Swine Flu Strain Jumps from Humans to Pigs Nearly 400 Times

Jul 31, 2023

By Jean-Paul MacDonald

A new study focusing on the pdm09 virus, responsible for the 2009 H1N1 pandemic, has uncovered eye-opening information. Since 2009, pdm09 has been transmitted from humans to swine approximately 370 times, posing significant concerns for managing influenza A infection in individuals working with pigs.

Influenza A is a virus that can cause the flu in humans, birds, swine, and certain other mammals. The pdm09 virus, responsible for the 2009 pandemic that claimed many lives worldwide, has shown a consistent pattern of passing from humans to swine since the pandemic. As the virus circulates among swine, it undergoes evolutionary changes that could enable it to infect humans again.

To gain a deeper understanding of this risk, researchers led by Alexey Markin from the U.S. Department of Agriculture-Agricultural Research Service conducted a detailed analysis of pdm09 transmission data from 2009 to 2021. Their objective was to assess how these interspecies events impacted the genetic diversity of the virus in swine and the potential risk of human infection.

The analysis revealed approximately 370 separate instances of pdm09 transmission from humans to swine since 2009, with most of these events occurring when the virus was highly prevalent among humans. Even during the COVID-19 pandemic in 2020 and 2021, when pdm09 circulation in humans declined, it persisted in swine due to approximately 150 human-to-swine transmissions between 2018 and 2020.

Most of the time, when the flu passed from humans to pigs, it didn't spread further. But sometimes, it kept moving among pigs in the U.S. These pig strains were different from the ones in human flu vaccines, so the vaccines might not fully protect people. The study also found that at least five times, the flu went from pigs back to humans.

These discoveries show that it's very important for people who work with pigs to be careful about the flu. If they take precautions, it can stop the flu from spreading to pigs and make sure there are fewer different types of flu in pigs. This helps lower the chances of new viruses forming and makes it less likely for pigs to pass the flu to humans.

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