#17,767
HPAI H5N1 - like all influenza A viruses - undergoes continual evolution, including small changes from antigenic drift, and much larger changes from reassortment (see graphic above), also known as antigenic shift.
Three days ago, in Netherlands Reinstates Nationwide Poultry Lockdown Following Two H5N1 Outbreaks, we looked at the first outbreak of avian flu in the Netherlands since last July.
Overnight Wageningen University & Research (WUR) announced that sequencing of the virus behind this outbreak shows that it is a new reassortant virus, having picked up a new PB1 segment from a LPAI donor virus.
This reassortant virus still shows `strong similarity' to recent H5N1 viruses in the region, but it isn't clear if any of its properties (pathogenicity, transmissibility, host range, etc.) have changed.
The link and (translated) excerpts from the WUR report follow. I'll have a brief postscript after the break.
New variant of bird flu virus in Renswoude
Published on 16 november 2023
The bird flu virus that affected the laying farm in Renswoude is a new variant of the bird flu virus. The virus is related to the highly pathogenic H5N1 virus that has caused many outbreaks in poultry since 2021, but contains a new piece of genome - the so-called PB1 segment - from a low pathogenic virus. This is evident from genetic analysis of the virus by Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research).
On November 11, an outbreak of highly pathogenic avian influenza was diagnosed in Renswoude . This was the first outbreak since July of this year, after which an outbreak in poultry was also diagnosed on November 14 at a care farm in Middelie , and on November 15 at a petting zoo in Zaandijk .
New variant of the virus
WBVR examined the virus and showed that it is again a highly pathogenic H5N1 virus. Further research into the genetic composition of the virus in question shows that this is a new variant. The virus has acquired a new PB1 segment by reassortment with a low pathogenic virus. “The virus in Renswoude has a new genetic composition, but shows a strong similarity to the virus that has caused many outbreaks since 2021,” said WBVR researcher Nancy Beerens, head of the national reference laboratory for Avian influenza.
(SNIP)
Biosafety
The shelter-in-place requirement has been in force nationally again since November 14. The fact that the virus is genetically similar to the virus that caused many outbreaks in 2021-2023 and is found in wild ducks and geese is of concern. It is currently not known how pathogenic or contagious the new virus variant is for poultry. Biosecurity measures on poultry farms remain very important for proper prevention and control of the bird flu virus.
HPAI H5 continues to diversity into new clades and subclades as it spreads around the world, spinning off subtypes (H5N1, H5N5, H5N6, etc.), and generating scores of new genotypes.
Rather than having one worrisome H5 virus on our radar, there are literally dozens circulating at any given time.
Most will never amount to anything, being unable to compete with the more biologically `fit' viruses in the wild, but nearly every big advance made by the virus over the past 2 decades was preceded by a fortuitous reassortment event (see H5N1: The Only Constant is Change).
Whether today's announced reassortment is merely a footnote in the evolutionary history of H5, or something of more import, remains to be seen.
But avian flu will keep rolling the genetic dice, and we need to be prepared for the day that it gets `lucky'.
