WUR: New Variant of Bird Flu Virus Found at Poultry Farm Biddinghuizen

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Although the use of the word `new' regarding genotype BB of H5N1 is a little misleading (it has been seen in wild birds, mostly gulls), today's report from Wageningen University & Research appears to be the first time it has been confirmed in poultry flock. 

As H5N1 clade 2.3.4.4b continues to evolve it frequently `borrows' gene segments from other flu viruses (see graphic above), creating new genotypes.  Over the past 6 months a new reassortment, genotype BB, has become the dominant variant in European birds. 

According to the latest ECDC Surveillance Report: Avian influenza overview April – June 2023:

Six main genotypes corresponding to more than 98% of the HPAI A(H5N1) characterised viruses (> 1300) from 22 European countries have been identified since October 2022.

Four of these genotypes have been circulating in Europe since the 2021–2022 epidemiological year, while the others have newly emerged, very likely from reassortment events with avian influenza viruses circulating in Eurasian wild bird populations.

Between October 2022 and January 2023, the majority of the characterised viruses belonged to the AB genotype (H5N1- A/duck/Saratov/29-02/2021-like).

However, a rapid increase in the number of detections of the BB genotype (H5N1-/Herring_gull/France/22P015977/2022-like) was observed starting from December 2022. Since February 2023, the BB genotype has become the most frequently identified variant, reaching in April–May 2023 a frequency of about 90%, based on the data available.

First stop, the report from WUR, after which I'll have a bit more.

New variant of bird flu virus found at poultry farm Biddinghuizen

Published on July 31, 2023

The bird flu virus that hit the organic laying farm in Biddinghuizen (the Netherlands) turns out to be a new variant of the H5N1 virus. Genetic analyses by Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research) shows the virus found is the so-called BB genotype. This bird flu variant currently circulates among black-headed gulls.

On 24 July, an outbreak with highly pathogenic avian influenza was detected in Biddinghuizen (in Dutch). This is the first outbreak since February of this year, and the first after the confinement obligation was lifted by the Ministry of Agriculture, Nature and Food safety.

New variant

WBVR investigated the virus and proved the farm was hit by the highly pathogenic H5N1 virus. Further research into the genetic composition of the virus shows that this particular virus is a new variant. “The virus that was found in Biddinghuizen has a different genetic make-up than the virus detected on poultry farms earlier in the year,” said Nancy Beerens, head of the National Reference Laboratory for Avian Influenza.

The virus found in Biddinghuizen is referred to as genotype BB. "This virus is currently circulating mainly among black-headed gulls in the Netherlands and Europe and results in large mortality among these birds.” The specific HPAI H5N1 virus genotype BB contains three pieces of genome that come from gull viruses; the PA, NP en NS segments are derived from a H13 bird flu virus. 

“The contamination of the laying farm in Biddinghuizen shows that this variant of the bird flu virus can infect not only gulls but also poultry.” Previously, it was experimentally demonstrated in Italy that the gull variant of the bird flu virus also led to infections in poultry.

Biosafety

The obligation to confine poultry has been lifted in most regions in the Netherlands. According to the Dutch expert committee on bird flu, the risk of infection with the bird flu virus is still low to moderate (in Dutch). Biosecurity measures on poultry farms remain of great importance for proper prevention and control of the avian influenza virus.

Influenza A's super power is its ability to continually reinvent itself. As a segmented virus with 8 largely interchangeable parts, the flu virus is like a viral LEGO (TM) set which allows for the creation of thousands of unique variants.

Complicating matters even further, within these gene segments their can be unique amino acid changes (e.g. PB2-D701N, PB2-Q591K, PB2-E627K, etc) that can alter the behavior - and host range - of the virus.

The rapid rise of genotype BB over the past 6 months illustrates how quickly the avian flu landscape can change.   

It is now August, and birds that spent their summer in their high latitude breeding spots will soon begin their annual southbound migration.  With them, they may very well carry new reassortments, consisting of both new genotypes and new subtypes (e.g. H5N5, H5N7, H5N9, etc.). 

While we've not seen a truly successful mammalian adaption, the virus continues to try out new genetic combinations at an increasing rate.  And it only has to get lucky once.