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Avian Influenza: History

Avian Influenza Worldwide | Avian Influenza in Canada

Avian Influenza Worldwide*

Domestic Birds

Avian influenza (AI) viruses are not new. The first outbreak of highly pathogenic AI in domestic birds was reported over 100 years ago in Italy. Since then, subsequent cases of the disease have cropped up in domestic flocks in several countries around the world.

There are many known influenza subtypes, however, only H5 and H7 subtypes are known to become highly pathogenic in avian species. Pathogenicity refers to the severity of the illness caused in poultry.

The highly pathogenic Asian strain of H5N1 AI, which is the current focus of international animal health and human health authorities, was first detected from a goose farm in China in 1996. The virus has since resurfaced and been detected in parts of Asia, Africa and Europe. It has been known to infect multiple species of domestic (chickens, turkeys, quails, guinea fowl, etc.), wild and pet birds, resulting in high mortality rates. This virus has also been isolated from mammalian species including humans, rats and mice, weasels and ferrets, pigs, cats and dogs.

Recent outbreaks of highly pathogenic H5N1 AI in domestic birds occurred in Hong Kong (1997-1998 and 2003), the Netherlands (2003) and the Republic of Korea (2003).

Outbreaks of highly pathogenic AI, regardless of the strain, are not easy to control. Infected birds must be destroyed, and stringent movement and biosecurity controls must be imposed in order to prevent spread of the disease.

Wild Birds

Wild birds have historically been known as reservoirs for AI viruses, mostly of low pathogenicity. In 2002, mortalities in wild birds due to highly pathogenic avian influenza (HPAI) were reported in Hong Kong. These were the first reported deaths of wild birds as a result of HPAI in Asia, according to the Food and Agriculture Organization of the United Nations (FAO).

Animal health organizations around the world, including the Canadian Food Inspection Agency (CFIA) have surveillance measures in place to monitor patterns of AI viruses in wild birds.

*Source: Food and Agriculture Organization of the United Nations (http://www.fao.org)

Avian Influenza in Canada

In the 1960s, when turkeys were often raised outdoors, cases of low pathogenicity AI were often reported in the autumn. Since the sixties, the majority of domestic poultry have been raised in closed poultry houses to control other diseases and are managed under more stringent biosecurity conditions. As a result, subsequent detection of H5 or H7 subtypes of AI has been rare. The latest were reported in 2004 and 2005.

In February 2004, the CFIA identified the presence of low pathogenicity H7 AI in birds from a commercial chicken breeder farm in British Columbia’s Fraser Valley. Subsequent tests revealed that the virus had changed to highly pathogenic H7 AI. Other farms in the area were quickly identified as having HPAI, as well. The CFIA depopulated all infected premises (42 commercial and 11 backyard premises) on which highly pathogenic AI was found and pre-emptively destroyed birds in the surrounding three-kilometre areas.

In November 2005, the CFIA announced that the AI virus detected in a duck from a farm in British Columbia was confirmed as a low pathogenicity H5 North American strain. Testing was conducted on a priority basis at the National Centre for Foreign Animal Disease (NCFAD) in Winnipeg. The infected flocks were depopulated and surveillance was conducted to monitor bird health by sampling all neighbouring commercial poultry operations within five kilometres.

The CFIA, in partnership with other government and non-government organizations, continues to monitor commercial and non-commercial flocks and wild birds in Canada for AI viruses.

For information on wild bird surveillance in Canada, please see the Wild Bird Survey (2006).

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