What Is Bird Flu?
Bird flu, or avian influenza, is a viral infection spread from bird to bird. The most common kind of bird flu is the H5N1 strain. It's mostly a threat to birds and doesn’t spread easily among people, but there was a major outbreak of bird flu in people in 2014. The very few cases of human-to-human transmission were among people with exceptionally close contact, such as a mother who caught the virus while caring for their sick infant.
Migrating water fowl -- most notably wild ducks -- are the natural carriers of bird flu viruses. Scientists suspect that infection can spread from wild fowl to domestic poultry.
What Are the Symptoms of Bird Flu?
Bird flu symptoms in people can vary. The illness could start out with flu-like symptoms that include fever, cough, sore throat, and muscle aches. But it may worsen to include:
- Gut problems: Nausea, belly pain, diarrhea, and vomiting.
- Breathing problems: Shortness of breath, serious respiratory distress or failure, pneumonia, and other respiratory diseases.
- Brain or nervous system changes: You might notice shifts in behavior, thinking, or even organ function. Seizures are possible in serious cases.
In February 2005, researchers in Vietnam reported human cases of bird flu in which the virus infected the brains and digestive tracts of two children. Both died. These cases show that bird flu in humans may not always look like typical cases of flu.
Scientists have identified more than a dozen different strains, or variants, of bird flu. H5N1, one of the deadliest strains for humans, has caused 456 bird flu deaths since 2003, according to the World Health Organization.
How Do Humans Get Bird Flu?
People catch bird flu by close contact with birds or bird droppings.
In the 2014 outbreak, some people caught H5N1 from cleaning or plucking infected birds. There were reports in China of infection via inhalation of aerosolized materials in live bird markets. It's also possible that some people were infected after swimming or bathing in water contaminated with the droppings of infected birds. And some infections have occurred in people who handle fighting cocks.
People don't catch the virus from eating fully cooked chicken or eggs.
There were a few cases where one infected person caught the bird flu virus from another person, but only after close personal contact.
In Indonesia in 2006, bird flu spread to eight members of one family. Seven of them died. It's not clear exactly how this happened. Family members likely had similar contacts with infected birds. They may also have shared genes that made them particularly susceptible to the virus. However, casual contact does not seem to be involved.
Has Bird Flu Been Seen in the U.S.?
Various strains of bird flu pop up in U.S. poultry from time to time. When they do, all affected poultry flocks are culled.
For example, in 2004, a highly dangerous bird flu strain appeared in a Texas chicken flock. The outbreak involved an H5N2 virus (not the H5N1 bird flu). By April 2004, the outbreak had been eradicated. No human infections were detected.
What Are the Types of Bird Flu?
The bird flu virus, avian influenza A, is divided into two main categories:
- Highly pathogenic avian influenza (HPAI) causes more serious illness in chickens and is more likely to kill them.
- Low pathogenicity avian influenza (LPAI) causes less serious illness in chickens and is less likely to cause death.
Both versions can spread quickly through bird flocks and may cause serious illness in humans. This is important because birds infected with LPAI viruses may show little or no sign of disease as it spreads to animals or humans.
Viruses often change over time, leading to different subtypes called strains. When bird flu infects humans, which is rare, it's most often from strains known as H5, H7, and H9. Less commonly, researchers have detected H10N8, H10N7, and H6N8 strains in humans.
Is There a Bird Flu Vaccine?
Yes, but you can't make an appointment to get it. The FDA approved the first vaccine to prevent human infection with one strain of the bird flu (H5N1) in 2007. But it’s not been made commercially available to the general public. The U.S. government purchased the vaccine in case it needed to be distributed by public health officials.