Management matters when fighting IAV
Influenza A virus continues to challenge pork production. It mutates. It reassorts. It exploits management gaps and thrives on opportunity. New field data now show that everyday barn level decisions directly influence how genetically diverse and complex this virus becomes inside a herd.
The data cited here is from a presentation by Joaquin Alvarez-Norambuena, a veterinary science graduate student, and colleagues at the University of Minnesota during the Leman Swine Conference in 2025. Their research examined how herd management practices shape the genetic diversity of influenza A virus (IAV) in weaning piglets.
Influenza A is built for change. Its segmented genome allows gene segments to reshuffle when multiple strains infect the same pig. Distinct strains often circulate simultaneously. New strains, including those of human origin, are regularly introduced. The result is constant viral evolution and the ongoing risk of new reassortment viruses emerging in commercial herds.
Researchers used whole genome sequencing on IAV-positive nasal swabs collected from weaning piglets on 14 farms. Each gene segment was classified by lineage, and a viral genotype was defined by the full combination of those segments. Herd level diversity was also measured, capturing both the number of unique genotypes and how evenly they were distributed.
Differences between farms were clear. Some herds showed high genotype richness and evenness. Others had far lower diversity. Management practices helped explain why.
Vaccination timing emerged as the most influential factor. Herds using mass vaccination or pre-farrow vaccination had significantly lower genotype diversity. Farms that did not vaccinate showed higher diversity. Well-timed vaccination appears to limit co-infection and reduce opportunities for reassortment.
Gilt management also mattered. All-in, all-out gilt flow at the room or barn level was associated with lower viral diversity. Continuous flow systems were linked to higher diversity. Tighter population control reduces mixing and limits strain interaction.
Ventilation played a role. Herds with mechanical ventilation showed lower diversity compared to those using mixed systems. Controlled airflow may reduce viral spread and co-infection pressure.
Gilt sourcing influenced outcomes as well. Farms sourcing gilts internally, from within the same production system, had lower IAV diversity. External gilt sourcing was associated with higher diversity, reinforcing the risk that new introductions bring new strains. (Make sure to quarantine new animals – always.)
Two factors were associated with increased diversity. Recent introduction of porcine reproductive and respiratory syndrome (PRRS) virus correlated with higher IAV diversity, likely due to increased co-infection and viral replication. Larger herd sizes also aligned with greater diversity, reflecting more transmission events and more chances for viral mixing.
The takeaway is direct. Influenza diversity responds to management pressure. Vaccination strategy, gilt flow, ventilation, biosecurity, herd size and control of other diseases all shape how much room the virus has to evolve.
Producers may not eliminate IAV overnight, but disciplined management can narrow the virus’s evolutionary playground and reduce the risk of disruptive new strains emerging.
by Enrico Villamaino
