Mechanisms Underlying the Airborne Transmission of Seasonal Influenza A Viruses

Mechanisms Underlying the Airborne Transmission of Seasonal Influenza A Viruses PROJECT SUMMARY Seasonal influenza A viruses, particularly the H1N1 and H3N2 subtypes, continue to pose major public health threats, causing substantial morbidity and mortality worldwide each year. Although these subtypes differ significantly in clinical severity, age distribution, and geographic circulation, the mechanisms by which viral subtype and environmental factors interact to influence airborne transmission remain poorly understood. To date, no systematic studies have determined whether H1N1 and H3N2 differ in aerosol particle size distributions, virion morphology, or environmental stability in ways that impact airborne spread. The overall objective of this project is to investigate the mechanisms that shape airborne transmission of influenza A viruses and to determine how viral subtype influences the effect of environmental conditions, specifically temperature and relative humidity, on transmission. We hypothesize that differences in virion morphology, aerosol particle characteristics, and environmental stability contribute to subtype-specific transmission potential. To test this hypothesis, three complementary aims are proposed. In Aim 1, we will characterize the aerosol particle size distributions and virion morphologies of H1N1 and H3N2 viruses using samples from human patients, laboratory-generated aerosols, and experimentally infected swine, applying our novel PathoSift Pro aerosol sampler and imaging techniques, including transmission electron microscopy and advanced cryo-electron tomography. In Aim 2, we will systematically evaluate how temperature and relative humidity affect viral viability and particle transport in fluids derived from tracheal and lung washes of infected pigs, using a custom-engineered aerosol exposure system. These data will be integrated into a fate and transport model that combines continuous random walk simulations with computational fluid dynamics to predict transmission risk. In Aim 3, we will assess subtype-specific airborne transmission in a swine model using barcoded viruses under a controlled environmental condition, tracking transmission chains and correlating particle exposure with infection outcomes. Computational fluid dynamics modeling will be combined with exposure and infection data to define how aerosol particle dynamics and environmental parameters jointly influence transmission efficiency. This study will generate foundational knowledge to define how viral and environmental factors jointly influence airborne transmission for influenza viruses. The results will directly inform public health preparedness by improving predictive models and guiding evidence-based interventions for mitigating seasonal and pandemic influenza, and as well as other airborne pathogens.