Source: Posted by Ian M Mackay on Virology Down under. CDC Emerging Infectious Diseases published a paper (Volume 19, Number 12—December 2013) on the Historical Prevalence and Distribution of Avian Influenza Virus A(H7N9) among Wild Birds. A very interesting document, it provides a better understanding on transmission of H7N9 under wild birds.

In this paper, the authors reviewed 48 published studies that listed findings of influenza A virus haemagglutin type H7, or neuramonase N9 viruses as well as H9N2. The prevalence was calculated as the number of positive samples divided by the by number tested.

H7N9 has been rarely reported from Delaware (USA), Alberta (Canada), Guatemala, Spain, Egypt, Mongolia and Taiwan but has not been reported from Russia, Japan, South Korea or China from birds sampled between 1976-2012.

The outcome? If you were planning wild bird surveillance to track H7N9 spread in these non-poultry animals, you’ll need to sample >30,000 wild birds to find 1 positive for H7N9 (its Asian prevalence was 0.00931%).

That’s a rare bird.
This is just a rough gauge of course because it is entirely dependent on when, where and how thoroughly bird populations were sampled, how they were sampled, what they were tested with and how the sequencing methods performed. It also focuses on HA and NA genes, at the expense of other internal influenza gene segments which also have an important role in the assemblage of new viruses.

Related links to this topic published by FAO-USGS on Avian Influenza Projects related to migrating birds:

Avian Influenza transmission risk & the Migratory Ecology of African wild ducks
Avian Influenza transmission risk & wild birds in Nigeria
Bangladesh: A source of Highly Pathogenic H5N1 infection in wild birds?
Ecology and Conservation of Wild Birds in the Poyang Lake Region: a Satellite Telemetry Pilot Project
Investigating the role of swans and geese from Eastern Mongolia in the potential spread of avian influenza virus.
Migratory birds and transmission of Highly Pathogenic H5N1 in Turkey
Movements of migratory waterfowl in the Middle East: Identifying at-risk areas for spread of avian influenza into Egypt
Movements of Wild Birds and Emerging Disease Risk from Hong Kong
Movements of Wild Birds and Emerging Disease Risk from India
Wild Bird Migratory Ecology, Emerging Disease Risk and Physiology in Western Mongolia
Wild Birds and Emerging Diseases: Avian Influenza Transmission Risk and Movements of Wild Birds from Kazakhstan
Wild Birds and Emerging Diseases: Modeling Avian Influenza Transmission Risk Between Domestic and Wild Birds in China


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