The Continued Expansion of HPAI H5N5

Map Credit Wikipedia

#18,455

The HPAI H5 influenza virus continues to evolve, and over nearly 3 decades it has produced dozens of clades and subclades, hundreds of genotypes, spanning 9 different subtypes (H5N1-H5N9).  

While H5N1 is currently our biggest avian flu concern, in the past H5N8 and H5N6 have both threatened - and we've recently been watching the rise of HPAI H5N5 in both Europe and Canada.

New subtypes or new genotypes of the HPAI H5 virus are a product of H5 reassorting with other LPAI viruses - which can occur in both birds and mammals around the globe.  Most are unable to compete with their parental viruses and fade away, but occasionally one will emerge that is able to thrive.  

 

While we'd seen reports of H5N5 in European birds going back to 2016, it was detected in dead raccoons on Prince Edward Island about 18 months ago (see CIDRAP Report Canada reports first H5N5 avian flu in a mammal).

Starting last spring we began to see increased reports of H5N5 (see WAHIS: More Reports of HPAI H5N5 in Canada), and last July, in Cell Reports: Multiple Transatlantic Incursions of HPAI clade 2.3.4.4b A(H5N5) Virus into North America and Spillover to Mammals, researchers reported finding the mammalian adaptive E627K mutation in a number of samples.

They wrote:

Thus, while A(H5N5) viruses are comparably uncommon, their high virulence and mortality potential demand global surveillance and further studies to untangle the molecular markers influencing virulence, transmission, adaptability, and host susceptibility.

Last May H5N5 was detected in Quebec Province, and this month it has been reported in both Ontario and Nunavut Territory (see map above). While these are sporadic sightings in wild birds, given the paucity of testing - particularly in remote regions - this subtype is probably more widespread than we know.

On the other side of the Atlantic, particularly in the UK and Northern Europe, HPAI H5N5 has been making inroads as well.

Recent examples include Norway Veterinary Institute Reports 1st Outbreak of HPAI H5N5 In Domesticated Birds and UK: HPAI H5N5 Rising (wild birds & poultry outbreak).

A recent DEFRA publication stated:

After a quiet summer with no reported H5N5 cases in northern Europe, October has seen a south-east spread of HPAI H5N5 cases in wild birds through Great Britain and on to the coast of Belgium (a common gull) and Germany (an auk species). In the north, Iceland has reported four wild bird H5N5 cases (1 black-headed gull and 3 ravens) and along the north coast of Norway there have been 5 wild bird H5N5 cases (4 gulls and 1 eagle) according to Animal Disease Information System (ADIS) - European Commission (europa.eu). 

And a quick look at WOAH's WAHIS dashboard shows notifications by no less than 10 updates from  8 countries (UK, Canada, Norway, Iceland, Faeroe Islands, Germany, Belgium, & Japan) on new or ongoing detections of H5N5 since October 1st.  

Whether this turns out to be a significant trend is something we'll have to wait to see.  

H5N5 has tried before, and failed to gain traction against a more biologically `fit' H5N8 virus. 

But that was then, and this is now.  Influenza's ability to continually reinvent itself via reassortment means that we can never assume that the flu threat of tomorrow will match the flu threat of today.