Monday, December 12, 2016

Japan: Wild Bird Surveillance & Detection Of H5N6


Excluding poultry, Japan - as of 1700 hrs (local time) December 12th has now recorded 53 separate detections (of one or more) HPAI positive wild birds across 11 Prefectures.

Not all of these reports have been validated as due to H5N6, but those that have been fully tested have all turned out to be of this subtype. 

Japan's Ministry of Environment handles the non-farm detections of the virus (wild birds & environment), and their Information about the highly pathogenic avian influenza web page has been updated almost daily since H5N6 arrived in Japan in mid-November.

Since we last checked in on Wednesday (see Japan : Wild Bird H5N6 Update, the MOE has posted 22 new reports (see below). 

While the detection of HPAI viruses in wild and migratory birds is nothing new, in the past they've been more sporadic and less pathogenic than what we've witnessed over the past couple of months with H5N6 in Asia and H5N8 in Europe. 

It was only just over four months ago, in PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl, that researchers looked for - and failed to find - HPAI in North American wild birds in the year following our (HP) H5N1, H5N2, and H5N8 epizootic over the winter of 2014-15. 

The authors concluded:  
While wild ducks and other aquatic birds are known to be natural hosts for low pathogenic flu viruses associated with milder symptoms, the results of this study indicate that is not the case with the highly pathogenic flu viruses that are associated with more severe illness. The research suggests that wild ducks and other aquatic birds are not an ongoing source of highly pathogenic flu infection in domestic poultry.  
Although time may again prove that to be true with these latest subtypes, and they may recede next summer as they did after the North American epizootic of 2014-15, it is hard not to come away with the notion that something has changed with these new HP H5Nx clade viruses. 

One possibility, proffered by a study published last month (see EID Journal: HPAI A(H5Nx) Viruses With Altered H5 Receptor-Binding Specificity), suggested that recent amino acid changes enable clade H5 viruses to now bind to fucosylated sialosides.
Receptor cells that differ from the sialic acid (a2,3 avian or a2,6 mammalian) that influenza viruses normally bind to.

While the full impact of this change in receptor binding remains unknown, the authors suggest `Altered receptor-binding properties might affect the balance between HA and NA, enable the virus to acquire different NA subtypes, and might result in altered host range and spreading.' 

Or it could be something else entirely. 

At this point, the only thing certain is that HPAI H5 appears to be well into its 4th Intercontinental Wave since it reemerged in 2003, and it doesn't show any signs (yet) of slowing down.

No comments: