Spatial Aspects of Epidemic I Pathogen Dispersal and Disease Gradients

Disease spread is the result of inoculum dispersal. Dispersal is the movement of infectious units (e.g., spores) of a pathogen from one place to another or the movement of infectious units from the place they were formed to other locations. We consider the terms propagules, propagative units, and units of inoculum as being equivalent to infectious units in this chapter. Because propagative units mostly move short distances, new infections primarily occur near other infections and, therefore, there usually is higher disease intensity in some locations than others. If the inoculum initially is concentrated in one location, one can study dispersal by measuring the spore deposition on surfaces (e.g., leaves, flowers) at a range of distances from the inoculum source. Likewise, if diseased individuals are initially concentrated in a focus in one area, disease spread can be determined by measuring disease intensity at a range of distances from the initial disease source. However, if there are many inoculum sources, or diseased individuals are located at multiple locations at the start of an epidemic, then disease spread may not be easily measured (although the same biological process is occurring). This is because it will not be known where a deposited spore originated or which inoculum source produced the spore that resulted in a new diseased individual at a given location. Chapter topics include: Introduction Dispersal Gradients, Disease Gradients, and Disease Spread Models Model Fitting Disease Gradients—Correcting for Maximum Intensity Spatio-Temporal Dynamics of Disease Spread Disease Management