Although less common, any virologist will tell you that `Shift happens'.
While we generally think of reassortment happening in birds, pigs, or humans, over the past 20 years we've learned that the host range of influenza is much larger than we thought. Today marine mammals, mink & foxes, rodents and even companion animals like dogs and cats are on our watch list (see graphic above).
Since then we've seen multiple reports of influenza viruses in dogs (mostly from Asia), many involving novel reassortments:While once believed unlikely hosts, dogs are now increasingly on our radar. In 2007 we learned that an avian H3N2 virus (from chickens and doves) had jumped to dogs in South Korea (see Transmission of Avian Influenza Virus (H3N2) to Dogs).
Canine H3N2 Reassortant With pH1N1 Matrix Gene
Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China
Korea Finds More Dogs With H5N8 Antibodies
Influenza A(H6N1) In Dogs, Taiwan.
While the H3Nx virus appears to be on its own worrisome trajectory in dogs (see One Health Adv.: Surveillance & Characterization of Avian-origin H3N2 Canine Influenza Viruses (China 2021)), since the emergence of a more mammalian-adaptable HPAI H5 clade 2.3.4.4b virus, we've also seen an increase in those reports as well.
J. Virulence: HPAI H5N1 Virus Infection In Companion Animals
Eurosurveillance: Asymptomatic infection with clade 2.3.4.4b HPAI A(H5N1) in carnivore pets, Italy, April 2023
Italian MOH Statement: H5N1 Seroconversion In Dogs & Cats On Affected Poultry Farm In Brescia
Canada CFIA & PHAC: Domestic Dog Tests Positive for Avian Influenza in Canada
Although the practice is not as common as it once was, the farming of of dogs for human consumption still exists in parts of Asia, and these farms - much like with the fur trade - have been shown to be hot spots for the spread, and evolution, of novel influenza viruses (see China: Avian-Origin Canine H3N2 Prevalence In Farmed Dogs).
Last October the Journal of Infection published an intriguingly titled report called Emergence of a novel reassortant H5N6 subtype highly pathogenic avian influenza virus in farmed dogs in China by Xin-Yan Yao , Chun-Yang Lian , Zhi-Hang Lv , Xue-Lian Zhang , & Jian-Wei Shao.
Sadly, this report is behind a pay-wall, no abstract is provided. But it is referenced in the opening line of today's report from Chinese researchers describing the discovery of a Triple (Avian/Canine/Human) reassortant HPAI H5N6 virus (see graphic below) detected in wild birds in Shenzhen Province in March of 2023.
Six of the eight gene segments (HA,PB2, PB1, PA, NP, NS) in this Clade 2.3.4.4b1 virus (a Canine offshoot from avian clade 2.3.4.4b) appear to have come from that H5N6 Canine virus (A/canine/China/GX30/2023, the NA comes from an avian source (A/duck/Sichuan/SC5698/2021 (H5N6)), and the M gene is a 99.49% match to a human infection with H5N6 in Guangdong Province in 2021 (A/Guangdong/1/2021(H5N6)).
Genetic analysis reveals this triple reassortant virus retains a high affinity for binding to the avian-type receptors (226Q and 228G) along with enhanced binding to the human-type receptors (S137A and T192I).
While the impact of this novel reassortment remains to be seen, it has some of the worrisome genetic traits we look for, and is a reminder how just how dynamic HPAI H5's evolutionary process has become.
You'll find the link, and excerpts (reformatted for readability) from the report below. I'll have a brief postscript after the break.
Emergence of a triple reassortment avian influenza virus (A/H5N6) from wild birds
Yan-kun Ke 1, Xin-yu Han 1, Si-ru Lin, Rong-qi Liu, Ming Liao, Wei-xin Jia
Open Access Published:January 17, 2024 DOI:https://doi.org/10.1016/j.jinf.2024.01.005
Dear Editor,
A recent publication in this Journal reported the emergence of an H5N6 strain originating from farm dogs in China 1. H5N6 subtype avian influenza strains in Clade 2.3.4.4 have circulated in poultry in China since 2013 2. In 2014, highly pathogenic avian influenza H5 GsGd (Clade 2.3.4.4) caused multiple outbreaks on several continents. 3. Studies have shown that H5N6 AIV can infect not only poultry and wild birds, but also mammals such as pigs, cats, and even humans.
China has adopted a vaccine immunization policy to prevent the spread and prevalence of influenza viruses among poultry. However, this strategy does not prevent the spread and evolution of influenza viruses in waterfowl, wild birds and mammals4,5. Avian influenza viruses carried by wild birds can not only cause avian influenza outbreaks but also infect companion animals that go outdoors, as in the case of dogs in Guangxi1,6. Therefore, monitoring avian influenza viruses carried by wild birds has become important.
In the course of avian influenza surveillance at the wild bird interface in the Pearl River Delta region, our laboratory isolated a wild-bird-derived H5N6 subtype AIV strain from wild bird fecal samples collected in Shenzhen in March 2023. This strain was named A/wild bird/Guangdong/SZ1/230322/ H5N6.
We sequenced the whole genome of the virus and analyzed its genetic evolution. The HA phylogenetic tree showed that the isolate was located in Clade 2.3.4.4b1, which is in Clade 2.3.4.4b with the strains currently prevalent in poultry hosts on the live bird market and the vaccine strains currently found in China (Re-14 and rHN5801). SZ1 belongs to the same branch as the H5N6 strain originating from farm dogs reported by Yao et al. in GISAID in 2023.Genetic analyses showed that the cleavage site of the HA gene in A/Wildbird/Guangdong/SZ1/230322/H5N6 contained the contiguous basic amino acid REKRRKR↓GLF, which is consistent with the molecular profile of highly pathogenic strains.
The SZ1 strain has mutations in the HA gene at the S137A and T192I loci, a double-site mutation that results in enhanced binding of the virus to the α-2,6-linked SAs (human-type receptors), which is characterized by enhanced binding to the mammalian receptor. 226Q and 228 G indicated that these strains have an affinity for the avian-type receptors 7, 8. T33K, L89V, R477G, I495V, E627K, and 701D in the PB2 gene, L13P, D538, K578, and 614E in the PB1 gene, A150R and A184K in the NP gene, E133 and G631S in the PA gene, D97E in the NS gene, and N30D and T215A mutations in the M1 gene not only enhance receptor binding but also increase virulence in mammals9, 10.
BLAST of the GenBank database showed that the sequences of the HA and NA fragments observed in this study showed the highest nucleotide sequence identity with A/Canine/China/GX30/2023 (H5N6) and A/duck/Sichuan/SC5698/2021 (H5N6), 98.59% and 98.62%, respectively. The sequences of the NS, PA, PB2, and PB1 fragments of the internal genes were similar to the canine-derived virus from Guangxi, China. The nucleotide similarity between the M segment sequence and the human source sequence from Guangdong, China, was 99.49% (Table S1). Fig. 2 shows a schematic diagram of the triple reassortment of human, canine, and avian gene fragments it carries.
(SNIP)
In summary, the wild-bird-origin H5N6 strain SZ1 isolated in Shenzhen in this study belonged to Clade 2.3.4.4b1 as well as the virus currently prevalent in China. The strains have similar antigenic properties. Analysis of the key HA gene loci showed that the SZ1 strain retained both high affinity for binding to the avian-type receptors (226Q and 228 G) and enhanced binding to the human-type receptors (S137A and T192I).
Whole gene sequence comparison analyses revealed that the HA, NP, NS, PA, PB1, and PB2 gene fragments of the SZ1 strain were all highly similar to H5N6 isolated from Guangxi farm dogs and the M gene was highly similar to the human strain, suggesting that highly pathogenic H5N6 strains carried by wild birds have the potential to be transmitted to outdoor mammals.
Shenzhen is an important stopover, sometimes referred to as a “transit refueling station,” on the Siberian–Australian wild bird migration route, and thus attracts many migratory birds every winter. Wild bird migration routes are an important means of influenza virus transmission and play an important role in the spread and evolution of the virus. Therefore, it is crucial to improve the continuous monitoring of wild bird migration routes.
The good news is these genetic gymnastics occurred in the wild a year or more ago, and so far, we haven't seen any abrupt change in the the behavior of HPAI H5.
But they do add additional diversity to the array of genetic building blocks available for future reassortments, meaning they may have a more important role to play down the road.
