In a recent study published in Nature Communications, researchers have identified a novel influenza strain, α-swH1N2, which exhibits increased pandemic potential. This strain has raised concerns among public health experts due to its ability to potentially spread rapidly across populations.
The current study focuses on evaluating the pandemic potential of two influenza A virus clades, α-H1 and γ-H1, chosen for their geographical spread, detection frequency, interspecies transmission from pigs to ferrets, documented human variants, and reduced cross-reactivity with seasonal human vaccines. Researchers developed a decision tree to characterize and assess the pandemic risk posed by endemic swine influenza A viruses (IAVs), integrating extensive research conducted since the 2009 H1N1 pandemic using both in vitro and in vivo methods.
Influenza A viruses (IAVs) are a significant public health concern due to their genetic diversity and limited immunity in the population. These viruses, known as flu, infect millions annually and can lead to occasional pandemics in humans. Swine IAVs specifically affect pigs, causing respiratory symptoms like coughing, breathing difficulties, nasal discharge, sneezing, fever, and sometimes pneumonia. IAVs pose a significant public health threat due to their genetic diversity and the limited immunity they generate in the population. These viruses, commonly known as flu, infect millions annually and can occasionally lead to pandemics in humans. Swine IAVs specifically affect pigs, causing respiratory symptoms such as coughing, breathing difficulties, nasal discharge, sneezing, fever, and sometimes pneumonia.
Previous studies by Senthilkumar and colleagues investigated H1N1 infections in Indian pigs from 2009 to 2016 using the HI assay. They found varying seroprevalence rates, ranging from 5.2% in 2009 to 36.3% in 2011, with Eastern Uttar Pradesh recording antibody rates between 6.2% and 37.5%. These findings suggest concurrent circulation of seasonal and pandemic H1N1 viruses, highlighting potential cross-species influenza transmission.
Previous research has indicated significant antigenic differences in α-swH1N2 viruses compared to human vaccine strains, affecting transmission rates to ferrets and recognition by human antibodies. This lack of cross-neutralizing antibodies in human sera from ferrets immunized with H1N1pdm09 or H3N2 suggests that prior seasonal virus infections do not confer immunity against α-swH1N2.
The study also found varied levels of anti-N2 antibodies across different birth cohorts, indicating variable NA-based immunity, particularly in specific populations. α-swH1N2 demonstrated efficient airborne transmission to ferrets regardless of their immune status, with previously exposed animals showing milder symptoms, reminiscent of observations during the 2009 pandemic where reduced severity and mortality were noted.
In immune hosts lacking neutralizing antibodies, CD8+ T-cells recognize conserved internal viral proteins, aiding recovery and virus clearance across influenza subtypes. However, immunity from human seasonal viruses did not prevent airborne α-swH1N2 infection. Ferrets previously infected with H1N1pdm09 cleared α-swH1N2 more quickly, reducing shedding duration and symptom severity.
Despite reduced severity in immune hosts, H1N1pdm09 maintained a 50% transmission efficiency, indicating silent spread and potential pandemic risk. Enhanced surveillance and prompt detection of zoonotic outbreaks, along with targeted vaccination campaigns against the α-H1 clade in swine, are critical to mitigating viral spread.
Reference
- Potential pandemic risk of circulating swine H1N2 influenza viruses | Nature Communications [Internet]. [cited 2024 Jun 24]. Available from: https://www.nature.com/articles/s41467-024-49117-z
- The global antigenic diversity of swine influenza A viruses | eLife [Internet]. [cited 2024 Jun 24]. Available from: https://elifesciences.org/articles/12217#abstract
- Lewis NS, Russell CA, Langat P, Anderson TK, Berger K, Bielejec F, et al. The global antigenic diversity of swine influenza A viruses. eLife. 5: e12217.
- Senthilkumar D, Kulkarni DD, Venkatesh G, Gupta V, Patel P, Dixit M, et al. Widespread Prevalence of Antibodies Against Swine Influenza A (pdm H1N1 09) Virus in Pigs of Eastern Uttar Pradesh, India. Curr Microbiol. 2021;78(7):2753–61.
- Li Y, Robertson I. The epidemiology of swine influenza. Anim Dis. 2021;1(1):21.