#18,884
Normally, our concern with the cross species transmission of flu viruses between birds and pigs is that an avian flu strain will jump to swine (see graphic above) and reassort into a more mammalian adapted virus.
But today, we have a detailed report on the opposite. A swine H1N2 virus jumping from pigs to turkeys (and infecting a human), in France.
In 2020, a new swine H1avN2#E virus appeared in pigs in Brittany and rapidly become dominant (see ANSES Reports A `New' Swine Flu Virus Has Taken Over Other Genotypes in France).
Around the same time, this swine virus was also reported in adjacent turkey farms. This excerpt from the aforementioned ANSES report:
In addition to the impact on the pig sector, the emergence of a new variant may also increase the risk of transmission to other animal species and to humans. “The H1avN2#E virus has caused several outbreaks of infection on turkey farms since 2020 and was responsible for a serious human case of swine flu in 2021.
Human exposure to swine influenza viruses increases the risk of reassortment with a human flu virus, which could lead to the emergence of a virus that is better adapted to humans. As pigs are also susceptible to human and avian influenza viruses, these animals can end up being mixing vessels for viruses. The last flu pandemic, which occurred in 2009, was caused by a swine influenza virus” underlines the scientist.
Just over 4 years ago, in Santé Publique France: Novel H1N2v Flu Infection In Côtes d'Armor, Brittany we looked at the first detection of what was then described as - an influenza A (H1N2) v clade 1C virus. 2.4 of porcine origin - in a man living near swine farms in Northwest France.
Somewhat confusingly, while these swine/turkey and human swine variant viruses have different names, they are actually closely related (see graphic below). Naming conventions are not standardized between public health and veterinary research.
But for convenience sake, we'll stick to the H1avN2#E genomic designation in today's blog.
Interestingly, the authors consider the possibility of short-or-medium distance airborne spread between farms (see Revisiting the Environmental Persistence and Airborne Spread of HPAI H5), along with other routes; including the transport of pigs in open vehicles, movement of contaminated trucks, equipment and personnel, and possibly swine slurry.While the human case, and the spillover into turkeys, has been previously reported, we've a follow up report today on the evolution, and apparent (turkey) farm-to-farm transmission of this emerging swine virus.
The authors identified 9 different spillovers into turkey farms, and the subsequent spread to 10 other farms. They also identified a number of potential turkey adaptation markers; HA: E233K or E236K and NA: T401N and S416N.
While these viruses are obviously not ready for prime time - when you add the severe human infection from 2021- you have the basic ingredients for an emerging zoonotic threat.
Identification of H1N2 influenza viruses in turkeys after spillover from swine and in vitro characterization
Chloé Chavoix a d, Pascale Massin a, François-Xavier Briand a, Katell Louboutin a, Rachel Busson a, Florent Souchaud a, Gautier Richard b, Claire Martenot a, Aurélie Le Roux b, Edouard Hirchaud b, Yannick Blanchard b, Sophie Le Bouquin-Leneveu c, Axelle Scoizec c, Céline Deblanc b, Séverine Hervé b, Audrey Schmitz a, Eric Niqueux a, Gaëlle Simon b, Ronan Le Goffic d, Béatrice Grasland a
https://doi.org/10.1016/j.virusres.2025.199634
Under a Creative Commons license
Open access
Highlights
- Transmissions of a new H1N2 IAV from swine to turkey occurred in France.
- This virus might have been transmitted between turkey farms.
- E233K or E236K on HA, T401N and S416N on NA may be markers of adaptation in turkeys.
- Viruses showed slight differences across mammalian-origin cell lines.
- Eggs allowed more discrimination between viruses but were less efficient than cells.
Abstract
Influenza A viruses (IAVs) circulate among animals and humans and can cross species barriers to adapt to new hosts. In France, since 2020, a new genotype named H1avN2#E has predominated in pig farms. In parallel, this virus was detected in 19 breeding turkey flocks and in a human case, indicating interspecies transmission.
The objectives of this study were (i) to analyze viral sequences detected in turkeys between April 2020 and January 2023 and compare them with swine sequences to identify potential markers of adaptation and (ii) to characterize three representative viruses in vitro and in ovo on MDCK, MLE15 and A549 cells, as well as on embryonated chicken eggs.
Results suggest that following initial swine-to-turkey spillovers, the virus circulated between turkey farms. Phylogenetic analyses and host origin guided the selection of three viruses: a reference swine virus (A), a turkey strain closely related to swine viruses (B) and a virus apparently circulating in turkeys (C). Three molecular markers may contribute to turkey adaptation: the E233K, under positive selection pressure, or E236K mutations in the 220-loop of the receptor-binding site of HA protein and two NA substitutions, T401N in antigenic site 2d and S416N.
Replication kinetics showed that at low MOI (0.001), virus C produced more infectious particles on MDCK and A549 cells, whereas at high MOI (0.1), virus B produced more. In ovo, infectious particles were generated for viruses A and B but not efficiently for virus C, in contrast to mammalian cells where production was higher.
(SNIP)
In conclusion, this study demonstrated swine-to-turkey spillovers of the H1avN2#E virus, first identified in swine in 2020, and provided evidence of possible turkey-to-turkey transmission.
A glutamate-to-lysine substitution at positions 233 or 236 of the HA RBS 220-loop may represent an adaptation marker for turkeys. Similarly, NA substitutions T401N in antigenic site 2d and S416N may represent a feature associated with turkeys, despite the absence of detectable positive selection.
Viral and genomic replication kinetics revealed subtle differences among the three viruses, with the “Turkey virus” producing higher titers in MDCK and A549 cells at MOI 0.001 while the “Turkey-swine-like virus” yielded more at MOI 0.1. In embryonated chicken eggs, infectious particles were produced for the “Turkey-swine-like virus” and “Swine virus” but not efficiently for the “Turkey virus”.
Further characterization of these H1N2 viruses in additional host-derived cells and in vivo models would be needed to better capture the complexity of host-virus interactions.For more on the growing zoonotic threat from European swine flu viruses, you may wish to revisit last April's:
