A novel type of self-avoiding walk revealed by Influenza A’s motion on coverslips

The locomotion of virions has been a nonsubject---it was always assumed that the motion of virus particles in the extracellular space is governed by Brownian motion. However, traversing the dense mucus layer, particularly during attempts by the host to clear it, presents a formidable challenge. An estimate of the probability p that a virion overcomes the mucosal barrier, assuming simple diffusion, gives $p<10^-3$. Hence, passive diffusion alone would render a virus incapable of infection. In 2019, it was discovered that Influenza A viruses (IAVs) exhibit a striking departure from random diffusion, displaying remarkable persistence and direction in their motion on functionalized coverslips through a spatial segregation of binding and enzymatic cleaving activity on their viral envelope. In this talk, we show that a mean-squared displacement analysis of IAV trajectories unveils a distinct superdiffusive, self-avoiding walk (SAW) pattern. We present a model that elucidates the underlying ‘burnt-bridge’ Brownian ratchet mechanism, effectively transforming stochastic binding, unbinding, and cleaving events into directed motion. The model allows for a quantitative comparison with the experiments and explains the observed SAW characteristics of IAV trajectories. Furthermore, our model provides novel insights into strategies to hinder viral motility, potentially opening avenues for antiviral therapeutic intervention.