One of the more worrying aspects of HPAI H5 - particularly among Clade 18.104.22.168 viruses - is their ability to reassort with other (usually low path) viruses and reinvent themselves into new genotypes (retaining both their HA and NA gene) or even new subtypes (swapping out their NA and usually some internal genes).
We saw this happen in North America in our 2014-15 HPAI H5 epizootic, when H5N8 spawned both H5N2 and a North American version of H5N1 (see USGS: Genetic Analysis Of North American Reassortant H5N1 Virus From Washington State) and again last year in Europe with the generation of H5N5 and H5N6 during their epizootic (see CIDRAP: Greek H5N6 Virus Appears Distinct From Asian Strain).
Events that led Germany's Friedrich-Loeffler-Institut (FLI) to repeatedly warn last winter and spring that:
`Generation of reassortants always must be expected when different high and low pathogenic influenza viruses are circulating in one population.'We've seen HPAI H5N6 generate dozens of genotypes as it has spread across China, Japan, and South Korea (see Virology: Five Distinct Reassortants of HPAI H5N6 In Japan - Winter 2016–2017) and the emergence of additional genotypes is to be expected.
Today, however, we've a bit of a twist in that the HPAI H5N6 virus detected in South Korea a week ago (see South Korea: MAFRA Confirms HPAI H5N6 At Gochang Poultry Farm) turns out NOT to be a reassorted H5N6 virus, but rather a new reassortment of Europe's H5N8 virus and LPAI H3N6.Details are scant at this hour, but we have a brief announcement from South Korea's Animal and Plant Quarantine Agency (APQA), and an English language news report.
The duck AI AI (H5N6) virus in Gochang is estimated to be a new type of virus
Department Agriculture, Forestry and Livestock Quarantine Office Writer Yihyeonjik 14 2017-11-27
It is estimated that a new type of virus has been introduced into the duck AI (H5N6) virus.
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We get considerably more detail from the following Yonhap news report:
The latest bird flu outbreak in South Korea is presumed to be a new type of avian influenza strain that is a reassortment of highly pathogenic strains that spread in Europe last year, the quarantine authority said Monday.By Yonhap
- Published : Nov 27, 2017 - 14:08
The Animal and Plant Quarantine Agency said its interim inspection into the bird flu case in Jeolla Province on Nov. 17 may have been transmitted from migratory wild birds that have flocked to the nation since October.
"A new strain generated by virus reassortment is presumed to have entered the nation since October via winter migratory birds," the APQA said in a briefing. "A joint investigation team has been analyzing viruses separated from 852 corpses and droppings of wild birds to figure out the cause of the outbreak and trace its origin."
The genomic analysis into the cases showed a new type of H5N6 strain, which arose from the reassortment between a high pathogenic
H5N8 that spread in Europe in late 2016 and a low pathogenic H3N6 virus found in European wild birds, the APQA agency said.
The irony here is Europe had been warned to watch for the arrival of HPAI H5N6 from Asia this winter via migratory birds (see Germany: FLI Risk Assessment On Return Of HPAI H5 Avian Flu) and instead a reassorted H5N6 virus appears to have emerged from European birds, and has turned up for the first time in Korea.
Once again, avian flu has zigged when everyone expected it to zag.It isn't clear at this time what risks - beyond a threat to poultry - this new reassortant virus poses. Its European parentage might reduce its risk to humans over that posed by reassortants from the Asian H5N6 virus, but it is far too soon to say.
Between overlapping global flyways, increasingly efficient carriage via migratory birds, and the ability to reinvent themselves through reassortment, novel flu viruses are a formidable and highly unpredictable foe.
A reminder that we need to remain alert, get better prepared, and resign ourselves to be surprised by whatever our growing array of novel flu viruses throws at us next.