Notes from the Science Committee: Frequently Asked Questions
Most of us have heard or read about avian influenza (also called avian flu and bird flu) and its impacts on domestic poultry. We have reviewed many sources of information, some of which are listed below. Following are some answers to the most commonly asked questions:
Is Avian Flu a New Type of Flu?
No, avian influenza was first identified more than 100 years ago during an outbreak in Italy. Since then, the disease has cropped up at irregular intervals in all regions of the world. In the U.S., the Centers for Disease Control and Prevention (CDC) maintains updated information on the latest situation.
Current H5N1 bird flu viruses were first identified in Europe during the fall of 2020 and spread across Europe and into Africa, the Middle East and Asia, becoming the predominant subtype globally by fall of 2021.
Avian influenza viruses infect chickens, turkeys, pheasants, quail, ducks, geese, and guinea fowl, as well as a wide variety of wild birds, including shorebirds, raptors, and gulls. Migratory waterfowl – most notably wild ducks – are the natural reservoir hosts of avian influenza viruses, and these birds are also the most resistant to infection.
The avian influenza viruses belong to the type A influenza virus, of which there are many different subtypes. These subtypes differ because of certain proteins on the surface of the virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 different HA subtypes and 9 different NA subtypes. Many different combinations of HA and NA proteins are possible. Each combination is a different subtype. All subtypes of influenza type A viruses can be found in birds. However, when we talk about “bird flu” viruses, we are referring to those subtypes that continue to occur mainly in birds. They do not usually infect humans, even though they can and sometimes do. When we talk about “human flu viruses” we are referring to those subtypes that occur widely in humans. There are only three known subtypes of human influenza viruses (H1N1, H2N2, and H3N1).
Get more detailed information on avian influenza viruses and how they change over time.
Is Avian Flu Normally Fatal to Birds?
The many subtypes of avian influenza viruses that occur worldwide cause varying degrees of clinical illness in poultry. Chickens and turkeys are particularly susceptible to epidemics of rapidly fatal influenza.
Influenza viruses infecting poultry can be divided into two distinct groups on the basis of their ability to cause disease. The highly pathogenic avian influenza viruses (HPAI) cause high mortality in infected poultry, sometimes up to 100 %. All other virus subtypes cause a much milder, primarily respiratory, disease. Only those viruses that cause mild disease in poultry have been isolated from wild birds and, under natural conditions, are not known to cause disease in these species.
How is Avian Influenza Spread?
Can Birds Be Infected at Bird Feeders?
Theoretically yes, because of the fecal route of excretion of the virus and its ability to stay viable and infectious at low temperatures – usually the very time of year when we are most diligent about feeding our backyard birds. However, with passerines being the most common visitors to bird feeders, and the frequency of infection in these species being very low indeed, the risk may safely be considered remote.
Of much more concern are other easily transmitted infections such as salmonellosis (a bacterial infection), avian pox, and various fungal infections. It is important, therefore, to clean feeders frequently and disinfect them with bleach or vinegar at least once a month.
Are Possibly-Infected Wild Birds a Danger to Humans?
Can Avian Flu be Transmitted from One Person to Another?
Should I Be Cautious if I Encounter a Dead Bird?
Yes, but not necessarily because of avian flu. The vast majority of birds that are found dead have died of causes other than diseases communicable to humans. If you need to move a dead bird, use precautions such as wearing gloves or using a long-handled shovel or other tool to move the bird. If you need to handle the bird, bag it tightly. In light of the West Nile virus endemicity in the US, we recommend that you contact your local public health department if you find a dead bird, especially crows, jays, or raptors. In Seattle and King County contact the Environmental Health Services Division.
Where Can I Get More Information About Avian Flu?
- Washington Department of Fish & Wildlife
- Department of Health and Human Services
Avian Influenza Q & A, UN Food and Agricultural Organization
- Birdlife International
- Veterinary Medicine, UC Davis
- World Health Organization
- US Department of Agriculture
For information specifically relevant to the influenza situation in the USA, refer to the CDC website and links listed there. From October through May, surveillance information is updated each week, and can be found on the Flu Activity Page of the CDC website. The site also includes international surveillance data of relevance to those intending to travel. In addition, periodic updates regarding influenza are published in the MMWR Weekly.