In the Northern Hemisphere uncounted millions of migratory birds spend their summers roosting in high latitude breeding spots, just below the Arctic circle. They go there for the abundant insect food supply, cooler weather, and a safe place to hatch their young.
These birds come from all over the globe, some traveling many thousands of miles. Invariably a few will pick up and carry strains and subtypes of avian flu (both LPAI and HPAI) with them.Until recently, it appeared that an innate immunity to low path avian flu viruses prevented high path (HPAI) viruses from persisting for very long in migratory bird populations. Outbreaks and the carriage of these more dangerous viruses was therefore self-limiting (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
Last year's dual epizootics in Asia (H5N8 & H5N6) and Europe (H5N8) - both exhibiting enhanced persistence and expanded host ranges - have raised concerns that HPAI viruses are becoming better adapted to migratory birds.Since birds can be co-infected by more than one flu virus, the potential for further reassortment (see graphic below) - producing new genotypes of existing subtypes, or potentially even new subtypes - can't be ignored.
When you add in the recent evolution of LPAI H7N9 into an HPAI virus in China, and its rapid spread via migratory birds, the question becomes - what might we expect to return with migratory birds this fall?
Since the only constant with influenza viruses is change, and the recent crop HPAI H5 viruses have shown unusual promiscuity - generating multiple offshoots like H5N5, H5N3, H5N2, etc. - there's simply no way to know.But as the following story from Scotland's national newspaper The Scotsman explains, Ian Brown, head of virology at of the UK’s Animal and Plant Health Agency (APHA) is more than a little concerned.
By Brian Henderson
Published: 08:46 Wednesday 06 September 2017
Scotland’s poultry producers should prepare themselves for a potential new strain of avian influenza reaching Europe’s poultry farms this winter, a leading disease expert has warned.
Ian Brown, head of virology at of the UK’s Animal and Plant Health Agency (APHA), told the World Veterinary Poultry Association conference that there was a likelihood that avian flu would return to Europe over the next few months.
And if the strain was different to one we had seen before – which was possible – it could have significant implications on the poultry industry, he warned.
Brown said while the situation was currently uncertain, it was important poultry keepers were prepared against a potential biosecurity risk.
(Continue . . . .)
Up until four years ago, we really only had one HPAI virus of great concern; H5N1. Since then the number of worrisome HPAI subtypes have grown, and we now have multiple genotypes and clades of H7N9, H5N6, and H5N8 to contend with.
The complexity and diversity of avian flu viruses around the world continues to rise, and so does the threat level.Add in the growing number of swine flu viruses, canine H3N2, and a smattering of `oddball' (bat, mink, seal, raccoon) flu viruses, and you begin to understand why the CDC's IRAT (Influenza Risk Assessment Tool) list of novel flu subtypes/strains with some degree of pandemic potential has doubled in size since 2011.
None of this guarantees a repeat of last winter's European and Asia epizootics, or the emergence of something worse. But the necessary ingredients appear to be available, and so the prudent course is to assume a return until proven otherwise.