Avian Influenza and Migratory Birds
Background
What is avian influenza?
Avian influenza (AI) is a contagious viral infection caused by the influenza virus Type "A", which can affect several species of food producing birds (chickens, turkeys, quails, guinea fowl, etc.), as well as pet birds and wild birds. Type A influenza viruses are present in a wide variety of birds and mammals and new strains are constantly evolving. World wide, most avian influenza strains originate in wild waterfowl, where they seldom cause illness. Some avian influenza viruses cause problems when they become established in domestic poultry, where they may cause either mild (low pathogenicity strains) or severe (high pathogenicity strains) disease. For example, in 2004, there was an outbreak of highly pathogenic avian influenza (H7N3) in poultry in the Fraser Valley of British Columbia. This strain was thought to have developed when a strain of low pathogenicity from wild waterfowl entered a domestic flock and evolved into a highly pathogenic strain.
What is H5N1 avian influenza?
H5N1 is a particular subtype of the avian influenza virus. Within this subtype of the virus, there are different genetic strains with different biological properties. Some strains cause mild disease in poultry (known as low pathogenicity strains) while others cause severe, even fatal, disease in poultry (defined as high pathogenicity).
Low pathogenicity H5N1 strains are genetically and biologically different from the high pathogenicity strains of H5N1, such as those currently circulating in Eurasia. Low pathogenicity H5N1 strains have previously been found in wild birds outside of North America without causing disease or die-offs. Recently, low pathogenicity H5N1 strains were found in a few samples from healthy wild birds in Canada. These strains are thought to be native to North America, and are not closely genetically related to the highly pathogenic "Asian strain" of H5N1.
Are avian influenza, human influenza, and pandemic influenza the same?
Avian influenza viruses originate in birds and generally cause problems only in domestic poultry. On rare occasions, the viruses may mutate or exchange genetic material with other influenza viruses, which results in a strain that can be transmitted from poultry to people (zoonosis).
Human influenza, or the flu, is a respiratory infection caused by the influenza virus. Strains circulate every year, making people sick. Influenza typically starts with a headache, chills and cough, followed rapidly by fever, loss of appetite, muscle aches and fatigue, running nose, sneezing, watery eyes and throat irritation. Nausea, vomiting and diarrhoea may also occur, especially in children.
Three to four times each century though, for unknown reasons, a radical change takes place in the influenza A virus causing a new strain to emerge to which people have little or no immunity. Sometimes this happens because an influenza virus mutates in humans, or human and avian influenza viruses mix to create a new strain. If this new strain is easily passed between people, this creates the conditions for an influenza epidemic, which can lead to a pandemic if the strain spreads globally.
Asian strain H5N1 is considered a potentially zoonotic avian influenza virus that has caused limited human illness in Asia since 2003.
See the relevant public health websites for more information about avian influenza as a zoonosis, and about human influenza.
What is the role of migratory birds in the H5N1 outbreak in Eurasia?
The pattern of outbreaks of Asian strain H5N1 avian influenza in Eurasia suggests that migratory birds may have contributed to the spread of this virus. It has also raised concerns that migratory birds may bring Asian strain H5N1 avian influenza to North America, where it is not thought to be present. There are native North American strains of H5 influenza, or possibly even H5N1, circulating in wild birds that may have no health significance for wild or domestic birds.
The role played by migratory birds in transmitting avian influenza is unclear and the source of much speculation. The strains detected in Canadian wild birds have not caused detectable disease in wild birds to date. Even in Eurasia, relatively few populations and species of wild birds have been affected by Asian strain H5N1.
Environment Canada is cooperating with other federal agencies and with provincial and territorial agencies in avian influenza surveillance studies and will be part of a coordinated response team should we detect highly pathogenic strains in wild birds.
More information on avian influenza is provided in the Frequently Asked Questions (hotlink) and at the links provided below.
Environment Canada's response to avian influenza
Environment Canada is a leading contributor to the National Wildlife Disease Strategy. The strategy provides a national framework to address wildlife disease issues and aims to minimize the damaging effects of wildlife diseases on wildlife, livestock, human health and the economy.
The Canadian Wildlife Service is actively participating in the monitoring and reporting of avian influenza in Canada among migratory birds. While migratory birds are natural reservoirs for avian influenza, most strains pose little risk to humans or poultry as long as barriers between wild and domestic birds are maintained; the Canadian Food Inspection Agency provides recommended practices. Better understanding of the occurrence of different strains of Avian Influenza in wild birds in Canada is the basis for an on-going study by the Canadian Cooperative Wildlife Health Centre with the Canadian Wildlife Service, the Canadian Food Inspection Agency, the Public Health Agency of Canada and several provinces.
The Food and Agriculture Organization, the World Organization for Animal Health and the World Health Organization have all stated that culling wild birds is not indicated or effective in preventing the spread of highly pathogenic avian influenza viruses, such as H5N1, to domestic poultry. Transmission of avian influenza from wild birds directly to humans has never been documented. Following biosafety precautions when handling wild birds will keep the risk of transmission low.
Coordination with Other Agencies
Avian influenza directly affects domestic poultry producers and has implications for public health. Environment Canada is therefore working very closely with the Canadian Food Inspection Agency, the Public Health Agency of Canada, the provinces/territories, and the Canadian Cooperative Wildlife Health Centre to monitor avian influenza in Canada, and to ensure a well integrated and coordinated response to the evolving situation.
The Canadian Cooperative Wildlife Health Centre undertakes national wildlife disease surveillance, provides scientific information to partner agencies and responds to major wildlife disease issues. The Centre is managed by a board of directors, which includes the Canadian Wildlife Directors Committee, of which the Director General of the Canadian Wildlife Service is a member. The Canadian Food Inspection Agency and the Public Health Agency of Canada are also members. The Canadian Wildlife Service continues to participate in on-going research on avian influenza coordinated by the Canadian Cooperative Wildlife Health Centre.
The Canadian Wildlife Service is in regular contact with our American counterparts at the U.S. Fish and Wildlife Service to share information and develop compatible approaches for surveillance and management of avian influenza in migratory birds. Both agencies are contributing to an enhanced scientific understanding of avian influenza in wild birds and are providing advice to their client groups.
At the moment there is no new risk to human health. However, recent investigations and media coverage of avian influenza in wild birds have increased awareness of and concern about the safety of handling and hunting wild birds. Migratory game bird hunting permit holders, aviculture permit holders, holders of scientific permits to capture and band migratory birds, and others who are in close contact with wild birds should always take precautions to minimize their risk of exposure to avian influenza and other diseases. Recommended Biosafety Practices are provided below.
