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Frequently Asked Questions (FAQs)

  1. What is avian influenza?
  2. What are the differences between low pathogenic and highly pathogenic avian influenza viruses?
  3. How are influenza viruses classified?
  4. Why is highly pathogenic avian influenza (HPAI H5N1) causing such alarm?
  5. Has highly pathogenic H5N1 been found in North America?
  6. What kinds of wild birds primarily carry avian influenza?
  7. Can humans catch avian influenza from wild birds?
  8. Should hunters be concerned about avian influenza?
  9. Are migratory birds carrying the virus from one country to another?
  10. What are the potential vectors for a pathogenic strain of avian (or human) influenza to arrive in North America?
  11. Where are the most likely routes that H5N1 could enter the United States through migratory birds?

Colorized transmission electron micrograph of Avian influenza A H5N1 viruses
Colorized transmission electron micrograph of Avian influenza A H5N1 viruses (in gold).

1. What is avian influenza?

Bird flu, the popular name for avian influenza (AI), is a disease primarily found in poultry and wild birds. Avian influenza can infect chickens, pheasants, quail, ducks, geese, and guinea fowl, as well as migratory waterfowl and shorebirds and, less commonly, mammals (pigs, horses, cats, and marine mammals).

The virus is spread between birds through contact with fecal droppings, saliva, and nasal discharges of infected animals.

2. What are the differences between low pathogenic and highly pathogenic avian influenza viruses?

The designation of low or highly pathogenic avian influenza refers to the potential for these viruses to kill domestic poultry. The designation of "low pathogenic" or "highly pathogenic" does not refer to how infectious the viruses may be to humans.

Most strains of avian influenza are not highly pathogenic and cause few signs in infected wild birds; however, in poultry, low pathogenic strains can mutate into a highly pathogenic avian influenza (HPAI) strain that causes extremely contagious, severe illness, and often death, in poultry.

3. How are influenza viruses classified?

Influenza viruses are differentiated by two proteins, hemagglutinin (H) and neuraminidase (N), which are found on the surface of the virus. There are 144 theoretical combinations of the 16 different H and 9 different N proteins that make up the subtypes of avian influenza.

These subtypes can be further genetically differentiated into strains. A subtype such as the highly pathogenic H5N1 avian influenza virus may have multiple strains. These different strains may be more or less pathogenic to domestic poultry, wild birds, humans and other mammals.

Highly pathogenic avian influenza viruses in poultry are usually H5 or H7 subtypes of Type A influenza, although low pathogenic forms of these H5 and H7 viruses also exist.

Human influenza strains are usually H1 and H3 subtypes of Type A.

4. Why is highly pathogenic avian influenza (HPAI H5N1) causing such alarm?

This particularly virulent new strain of highly pathogenic avian influenza (HPAI H5N1) has spread throughout a large geographic area in Asia, Europe, and Africa since it was first documented in 1997 in Asia, and has caused the largest and most severe outbreaks in poultry on record.

Unlike most avian influenza viruses, this new strain of H5N1 has caused mortality in over 80 species of wild birds.

The human cases to date have been the result of direct or close contact with domestic (not wild) birds, especially chickens.

There are no documented cases of human H5N1 disease resulting from contact with wild birds.

So far, there has been no sustained person-to-person transmission of the HPAI H5N1 virus.

Public health organizations, such as the World Health Organization and the Centers for Disease Control and Prevention, are concerned that the virus could mutate into a human virus that would be more easily transmissible from person-to-person. This change could pose a global influenza pandemic threat.

5. Has highly pathogenic H5N1 been found in North America?

Researchers have no evidence that the Asian strains of HPAI H5N1 are present in wild birds or poultry in the North American continent.

Low pathogenic forms of H5 and H7 have occurred in both domestic and wild birds in North America.

6. What kinds of wild birds primarily carry avian influenza?

Long-tailed DuckMost avian influenza viruses have been isolated from wild waterfowl (ducks, geese, and swans) and shorebirds (wading birds), gulls, and terns.

With rare exceptions, the thousands of flu isolates found in wild birds have been low pathogenic avian influenza and have rarely caused signs of illness.

The occurrence of avian influenza in wild ducks in North America reaches its height in late summer and early fall. At other times of the year, infection rates are usually less than 1 percent.

In shorebirds, infection rates are highest during the spring migration, although in comparison with waterfowl, their infection rates are much lower.

7. Can humans catch avian influenza from wild birds?

There are no documented cases of wild birds directly transmitting avian influenza, including HPAI H5N1 to people.

The only documented cases of transmission to humans are from poultry; these cases include both highly pathogenic and low pathogenic strains of avian influenza.

At the present time, close contact with infected domestic poultry has been the primary way that people have become infected with the HPAI H5N1 virus.

8. Should hunters be concerned about avian influenza?

There is currently no indication that waterfowl or other wild birds hunted in the United States carry HPAI H5N1.

While experts believe the risk to hunters is currently low, scientists cannot guarantee that there is no risk. It is always wise to practice good hygiene when handling or cleaning any wild game.

9. Are migratory birds carrying the virus from one country to another?

The role of migratory birds in the transfer of the Asian H5N1 strain is not clear.

H5N1 has been identified in an increasing number of wild birds. The pattern and timing of several outbreaks have not coincided with periods of major migratory movements or migratory routes. However, there are also reports of wild bird mortality that are associated with outbreaks of HPAI H5N1 in poultry. It is not known if wild birds were the source of the virus or acquired the virus from poultry; although, once infected they could be a potential source of infection for domestic poultry that are not isolated from wild birds.

10. What are the potential vectors for a pathogenic strain of avian (or human) influenza to arrive in North America?

Bird migration is only one possible route of introduction of HPAI H5N1 into North America.

Illegal smuggling of birds and poultry products, travel by infected people or people traveling with virus-contaminated articles are more direct, and possibly more likely, means of introducing the new strain of HPAI H5N1 virus into the United States.

11. Where are the most likely routes that H5N1 could enter the United States through migratory birds?

Aleutian TernMigratory birds usually travel the same routes in their annual migrations. In the Northern Hemisphere, birds begin moving south during August and September of each year. North American migratory birds that over-winter in Asia may come into contact with potentially infected domestic or wild birds during the winter months.

In spring, migratory birds will migrate north to their breeding grounds in eastern Russia, Alaska, and Canada. Several species of migratory birds are known to share this intercontinental breeding region and migrate annually between North America and Asia. Migratory birds infected with the HPAI H5N1 returning from Asia could interact with other North American wild birds as they co-mingle on the breeding grounds.

There is also concern that migratory bird species, namely waterfowl, gulls, terns and shorebirds migrating between eastern North America and Northern Europe, could move viruses between continents.

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