The new study shows that the virus has passed from humans to swine about 370 times since 2009, this has subsequently resulted in the evolution of other variants that then jumped from swine to humans.
Influenza A can cause the flu in humans, birds, swine, and some other mammals. In 2009 and 2010, a pandemic caused by pdm09 resulted in thousands of human deaths around the world. Since then, as demonstrated in prior studies(), pdm09 has repeatedly passed from humans to swine, and circulation of the virus among swine leads to evolutionary changes in pdm09 that could make it more likely to cross back and infect humans.
The recent analysis showed that most of the swine-to-human transmission events occurred when the pdm09 burden was highest among humans. In 2020 and 2021, during the COVID-19 pandemic, pdm09 circulation among humans dropped, but pdm09 circulation persisted in swine as a result of about 150 human-to-swine transmissions between 2018 and 2020.
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The researchers found that most human-to-swine transmission events were isolated, but a few led to the sustained circulation of different pdm09 genetic lineages among swine in the U.S. These swine-circulating variants appeared to be genetically poor matches for human seasonal vaccines, suggesting that the vaccines would have provided scant protection against them.
These findings add to mounting evidence that managing influenza A infection in people who work with swine can help prevent transmission to pigs, and subsequently reduce the risk of spread back to humans().
Controlling influenza A virus infection in humans can minimize the spillover of viruses into pigs and reduce the diversity of viruses circulating in swine populations. Limiting virus diversity in pigs can minimize the emergence of novel viruses and the potential for swine-to-human transmission of influenza A virus.
References:
- Anderson, Tavis K et al. Swine Influenza A Viruses and the Tangled Relationship with Humans. Cold Spring Harbor Perspectives in Medicine vol. 11,3 a038737. 1 Mar. 2021.(https://perspectivesinmedicine.cshlp.org/content/11/3/a038737)
- Markin A, Ciacci Zanella G, Arendsee ZW, Zhang J, Krueger KM, Gauger PC, et al. Reverse-zoonoses of 2009 H1N1 pandemic influenza A viruses and evolution in United States swine results in viruses with zoonotic potential. PLoS Pathog. 2023.(https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1011476)
Source: Eurekalert
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