Birds & Science
Avian Influenza Information
(May 22, 2007) With widespread interest in avian influenza or “bird flu”, Audubon is providing the following information and links as a resource for those who may be concerned about avian influenza, as well as about how birds are involved. Also included are some general precautions for protecting both human and bird health.
Background on Avian Flu
There are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins (hemagglutinin [HA] and neuraminidase [NA]) on their surface. There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. In addition, each subtype can be further classified into strains based on different mutations found in each of its 8 genes. All known subtypes of influenza A viruses can be found in birds.
Avian influenza viruses circulate among birds worldwide. Certain birds, particularly water birds, act as hosts for influenza viruses by carrying the virus in their intestines and shedding it. Infected birds shed the virus in their saliva, nasal secretions, and feces. Susceptible birds can become infected with avian influenza virus when they have contact with contaminated nasal, respiratory, or fecal material from infected birds. Most often, the wild birds that are host to the virus do not get sick, but they can spread influenza to other birds. Some highly pathogenic (HP) strains of avian influenza are very dangerous to poultry and other domestic birds, while other low pathogenic (LP) strains are not considered dangerous.
Bird flu viruses do not usually infect humans, but confirmed cases of human infection from several subtypes of bird flu viruses have occurred since 1997. Most cases of avian influenza infection in humans have resulted from direct or close contact with infected poultry (e.g., domesticated chicken, ducks, and turkeys) or surfaces contaminated with secretions and excretions from infected birds. The spread of avian influenza viruses from an ill person to another person has been reported very rarely, and transmission has not been observed to continue beyond a small cluster of closely associated individuals. During an outbreak of avian influenza among poultry, there is a possible risk to people who have direct or close contact with infected birds or with surfaces that have been contaminated with secretions and excretions from infected birds.
H5N1: A Current Strain of Avian Influenza Virus
The H5N1 Highly Pathogenic Avian Influenza virus – also called “H5N1 virus” – is an influenza A virus subtype that occurs mainly in birds, is highly contagious among domestic birds, and can be deadly to them. HPAI H5N1 virus does not usually infect people, but more than 306 human cases (and 185 deaths) have been reported in Azerbaijan, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Lao People’s Democratic Republic, Nigeria, Thailand, Turkey, and Vietnam since January 2004. Most of these cases have occurred from direct or close contact with infected poultry or contaminated surfaces; however, a few cases of human-to-human spread of H5N1 virus have occurred. So far, the spread of H5N1 virus from person to person has been rare and has not continued beyond a small cluster of closely associated individuals. Nonetheless, because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day could be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population.
Since late June 2004, outbreaks of influenza H5N1 among poultry have been reported in at least 61 countries in Asia, Europe, and Africa. In January 2006 the virus was first reported in several European Union countries, and was also detected in several more European countries and several countries in Africa in February 2006. These outbreaks are ongoing, with new cases confirmed almost daily, and some authorities expect the virus to become endemic throughout Europe. Globally, over 200 million domestic birds have been culled to contain outbreaks.
Do Wild Birds Transmit H5N1 to People?
In the summer of 2005, the virus spread to Central Asia and China where it was detected in both domestic birds and wild birds. By October 2005, the virus was detected in domestic ducks and poultry in Turkey and Romania, and a wild Mute Swan in Croatia. In November it was detected in a flamingo in Kuwait. In February 2006, H5N1 was found in Mute Swans and a few other wild birds in several European countries. So far, there has only been one case where humans have presumably contracted H5N1 avian influenza directly from wild birds—villagers in Azerbaijan who illegally harvested feathers from dead infected swans. Relatively few cases were reported in Europe during the winter of 2006-2007. Spring 2007 outbreaks in western Africa are thought to be caused by illegal poultry smuggling.
Researchers are still trying to determine how well wild birds may be able to carry and transmit the H5N1 virus. In 2006, testing in European Union countries found H5N1 avian influenza in 741 of over 60,000 wild birds tested. However, during that same period there were only four poultry outbreaks, and no human cases reported in the European Union. While wild birds may conceivably carry and even transmit H5N1 avian influenza virus to humans, there is no evidence that wild birds can transmit the virus to humans without close or prolonged contact with infected birds. Wild birds are not thought to be the main carriers of this virus. The most recent evidence suggests that while wild birds may occasionally carry H5N1 short distances, H5N1 is most often spread through the shipment of poultry, poultry products, and poultry manures.
Leading experts including the World Health Organization, Food and Agricultural Organization of the United Nations, and World Organization for Animal Health all emphasize that culling wild bird populations is highly unlikely to stop the spread of the disease, and would only divert resources away from more important disease control measures. (See statements by UN Food and Agricultural Organization http://www.fao.org/newsroom/en/news/2004/48287/index.html).
Has H5N1 Been Found in North America?
The highly pathogenic form of H5N1 avian influenza virus has not been found in wild birds in North America. In 2005, a low pathogenic form of H5N1, which is not thought to pose a danger to poultry or humans, was found in wild ducks in Canada. In August 2006, two Mute Swans with a low pathogenic form of H5N1 were found in the Michigan. Additional cases of harmless LPAI H5N1 continue to be found in waterfowls across North America.
There is a remote chance that infected wild birds from Asia or Europe could bring the highly pathogenic form of the virus with them during spring or fall migration to North America. The US Fish and Wildlife Service, US Geological Survey (USGS), Alaska Department of Fish & Game, and public health agencies are working together to test thousands of waterfowl and shorebirds for the virus in Alaska, and field sampling is being integrated with surveillance programs throughout the United States and Canada. In 2006, 147,609 birds were tested in the United States without any being found to carry the dangerous H5N1 virus. So far in 2007, over 525 birds have been tested without any testing positive for HPAI H5N1.
What You Can Do
1) While the possibility of contracting the H5N1 virus from wild birds is very unlikely, people who have close personal contact with wild birds should take measures to protect themselves by practicing animal handling and sanitary practices recommended by the USGS National Wildlife Health Center Wildlife Health Bulletin #05-03 (http://www.nwhc.usgs.gov/publications/wildlife_health_bulletins/WHB_05_03.jsp).
2) People who feed birds are not at high risk of contracting avian influenza from birds in their yards or at their feeders. However, anyone who comes into direct content with birds and their droppings should follow the recommended USGS sanitary practices, and since birds can transmit other diseases to humans (e.g. salmonellosis), people who feed birds should routinely clean their feeders and bird baths as recommended by Audubon (http://www.audubon.org/bird/at_home/SafeFeeding.html) and the USGS National Wildlife Health Center (http://www.nwhc.usgs.gov/publications/fact_sheets/coping_with_diseases_at_birdfeeders.jsp).
Centers for Disease Control
GRAIN report on avian influenza and global poultry industry
United Nations Food and Agricultural Organization
National HPAI Early Detection Data System
ProMED-mail Program for Monitoring Emerging Diseases
USGS National Wildlife Health Center
United States Fish and Wildlife Service
BirdLife International Statement on Avian Influenza
Wetlands International Statement on Avian Influenza