Kinetics and magnitude of viral RNA shedding as indicators for Influenza A virus transmissibility in ferrets

The ferret transmission model is routinely used to evaluate the pandemic potential of newly emerging influenza A viruses. However, concurrent measurement of viral load in the air is typically not a component of such studies. To address this knowledge gap, we measured the levels of virus in ferret nasal washes as well as viral RNA emitted into the air for 14 diverse influenza viruses, encompassing human-, swine-, and avian-origin strains. Here we show that transmissible viruses display robust replication and fast release into the air. In contrast, poorly- and non-transmissible viruses show significantly reduced or delayed replication along with lower detection of airborne viral RNA at early time points post inoculation. These findings indicate that efficient ferret-to-ferret transmission via the air is directly associated with fast emission of virus-laden particles; as such, quantification of viral RNA in the air represents a useful addition to established assessments of new influenza virus strains.