Influenza A Viruses in Swine: A Complex Ecosystem Driving Viral Emergence and Zoonotic Threats

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Influenza A viruses (IAVs) are a constantly evolving and complex group of viruses with the potential to cross species boundaries and cause zoonotic diseases.

One key player in the emergence of novel IAV strains is the pig, which serves as a natural host for the mixing of gene segments between avian, swine, and human influenza viruses.

The resulting reassortment events can lead to the creation of new virus variants with unpredictable properties, including the ability to infect humans.

While the genomic diversity of swine-origin influenza A viruses (swIAVs) in Europe and North America has been extensively studied, there remains a significant gap in our understanding of swIAV populations in Southeast Asia.


The EA H1N2 influenza virus is a subtype of influenza A that emerged in 2009. It is a reassortant virus, meaning that it contains genetic material from two different influenza viruses: an H1N1 virus that circulated in humans in 1918 and an H3N2 virus that circulated in pigs in 1968.

The EA H1N2 virus has a number of characteristics that make it different from other influenza viruses.

First, it is more transmissible than other influenza viruses. This means that it is easier for the virus to spread from person to person.

Second, the EA H1N2 virus is more likely to cause severe illness, especially in young children, older adults, and people with underlying health conditions. Third, the EA H1N2 virus is less responsive to antiviral medications than other influenza viruses.

The EA H1N2 virus has had a significant impact on public health. In the 2009-2010 influenza season, the EA H1N2 virus caused a global pandemic. The pandemic resulted in an estimated 18,000-575,000 deaths worldwide. In the United States, the EA H1N2 virus caused an estimated 36,000 deaths.

The EA H1N2 virus continues to circulate in the human population. It is one of the most common strains of influenza virus that causes seasonal influenza. The EA H1N2 virus is also a potential threat for future pandemics.

There are a number of things that can be done to reduce the impact of the EA H1N2 virus on public health. These include:

  • Getting vaccinated against influenza every year.
  • Taking antiviral medications if you get sick with influenza.
  • Practicing good hygiene habits, such as washing your hands frequently and covering your mouth and nose when you cough or sneeze.
  • Staying home from work or school if you are sick with influenza.

By taking these steps, we can help to protect ourselves and our loved ones from the EA H1N2 virus.

In addition to the above, there are a number of other factors that can influence the spread and impact of the EA H1N2 virus. These include:

  • The level of immunity in the population.
  • The availability of antiviral medications.
  • The effectiveness of public health measures.
  • The severity of the season’s influenza virus.

This region is of particular interest due to its high biodiversity, dense human and animal populations, and close proximity to avian species, all of which contribute to the potential for interspecies transmission and viral evolution.

In a remarkable study that persisted despite the challenges posed by the COVID-19 pandemic, researchers conducted a comprehensive longitudinal influenza surveillance project in pigs across several major provinces in Cambodia. Spanning from March 2020 through July 2022, this study aimed to shed light on the dynamics of swIAV circulation and evolution in Southeast Asia.

The findings of this study revealed a diverse landscape of swIAV viruses circulating among pig populations in the region. Through meticulous genetic analysis, the researchers traced the evolutionary origins of these viruses and identified the mechanisms underlying their emergence.

Particularly, the researchers observed the acquisition of gene segments through reassortment events that had occurred across different geographical locations. This phenomenon was facilitated by both intercontinental and intracontinental spread of swIAV lineages, reminiscent of the process that led to the emergence of the H1N1/pdm09 virus in Mexico.

One remarkable discovery was the identification of a novel subtype of swIAV known as EA H1N2. This virus, with a unique genetic makeup, had likely emerged several years before its initial detection in Cambodia in 2021.

The EA H1N2 subtype carries a combination of gene segments from swine, human, and avian sources, highlighting the intricate and dynamic interplay between different influenza virus reservoirs. This discovery underscores the need for continuous vigilance and monitoring to understand the zoonotic potential and pandemic risk associated with such novel viruses.

The study’s implications extend beyond the realm of scientific discovery. The research underscores the critical importance of identifying emerging swIAV lineages early on.

The interconnected nature of global pig value chains plays a pivotal role in transmitting these viruses across regions and continents, fostering the emergence of new and potentially dangerous virus strains.

This interregional spread emphasizes the need for systematic and consistent surveillance efforts to mitigate the risks associated with novel virus emergence.

The study also highlights the dual threats posed by the constant evolution of swIAVs. Not only do these viruses maintain the potential to infect humans, but they also impact the swine industry, causing economic losses due to diseases such as porcine reproductive and respiratory syndrome and African swine fever. Given the rapid growth in meat consumption, particularly pork, across Asia, the economic stakes are high.

To address the challenges posed by evolving swIAVs, a paradigm shift in surveillance strategies is proposed. Traditional methods of individual animal sampling are resource-intensive and often inadequate for capturing the breadth of viral diversity. The study suggests the integration of metagenomic surveillance techniques, focusing on air and wastewater samples collected from farms and slaughterhouses. Coupled with automated analytical tools, this approach could rapidly provide insights into the spatiotemporal occurrence of a wide range of pathogens in both animals and humans.

In conclusion, the comprehensive longitudinal study conducted despite the obstacles of the COVID-19 pandemic has yielded invaluable insights into the dynamics of swIAV circulation, reassortment, and emergence in Southeast Asian pig populations. The findings emphasize the need for continuous and efficient surveillance efforts, not only to protect animal health and the swine industry but also to prevent potential zoonotic outbreaks that could have far-reaching implications for human health and global economies. The study’s recommendations for innovative surveillance approaches pave the way for more effective management of viral threats in the interconnected world of swine and human populations.

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