Credit ECDC
#19,316
While our knowledge of the subtypes of influenza pandemic viruses prior to 1918 is admittedly murky - historical and serological reconstructions (as depicted in the above pandemic timeline produced by ECDC) - suggest that an H3 virus, possibly H3N8, circulated globally around 1900.This fits nicely into the H1, H2, H3 pattern of known influenza pandemic viruses going back nearly 140 years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?)What is certain is that roughly seventy years later an avian H3 virus ressorted with seasonal H2N2 and produced another pandemic in 1968, and its descendents have remained in circulation for nearly 6 decades.
Since then we've also seen:
- An equine H3N8 virus jump to dogs in 2004, followed three years later by an avian H3N2 virus in South Korea, with both reassorting with other subtypes (see J. Virology: Zoonotic Risk, Pathogenesis, and Transmission of Canine H3N2).
- An avian H3N8 virus was found in marine mammals (harbor seals) in 2011, and 2012’s mBio: A Mammalian Adapted H3N8 In Seals, provided evidence that this virus had recently adapted to bind to alpha 2,6 receptor cells, the type found in the human upper respiratory tract.
- In 2015's J.Virol.: Experimental Infectivity Of H3N8 In Swine, we saw a study that found that avian (but not canine or equine) H3N8 could easily infect pigs.
This led to 2023's EID Journal: Evolution of Avian Influenza Virus (H3) with Spillover into Humans, China, where researchers described finding 4 sub-lineages and an astonishing 126 genotypes of avian H3 viruses circulating in China.
The authors also described a recent reassortment event where H3N8 acquired the internal genes from LPAI H9N2, a promiscuous virus which had previously contributed genes to both H5N1 and H7N9 (see PNAS: Evolution Of H9N2 And It’s Effect On The Genesis Of H7N9).
Vet. Research: Emergence of a Novel Reassortant H3N3 Avian Influenza Virus with Enhanced Pathogenicity and Transmissibility in Chickens in China
Transboundary & Emerg. Dis.: H3 Avian Influenza Virus Isolated from China in 2021–2022 Showed the Emerging H3N8 Posed a Threat to Human Health
Eurosurveillance: Analysis of Avian Influenza A (H3N8) Viruses in Poultry and their Zoonotic Potential
All of which serves as prelude to the following report - again from China - describing another migratory-bird-origin H3N8 subtype AIV - isolated and identified in Jiangsu Province in 2024 - that has also acquired a number of mammalian–adaptive mutations, exhibits dual receptor–binding capacity, and has cross-species transmission potential.
Due to its length, and technical nature, I've only posted the link, abstract, and some excerpts from the discussion. Follow the link to read it in its entirety. I'll have a bit more after the break.A Multi-Reassortant H3N8 Avian Influenza Virus Derived From Migratory Birds in Eastern China Exhibits Cross-Species Transmission Potential
Yunfei Guo, Zhonglong Yang, Hui Yang, Xinyu Miao, Tao Qing, Daxin Peng, Sujuan Chen
First published: 30 August 2026
https://doi.org/10.1155/tbed/9889145Digital Object Identifier (DOI)
Abstract
Migratory birds are one of the main reservoirs and long-distance transmission vectors of avian influenza viruses (AIVs). A migratory-bird-origin H3N8 subtype AIV (A/wild bird/Huadong/sy17/2024, hereafter named as WD/HDsy17/24) was isolated and identified in Jiangsu Province, Eastern China, in 2024. However, few studies have been conducted on the cross-species transmission potential of H3N8 AIVs from migratory birds.Phylogenetic analysis indicated that the eight gene segments of WD/HDsy17/24 originated from different subtypes of AIV such as H3N8, H1, H5N1, H5N2, and H7N7 and was a multirecombinant virus. WD/HDsy17/24 virus showed a binding affinity to both SAα-2, 3-galactose (Gal) and SA α-2, 6 Gal receptors, relatively weak thermal stability and pH stability.The SPF chicken pathogenicity indicated that the virus only causes mild respiratory symptoms and leads to lung hemorrhage and congestion. The mice pathogenicity indicated that the body weight of infected mice drops to the lowest value on the third day after infection, the lung-to-body ratio significantly increases, and inflammatory or edema lesions appear in the lungs.Moreover, this virus can infect guinea pigs through contact transmission and aerosol transmission routes from infected SPF chickens. After infection, obvious secretions can be seen in the eyes of guinea pigs. In the contact transmission group, viral shedding was detected in the nasal wash of one guinea pig at 6 days postinfection (dpi). In the aerosol transmission group, viral shedding was detected in the nasal washes of one guinea pig at both 10 and 12 dpi and in another guinea pig at 14 dpi. After 21 days, the seroconversion rate of serum antibodies in both groups is 100%.These findings underscore the need for continued surveillance of H3N8 viruses to identify circulating strains that may potentially threaten human health.
(SNIP)
Discussion
As a natural reservoir, wild birds facilitate transregional and cross-national transmission [28]. H3N8 AIVs, a dominant subtype in wild birds, have a broad host range, infecting poultry [29] and crossing species barriers to infect horses, dogs, pigs, and humans [30–33]. Therefore, long-term surveillance in wild bird migration areas is urgently needed.
Recent reports have documented novel reassortant H3N8 variants isolated a reassortant H3N8 from a wild bird in Jiangxi has become widespread in Chinese chicken flocks, forming a triple-reassortant genotype [5, 10]. The isolate WD/HDsy17/24 also displayed multi-reassortant characteristics, with eight gene segments derived from reassortment of H1, H3N8, H5N1, H5N2, and H7N7 influenza viruses. This is consistent with a broader analysis showing that wild-bird-origin H3N8 in China evolved into at least 126 genotypes from 2009 to 2022, with genotype G25 (reassorted with H9N2) capable of infecting chicken and crossing to humans [34]. The close genetic relationship of our isolate’s M and NS genes to H9N2 AIVs suggests enhanced host adaptability via reassortment.
(SNIP)
In summary, through analysis of the genetic evolutionary characteristics and pathogenicity of a wild-bird-origin H3N8 AIV from eastern China in 2024, this study confirmed that the strain carries multiple mammalian–adaptive mutations and exhibits dual receptor–binding capacity and cross-species transmission potential.The findings provide important experimental data for the early warning, surveillance, risk assessment, and control strategy development of H3N8 AIVs and are of great significance for mitigating their potential public health risks.
While this latest H3N8 paper doesn't identify a new pandemic strain, it does add to what has become difficult to ignore; that the panoply avian H3 viruses in China have become increasingly diverse, they continue to evolve rapidly, and some have already displayed worrisome mammalian adaptations.
As any kid with an erector set can tell you, the more interchangeable parts you have, the more neat stuff you can build. The same holds true for influenza reassortment - the more gene segments available for swapping - the more novel subtypes/genotypes that are possible.
While that doesn't guarantee an untoward outcome, this trend has obviously captured the attention of Chinese researchers, and should be on our radar as well.