Figure 1.

Illustration and definition of the concept of pathogen spreadability, a trait relevant for a range of directly transmitted pathogens. For context, we also define three epidemiological traits that are most related yet still distinct from spreadability, and note their expected relationship with spreadability. For most systems, pathogen spreadability would need to be combined with related traits such as pathogen load to generate robust overall estimates for a given strain's ‘force of infection’, defined generally as a product of the contact rate between susceptible and infectious hosts, and the probability that a given contact results in successful transmission [15]. While spreadability influences both components of the force of infection, the average pathogen load available for spread will also contribute to the latter component. Figure made in Biorender.