Something Winged This Way Comes

#18,241

Prior to 2021, North America only had one brush with HPAI H5; an avian epizootic that began in December of 2014 and eventually infected poultry in 15 states.  

That H5Nx virus, however, was ill-suited for long-term carriage in wild and migratory birds, and disappeared the following summer (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).

Since then, HPAI H5 has undergone many changes (via reassortment), has switched from an H5N8 to an H5N1 subtype, and has greatly expanded both its mammalian and avian host ranges.  

It now persists (at low levels) in wild birds even through the summer months, and new waves of infection are expected when migratory birds return from their high latitude nesting places this fall. 

Exactly what returns this fall is unknown, as the virus has had numerous opportunities to reassort or mutate over the summer.  We could see something worse, or if we get very lucky, an attenuated threat (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1).

It is also possible that other subtypes - such as H5N5 or H5N6 - will play a bigger role this winter (see Cell Reports: Multiple Transatlantic Incursions of HPAI clade 2.3.4.4b A(H5N5) Virus into North America and Spillover to Mammals).

The ability to continually reinvent itself is influenza A's superpower.  And as avian H5Nx conquers more of the world, it has increased opportunities to reassort with new viruses, producing diverse offspring with unpredictable impacts.  

As the graphic at the top of this blog indicates, the fall migration has already begun in North America, although it won't peak for several months.  This is, however, the time of year when poultry producers - and others - should be increasing their biosecurity efforts. 

One of the publicly available tools that we can use to track bird migration comes from the Birdcast.info website, which uses weather radar, and advanced forecasting methods to track birds. This website is a joint venture by The Cornell Lab, Colorado State University, and U Mass Amherst, and supported by a large number of partners. 

The graphic and news story below - from October of 2023 - shows > 1 billion birds on the move in a single night. 

This is a fascinating website, with much to explore.  Highly recommended. 

As to what this fall's migration will bring, only time will tell.  Perhaps a respite.  Perhaps another curve ball.  

Like the incoming tide, we can't stop this annual natural event. We can only try to find ways to mitigate its impact.