Avian influenza, commonly known as bird flu, is a viral infection that can infect not only birds but also humans and other mammals. Avian flu viruses occur naturally in wild birds, especially waterfowl like ducks and geese. These wild birds usually do not get sick from avian influenza viruses. However, avian flu infections in domestic poultry, including chickens, turkeys and ducks, can cause severe illness and death. Some forms of the virus are zoonotic, meaning they can spread from animals to humans and cause disease. When people do become infected, the mortality rate is about 60%. For these reasons, understanding what types of birds are most likely to transmit avian influenza is important for monitoring outbreaks and protecting human and animal health.
Wild Waterfowl as Natural Reservoirs
Wild waterfowl, like ducks, geese and swans, are considered to be natural reservoirs for avian influenza viruses. This means that these bird populations harbor influenza viruses in their intestines and respiratory tract and transmit the viruses among each other. However, wild waterfowl usually do not become ill from avian flu infections themselves. They have evolved to be resistant hosts where the viruses can persist without causing harm. Scientists posit that all known subtypes of influenza A viruses, including strains with pandemic potential, originally emanate from waterfowl reservoirs. For example, one study in Canada found that ducks and geese hosted at least 13 different subtypes of avian influenza while on their breeding grounds. Surveillance of wild waterfowl provides an opportunity to detect emerging avian flu strains before they spread to poultry flocks.
Key Facts About Waterfowl and Avian Flu
- Ducks and geese carry more avian influenza virus subtypes compared to other birds.
- The viruses replicate in their intestinal tract and are shed in high quantities in their feces.
- Migratory flyways allow viruses to spread great distances during seasonal migration.
- Year-round surveillance programs track avian flu strains in ducks and geese.
Domestic Poultry at High Risk
While avian influenza viruses do not typically cause significant disease in wild waterfowl, they can be highly pathogenic and deadly in domestic bird species like chickens and turkeys. The close quarters of commercial poultry farming, combined with the lack of prior virus exposure, facilitates rapid transmission and increased virulence of the virus in domestic flocks. Numerous outbreaks of highly pathogenic H5 and H7 influenza subtypes have occurred in poultry in recent decades, resulting in the culling of millions of infected birds to prevent further spread. Enhanced surveillance and biosecurity measures on poultry farms are critical to prevent future outbreaks.
Key Facts About Domestic Poultry and Avian Flu
- Chickens, turkeys and ducks are highly susceptible to disease from avian influenza infection.
- High mortality rates, up to 100%, can occur in commercial flocks during an outbreak.
- Strict quarantines and culling of infected flocks are necessary to control outbreaks.
- Good farm biosecurity helps prevent the virus spreading between flocks.
Backyard and Pet Birds Also at Risk
Backyard flocks and pet birds have also been impacted by avian influenza. Outbreaks in backyard poultry flocks have accompanied infections in commercial operations. Pet stores and zoos with bird exhibits have had to restrict access and monitor for illness due to avian flu outbreaks. Birds like parrots, parakeets and guinea fowl appear to be quite susceptible to infection and disease from some avian influenza viruses. Strong surveillance and tracking of backyard flocks and pet birds is important to control community-level spread.
Key Facts About Backyard and Pet Birds and Avian Flu
- Backyard chicken flocks are at risk when avian flu circulates in an area.
- Pet stores have had outbreaks requiring quarantine and closure.
- Parrots have died in large numbers during some avian flu outbreaks.
- Owners should know the signs of illness and report sick birds.
Wild Bird Species Implicated in Transmission
In addition to waterfowl like ducks and geese, a diversity of wild bird species have been affected by avian flu outbreaks and may contribute to transmission. For example, the widespread 2022 outbreak of H5N1 clade 2.3.4.4b avian influenza in North America caused mortality in many types of wild birds. Raptors like bald eagles, great horned owls and red-tailed hawks were among the species infected. This suggests that predators can become infected from consuming sick prey. Other impacted wild species have included crows, jays, gulls, herons and even small songbirds like finches. Monitoring wild bird populations remains crucial for tracking the spread of avian influenza viruses.
Key Facts About Other Wild Birds and Avian Flu
- Raptors are susceptible when they prey on infected waterfowl.
- Crows and jays are especially affected by H5N1 outbreaks.
- Seabirds like gulls can spread viruses between water sources.
- Songbirds may contribute to local spread of some strains.
Poultry, Pet and Wild Birds All Play a Role
In summary, avian influenza viruses can infect a wide diversity of avian species. However, some key trends have emerged in terms of birds that serve as natural reservoirs, those that are highly susceptible, and those that can contribute to transmission:
- Waterfowl like ducks and geese are natural reservoirs and vectors for various influenza subtypes.
- Domestic poultry flocks are at high risk of large outbreaks and severe disease.
- Backyard and pet birds are susceptible to spillover from commercial farms.
- Certain wild bird populations appear prone to infection during outbreaks.
Ongoing surveillance of waterfowl, poultry and wild birds is critical for monitoring the spread of avian influenza viruses with zoonotic potential. Biosecurity measures help limit transmission between flocks. Reports of unexplained illness and mortality in bird populations should be investigated swiftly. By understanding what birds are involved in disease spread, we can better implement interventions to protect human and animal health.
Reporting Avian Flu in Birds
Avian influenza outbreaks in domestic and wild birds must be reported quickly so that containment measures can be implemented without delay. Here are some key steps for reporting suspected avian flu:
- Poultry farmers should immediately report unusual illness or deaths in their flocks to veterinarians or agriculture authorities.
- Backyard flock owners should contact their state veterinarian if birds become sick or die suddenly.
- Pet bird owners should get in touch with an avian veterinarian if their bird exhibits flu-like symptoms.
- The public should report dead wild birds, especially waterfowl, to the state wildlife agency for testing.
- Early detection and containment of outbreaks is crucial for controlling the spread of avian flu.
Prompt reporting and action gives the best chance of limiting the impacts of infectious avian influenza.
Avian Flu Infection in Humans
Some avian influenza viruses also have the ability to infect humans, though this is relatively rare compared to human seasonal flu strains. People may become infected with bird flu viruses through direct contact with infected birds or contaminated environments. Symptoms are similar to other influenza infections, including:
- Fever and chills
- Cough and sore throat
- Fatigue and body aches
- Headache, runny nose and sneezing
- Nausea, vomiting and diarrhea (more common in avian flu)
While human infections with bird flu are usually mild, some strains like H5N1 and H7N9 can cause severe pneumonia and acute respiratory distress syndrome. These zoonotic avian influenza infections have a high fatality rate in humans, so prompt suspicion and treatment is essential.
People at increased risk of avian flu infection include poultry workers, laboratory personnel working with viruses, and healthcare providers of infected patients. Use of protective equipment and antiviral medications as a preventive measure should be considered for high-risk persons during outbreaks. Vaccine development efforts are also ongoing.
Key Facts About Avian Influenza in Humans
- Transmission to humans occurs through close contact with infected birds/environments.
- Symptoms resemble seasonal flu but diarrhea may also occur.
- Some strains like H5N1 have >50% mortality rate in humans.
- Prevention measures include PPE, antivirals, and potential vaccines.
While not a frequent cause of human infection so far, the potential exists for new avian influenza viruses to evolve increased transmissibility between humans, as was seen with past pandemics. Therefore, controlling flu viruses at their animal source remains a public and animal health priority.
Conclusion
Understanding the range of birds that can harbor and transmit avian influenza provides crucial insight into outbreak risks and prevention. Migratory waterfowl and shorebirds are natural reservoirs perpetuating diverse influenza viruses, including strains with pandemic potential. Domestic poultry are extremely susceptible to highly pathogenic forms which can decimate commercial flocks. Backyard and pet birds are also at risk, and certain wild bird populations appear to contract illness during outbreaks. Ongoing surveillance of avian species provides an important early warning system for veterinary and public health authorities. Robust prevention and containment measures are needed, especially in poultry, to stop avian flu viruses from spreading between flocks and potential transmission to humans. With collaborative monitoring and biosecurity efforts across public and animal health sectors, the threat of widespread influenza outbreaks arising from birds can be minimized.