Fig. 2.

Contribution of receptor binding preference on virus transmissibility in the ferret model. Virus receptor binding is depicted as maintaining a strong avian binding preference (three α2-3 icons), maintaining an avian binding preference with detectable binding to human receptors (two α2-3 icons, one α2-6 icon), enhanced binding to human receptors while maintaining binding to avian receptors (two α2-6 icons, one α2-3 icon) or strong human binding preference (three α2-6 icons) and is not meant to be quantitative. “DC transmission” indicates one inoculated ferret and one naïve ferret co-housed in the same cage, sharing food, water, and bedding; “RD transmission” indicates one inoculated ferret and one naïve ferret housed in adjacent cages separated by a perforated side-wall (3–5 mm in diameter) allowing air exchange only in the absence of direct or indirect contact