and domestic poultry in Colorado. Major outbreaks have occurred in recent years impacting backyard and commercial flocks. Surveillance and biosecurity measures continue to be important to detect cases early and limit spread. Several wild bird species have tested positive, but waterfowl, raptors, and scavenging birds appear most affected. With proper precautions, the risk to humans remains minimal during an outbreak.
