What to know
- Bird flu is caused by infection with avian influenza A viruses that usually spread between birds, not people.
- People rarely get bird flu, but when they do, it is most often after close, unprotected exposure (without wearing respiratory or eye protection) to birds or other animals infected with avian influenza A viruses.
- No person-to-person spread of bird flu has been identified in the United States at this time. Very rare, limited person to person spread has occurred in other countries.
Causes
Bird flu is a disease caused by avian influenza A viruses that usually spread between birds. Avian influenza A viruses have caused sporadic human infections in multiple countries, including the United States. Most human infections have happened after exposure to infected animals.
Avian influenza A viruses that have infected humans
Five subtypes of avian influenza A viruses are known to have infected people. These are called A/H5, A/H6, A/H7, A/H9, and A/H10 viruses. Among these, A/H5, A/H7 and A/H9 viruses have caused the most human infections.
Current Health Risk to the Public is LOW
The risk to the general public from bird flu is currently low. Most cases of H5 bird flu in the United States have occurred among people with job-related or recreational exposures to birds, dairy cows, or other avian influenza A virus-infected animals or to contaminated products (e.g., raw milk) from infected animals. Some people have been infected with bird flu viruses from contact with their backyard poultry that were sick and died. Direct or close exposure to any animal with bird flu is a potential risk for human infection. Learn more: People at Increased Risk for Bird Flu
Birds that regularly become infected
Avian influenza A viruses infect birds' respiratory and gastrointestinal tracts and have been identified in more than 100 species of wild birds worldwide. Wild aquatic (water) birds, like gulls, terns, and shorebirds, and wild waterfowl, such as ducks, geese, and swans, are natural hosts of avian influenza A viruses. Some wild birds can be infected and show no signs of illness.
Songbirds commonly found in backyards in the United States can get infected
Avian influenza A viruses have been found in several common backyard birds including sparrows, pigeons, and crows. Avian influenza A viruses have been detected in some common backyard birds in the United States, but most common songbirds, like cardinals or blue jays have not been reported to get infected. It is still important; however, to take precautions around any kind of wild birds, especially that are sick or died.
CDC has more information about how to protect yourself as a bird watcher: Bird Hobbyists and Bird Flu
More information for backyard poultry owners: Backyard Flock Owners and Bird Flu
How it spreads
Avian influenza A viruses are thought to spread in a few ways:
- Direct contact between infected birds and other animals
- From contact with virus-contaminated environments or animal by-products
- Avian influenza A virus through the air (droplets or dust)
Very rare, limited person to person spread has occurred in other countries.
Exposure to infected birds or other animals
Direct and close contact with infected birds or other animals, including visiting a live poultry market, are exposures that have led to people becoming infected with bird flu. People can become infected after exposure to respiratory droplets, saliva, mucous, or feces that contain virus from infected birds or other animals. Human infections can happen when a person touches the virus and then touches their eyes, nose, or mouth.
From contact with virus-contaminated environments or animal by-products
People can also become infected by touching surfaces contaminated with infected bird mucous, saliva or feces and then touching their eyes, mouth or nose, or if liquid contaminated with live virus (like raw milk from an infected cow) splashes into your eyes. Infection can also occur if a person touches their eyelids, nose, or mouth with a finger or hand or glove that is contaminated with raw milk or other byproduct containing live avian influenza A virus.
It is also possible that you could become infected if you eat or drink something contaminated with virus.
Avian Influenza A virus through the air (droplets or dust)
People can also become infected when virus is in the air (in droplets or possibly dust) and a person breathes it in. The closer you are to an infected animal or contaminated environment, the more likely you are to become infected. Small dust particles and debris containing avian influenza A viruses can be expelled into the air and a person could inhale them.
Person to person (very rare)
Very rarely, limited spread of an avian influenza A virus has occurred in other countries from a sick person to another person who was not wearing recommended protective equipment. This has occurred in other countries after prolonged close exposure, such as when one family member was providing care for another family member who was very sick from avian influenza A virus infection.