Highly pathogenic avian influenza (HPAI) H5N1 is expanding across species at an unprecedented rate, with recent detections in wild birds, poultry, dairy cattle, and even pigs in the United States. This cross-species adaptability raises urgent concerns for animal health, food security, and global pandemic preparedness. A new scientific review published in Frontiers in Veterinary Science by researchers from the University of Minnesota and CEU Universities in Spain examines the risks of H5N1 in pigs, warning that the swine industry and public health systems must prepare for potential spillovers.
The review, commissioned by the Swine Health Information Center (SHIC), highlights critical knowledge gaps in understanding how H5N1 behaves in pigs, and outlines why pigs—long recognized as “mixing vessels” for influenza—could play a pivotal role in shaping the trajectory of the current outbreak.
Key Findings: Pigs as a Critical “Mixing Vessel”
- Susceptibility confirmed: Experimental infections show that pigs can be infected with bovine- and mink-derived H5N1 strains. While most infections are subclinical and show limited pig-to-pig transmission, viral replication and occasional shedding were observed.
- Potential for viral adaptation: Some H5N1-infected pigs developed mutations linked to mammalian adaptation and antiviral resistance, raising concerns about future virus evolution.
- Field evidence of spillover: In 2024, H5N1 was detected in outdoor pigs in Oregon. Globally, serological evidence from Asia, Europe, and Africa indicates that pigs have repeatedly been exposed to avian influenza viruses in mixed farming systems.
Implications for Public Health and National Security
Pigs have long been recognized as “mixing vessels” for influenza, capable of being co-infected with avian and human-origin viruses. This creates opportunities for genetic reassortment, potentially generating novel strains with pandemic potential. The 2009 H1N1 pandemic, which originated from swine, serves as a reminder of these risks.
For the general public, the issue is not confined to farms or veterinary circles: spillover into pigs could directly impact human health security and national interests. Beyond the risks of human infections, outbreaks threaten food supply chains, economic stability in livestock industries, and the resilience of agricultural systems. Ensuring preparedness in this sector is therefore as much about protecting national security as it is about safeguarding animal health.
Surveillance and Preparedness Challenges
The study emphasizes gaps in diagnostics, noting that standard swine influenza assays may not reliably detect H5N1. Tailored testing and broader surveillance are urgently needed, especially in high-risk interfaces such as mixed livestock systems, outdoor pig populations, and areas with significant wild bird contact.
Biosecurity practices—including water monitoring, control of animal movements, and reduction of contact between domestic and feral swine—are highlighted as essential. Vaccination, while a cornerstone of influenza control in pigs, may need to be rethought due to the antigenic differences between endemic swine influenza viruses and H5N1.
A Call for a One Health Approach
The authors stress that addressing H5N1 in swine requires coordinated action across veterinary, human health, and environmental sectors. The One Health framework is vital to understanding transmission dynamics, guiding vaccine research, and preventing new viral recombinants with pandemic potential.
As the virus continues to expand its host range, the paper concludes, a proactive, science-based response is the only way to stay ahead of a pathogen that has repeatedly proven its ability to surprise us.
Mena-Vasquez J, Marco-Fuertes A, Culhane M, Torremorell M. Emerging threats of HPAI H5N1 clade 2.3.4.4b in swine: knowledge gaps and the imperative for a One Health approach. Frontiers in Veterinary Science, 12 August 2025.