Findings Published from H5N1 Swine Risk Project Funded by SHIC, FFAR, and Pork Checkoff

The Swine Health Information Center, in collaboration with the Foundation for Food & Agriculture Research and the Pork Checkoff, funded 10 projects addressing research priorities and topics within its H5N1 Risk to Swine Research Program in July 2025. One project led by Dr. Yan Zhou, Vaccine and Infectious Disease Organization (VIDO), University of Saskatchewan, has recently published results in the Journal of Virology entitled “Receptor profiling and growth assessment of influenza A virus in porcine mammary and non-mammary tissues and derived cells.” Researchers said their findings suggest porcine mammary gland could support infection with HPAI 2.3.4.4b genotype B3.13.

The goals of the SHIC/FFAR/NPB H5N1 Risk to Swine Research Program are to enhance prevention, preparedness, mitigation, and response capabilities for H5N1 influenza in the US swine herd. Given the recent evidence of H5N1 replication in bovine mammary gland, it is important to address the question whether the porcine mammary gland could similarly support influenza virus infection. This study was intended to provide insights into whether porcine mammary tissue could serve as a site for virus replication as well as assess the potential for bovine H5N1 to replicate in the porcine respiratory tract compared to other IAV strains.

The project sought to characterize the sialic acid (SA) receptors present in the porcine mammary gland and respiratory tract tissues, including nasal turbinate, trachea, bronchiole, and alveoli, and assess the ability for IAV to bind to these tissues. Researchers identified that porcine mammary gland tissue, nasal turbinate, bronchiole, and alveoli express both SA-α2,3 and SA-α2,6 receptors, suggesting that these tissues may be susceptible to attachment by both avian and mammalian origin IAVs.

In addition, the study found that influenza viruses originating from cattle, birds, swine, and humans could bind to porcine respiratory and mammary gland tissues, although binding intensity varied by virus and tissue type. Primary epithelial cells isolated from these tissues also supported viral replication, with bovine-derived H5N1 showing particularly strong replication in mammary gland cells. These results suggest that receptor availability alone does not determine whether the H5N1 virus can replicate efficiently, with additional host and viral factors also playing critical roles.

Importantly, the study demonstrated that porcine mammary epithelial cells possess the ability to support replication of diverse IAV strains, raising the possibility that the mammary gland could serve as an alternative site for viral replication and potential reassortment. However, the authors emphasize that these laboratory findings differ from previous animal studies, where H5N1 infection in pigs has generally resulted in limited viral replication, mild clinical signs, and little to no transmission. The discrepancy highlights the influence of natural protective barriers—including mucus, tissue architecture, immune responses, and overall viral fitness—that cannot be fully replicated in cell culture systems.

In the published report, authors wrote, “Our findings expand the current understanding of IAV (influenza A virus) tissue tropism in swine by revealing that the porcine mammary gland may serve as an alternative and previously overlooked replication site for both avian and mammalian-origin viruses. Given the increasing frequency of interspecies spillover events and expanding host range of HPAI H5N1, our finding that mammary epithelial cells have an intrinsic capacity to support replication of diverse IAV strains provides new insight into the porcine mammary gland as a potential replication and reassortment site for IAV.”

While the findings were generated using laboratory cell and tissue models—not live pigs—they highlight an area that warrants further investigation. Additional swine studies are needed and currently underway to determine whether the mammary gland becomes infected during natural or experimental H5N1 exposure and what role, if any, it plays in disease transmission or virus evolution.

Why This Matters for Pork Producers

Although this study does not indicate that H5N1 is currently present within swine populations, it provides important new information about how emerging influenza viruses may interact with pigs. As H5N1 continues to infect an expanding range of animal species, understanding all potential sites of viral replication is critical for surveillance, risk assessment, and preparedness.

For pork producers and veterinarians, the findings reinforce the importance of:

• Maintaining strong biosecurity to reduce opportunities for influenza viruses to move between species.
• Monitoring emerging influenza viruses as part of herd health surveillance.
• Recognizing that influenza viruses may have biological capabilities not previously appreciated, even if those capabilities do not necessarily translate into disease under field conditions.
• Supporting continued research is required to better understand the risks posed by evolving H5N1 viruses to swine health, production, and the pork industry.
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Overall, the study provides new insight into influenza biology while underscoring that additional research is needed to help inform potential changes to IAV surveillance and swine health management recommendations. Outcomes from the funded projects such as this provide critical and proactive information that producers, veterinarians, and industry stakeholders can use to better prevent incursion and develop preparedness plans if H5N1 is ever identified in US commercial swine herds.

Reference: Barron-Castillo U, Berube N, Swan CL, Javed MA, Aubrey L, Trann J, Gidych M, Shrivastava S, Baid K, Banerjee A, Zhou Y.0. Receptor profiling and growth assessment of influenza A virus in porcine mammary and non-mammary tissues and derived cells. J Virol 0:e00615-26. https://doi.org/10.1128/jvi.00615-26

Foundation for Food & Agriculture Research

The Foundation for Food & Agriculture Research (FFAR) builds public-private partnerships to fund bold research addressing big food and agriculture challenges. FFAR was established in the 2014 Farm Bill to increase public agriculture research investments, fill knowledge gaps and complement the U.S. Department Agriculture’s research agenda. FFAR’s model matches federal funding from Congress with private funding, delivering a powerful return on taxpayer investment. Through collaboration and partnerships, FFAR advances actionable science benefiting farmers, consumers and the environment.

Swine Health Information Center

The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Megan Niederwerder at [email protected] or Dr. Lisa Becton at [email protected].