Contact heterogeneity, rather than transmission efficiency, limits the emergence and spread of canine influenza virus.

Host-range shifts in influenza virus are a major risk factor for pandemics. A key question in the study of emerging zoonoses is how the evolution of transmission efficiency interacts with heterogeneity in contact patterns in the new host species, as this intery influences disease dynamics and prospects for control. Here we use a synergistic of models and data part the evolutionary and demographic processes controlling a host-range h(-1) equine H3N8-derived canine influenza virus (CIV). CIV has experienced 15 years of continuous transfer among dogs in the United States, bLit maintain patchy distribution, characterized by sporadic short-lived outbreaks coupled with endemic hotspots in large animal shelte how that CIV has ig reproductive potential in these f (mean Ro = 9) and that these hotspots act as refug from he sparsely connected majority of the dog population. Intriguingly, CIV has volved a transmission efficiency that closely matches the minimum required to persist in these refugia, leaving it poised on the extinction/invasion threshold of the host contact network. Corresponding phylogenetic analyses show strong geographic clustering in three US regions, and that the effective reproductive number of the virus (Re) in the general dog population is close to 1.0. Our results highlight the critical role of host contact structure in CIV dynamics and show how host contact networks could shape the evolution of pathogen transmission efficiency. Importantly, efficient control measures could eradicate the virLis, in turn minimizing the risk of future sustained transmission among companion dogs that could represent a potential new axis to the human interface for influenza.