Wild bird surveillance key to early H5N1 avian flu detection

Tragedy struck in early January when the first North American victim of the deadly H5N1 avian influenza died in an Edmonton hospital.

The individual travelled to Beijing in December and had recently returned home to Alberta. Investigations are ongoing into how the person contracted the virus and may shed light on how to minimize the risks to future travellers.

The emergence of H5N1 avian flu in Asia is a major public health concern. Since 1997, 648 human cases have been reported and of these, 384 were fatal. The lethality of this virus in people is what sets it apart from typical flu viruses.

Cases have been reported in 15 countries, with the majority occurring in China, Vietnam, Cambodia, Indonesia and Egypt.

Most human cases have been attributed to contact with infected domestic poultry, usually in live markets, and tend to occur in young adults and children.

H5N1 does not readily transfer between people, unlike seasonal flu, which is highly contagious. Perhaps the greatest risk to people will occur if the virus gains the ability to be transmitted between people.

H5N1 is considered to be a highly pathogenic influenza virus, meaning it causes high mortality in domestic birds.

Therefore, in addition to the risk to people, outbreaks of this virus have resulted in affected countries killing hundreds of millions of domestic birds. This response has failed to limit the spread, and the associated economic and social impacts have been astronomical.

Ducks and other wild waterfowl are the natural hosts of avian influenza viruses, where they circulate in low-pathogenic forms. These birds carry and shed the virus without causing disease, but it can mutate and cause high rates of mortality if it gets into domestic poultry.

The transportation of infected people and domestic birds around the world is likely how H5N1 will be introduced, although wild birds are another possible route into North America.

It’s why the Canadian Co-operative Wildlife Health Centre co-ordinates the Canada Interagency Wild Bird Survey, which tests birds for all avian influenza viruses. The survey gathers information on which strains of influenza are circulating in wild bird populations.

More than 1,000 birds were tested last year, and two were positive for the run-of-the-mill North American strain of avian influenza. The survey has tested 8,800 birds over the past five years, and none were infected with the H5N1 strain.

“Vigilance is needed because if a highly pathogenic virus were to arrive in North America by any means, it could cause disease or mortality in poultry, people or wildlife. Early detection requires surveillance in all three groups,” said Dr. Ted Leighton, the centre’s national director.

The survey began following the outbreak of high pathogenic avian influenza (H7N3) in British Columbia’s Fraser Valley in 2004. It was eradicated after 17 million birds were culled and more than $300 million in economic losses were incurred.

Other strains of avian influenza continue to crop up in Asia and represent an ongoing threat to public and animal health.

“These viruses are highly flexible and they change rapidly. There is constant movement between wild bird populations and domestic birds,” said Leighton.

Biosecurity remains essential to prevent future outbreaks of highly pathogenic avian influenza and potential establishment of H5N1 in North America.

The human risk of contracting H5N1 remains low, but the tragic loss of a Canadian to this virus serves as a reminder that diseases elsewhere in the world are only a plane ride away.

Dr. Jamie Rothenburger is a veterinary pathology resident at the Western College of Veterinary Medicine, University of Saskatchewan.

Respond





You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>