Bird flu, also known as avian influenza, is a viral infection that can affect various species of birds. There are many different strains of avian influenza viruses that can vary in their ability to cause disease and transmit between birds and other animals. The most well-known bird flu virus, H5N1, has caused large outbreaks in domestic poultry and some concerns about its potential to transmit to humans. However, H5N1 is known to mostly affect domestic and wild waterfowl and shorebirds, rather than songbirds.
What is bird flu?
Bird flu refers to illness caused by infection with avian (bird) influenza A viruses. These viruses naturally occur in wild birds worldwide, especially in waterfowl and shorebirds. Avian influenza viruses are classified by a combination of two groups of proteins on their surface: hemagglutinin or “H” proteins, of which there are 16 (H1 to H16), and neuraminidase or “N” proteins, of which there are 9 (N1 to N9).
Some strains, like the highly pathogenic H5N1, can produce severe disease and death in domestic poultry, wild birds, and occasionally in humans, but most bird flu strains cause little to no symptoms in birds. Avian influenza viruses are very species-specific, meaning certain strains only infect certain species, and do not easily jump between taxonomic groups.
Do songbirds get bird flu?
Songbirds are generally not considered a natural reservoir for avian influenza viruses like waterfowl and shorebirds. Most surveillance studies have shown that songbirds have a very low prevalence of avian influenza infection compared to waterbirds. There are a few reasons why songbirds are less affected:
- Songbirds and waterbirds have differences in their respiratory and digestive physiology that make waterbirds more susceptible to infection.
- Songbirds migrate at night over land, while waterbirds migrate during the day over water routes that facilitate virus transmission.
- Waterbirds congregate in large flocks at wetlands where they can exchange viruses, unlike songbirds.
However, there is some evidence of certain avian influenza strains infecting and causing death in songbirds, especially highly pathogenic strains like H5N1. During large outbreaks, the virus has spilled over from waterbirds to songbirds, likely through direct contact around habitats or fecal-oral transmission. But this represents spillover infection, not sustained circulation within songbird populations.
Documented cases of bird flu in songbirds
Here are some examples of bird flu outbreaks that affected songbirds:
- In 1961, over 1,000 common terns died in South Africa due to H5N3 flu.
- In 2005, H5N1 caused the death of over 6,000 migratory birds, including tree sparrows, in Qinghai Lake, China.
- In 2006, a captive mountain canary died of H5N1 infection in the United Kingdom.
- In 2010-2011, a H5N1 outbreak in Japan caused the death of several hundred bull-headed shrikes.
However, these represent just a handful of isolated cases over decades of surveillance in songbirds. The likelihood of a given songbird being infected with or dying from bird flu remains extremely low compared to waterbirds. Nonetheless, evidence shows highly pathogenic strains can spill over into songbird populations during large outbreaks in local waterfowl when there is environmental contamination.
Symptoms of bird flu in songbirds
When songbirds are infected with virulent bird flu strains, either through experiment or natural exposure, they may develop the following symptoms:
- Loss of appetite
- Difficulty breathing
- Diarrhea
- Discharge from eyes and nose
- Swollen head
- Cyanosis (blue discoloration) of skin and legs
- Tremors and seizures
- Sudden death
However, many songbird infections may be mild or asymptomatic, allowing birds to recover. Mortality rates in songbirds are typically lower than poultry. Sudden die-offs of multiple songbirds in an area may indicate a localized bird flu outbreak.
Risks to humans
Bird flu is primarily an animal disease, though some strains like H5N1 and H7N9 have caused human infections and deaths. The main risk factors are close, prolonged contact with infected poultry. There has been no evidence of human transmission from infected songbirds.
Precautions for humans around sick or dead songbirds include:
- Avoid touching feathers, surfaces near roosting areas
- Wear gloves and wash hands if handling
- Cook poultry thoroughly to temperatures >165°F (74°C)
For bird flu to be transmissible between humans, the virus would need to acquire genetic changes through some unlikely recombination event. Routine surveillance continues to monitor bird flu viruses for any concerning mutations.
Prevention in birds
Biosecurity measures used to control bird flu in poultry flocks can also help protect wild birds by limiting environmental spread:
- Keep wild and domestic birds separate
- Disinfect equipment and cages
- Report sick birds
- Restrict access to infected areas
Vaccination of poultry against H5 and H7 viruses can also help reduce shedding and transmission to wild birds. Proper carcass disposal and disinfection helps remove sources of virus contamination.
Conclusion
In summary, avian influenza viruses are primarily adapted to waterbirds like ducks and geese. Songbirds are sporadically affected during major outbreaks through contact with infected waterfowl or virus in the environment. Certain highly pathogenic strains like H5N1 can overcome species barriers and cause illness and death in songbirds. However, this represents spillover infection, not routine transmission cycles within songbird populations. Proper biosecurity and monitoring can help detect and contain outbreaks to protect both poultry and wild birds.
