Is H5N1 a threat to U.S. swine herds?

The Swine Health Information Center, in collaboration with the American Association of Swine Veterinarians, recently hosted a webinar on influenza A viruses, with the goal being to understand the threat highly pathogenic avian influenza H5N1 poses to domestic livestock species and to inform producers of actions that can be taken to prevent infection on-farm.

Amy Baker, research veterinary medical officer at the USDA National Animal Disease Center, kicked off the discussion wiht an overview of influenza A virus in swine. Influenza A has a negative strand RNA genome, is enveloped and contains two major surface glycoproteins – hemagglutinin and neuraminidase. Influenza A is prone to rapid evolution by two main processes – genetic mutation and reassortment – and that the virus escapes population immunity by antigenic drift and/or shift. With reassortment, influenza A evolution can lead to antigenic shift which was seen in the 2009 H1N1 pandemic in humans.

Baker noted influenza is constantly changing and shared that wild waterfowl are a native host for the virus. Influenza from waterfowl has the potential to infect swine and those same viruses can also interact with humans and poultry. During her presentation, Baker highlighted how several species, including pigs, birds, wild mammals and humans, have the potential to serve as mixing vessels and share the influenza A virus among mammalian species.

She also reviewed the ongoing USDA IAV surveillance in swine, noting the system has been active since 2009. Viruses identified at veterinary diagnostic laboratories are initially screened for the presence of IAV through PCR. The current testing methodology can detect the different H and N glycoproteins including H5N1. Cases that meet specific criteria can then be added into the surveillance for further whole genome sequences.

Three sample streams are incorporated into the current surveillance system, including:

1.Case-compatible swine accessions to the NAHLN laboratories

2.Swine population samples epidemiologically linked to a human case of IAV

3.Swine exhibiting influenza-like illness at commingling events such as fairs or exhibition events

Goals of the surveillance system are to monitor the genetic evolution of endemic IAV in swine and make influenza isolates from swine available for research. Further, goals include establishing a data management system for genetic analysis to facilitate the development of relevant diagnostic reagents, updating diagnostic assays, and identifying proper isolates for vaccine seed stock.

The ongoing surveillance system helps to address the human/swine influenza A interface. Baker noted that human influenza A greatly influences the pathogen’s diversity in swine due to interspecies transmission from humans to swine. Surveillance of influenza viruses assists with the One Health approach to understand swine influenza A hemagglutinin and neuramidase diversity in the U.S. and globally. Human variant cases from swine hemagglutinin clades are detected globally and monitored by the World Health Organization Collaborating Centres of the Global Influenza Surveillance and Response System. The USDA Swine Surveillance system provides valuable information regarding the evolution of the virus within the U.S. to benefit swine and human populations. Baker highlights the public health-animal health collaboration within the influenza community as a success story. While the current HPAI H5N1 panzootic is a concern for swine health and human pandemic preparedness, robust surveillance and disease investigation are the foundation for improving intervention strategies for animal and public health, Baker concluded.