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United States Department of Agriculture

Agricultural Research Service

Research Project: EVALUATION AND IMPROVEMENT OF CEREAL GERMPLASM FOR DISEASE RESISTANCE AND WINTER-HARDINESS

Location: Plant Science Research

Title: Aerial dispersal and multiple-scale spread of epidemics

Authors
item Mundt, Christopher - OREGON STATE UNIVERSITY
item Sackett, Kathryn - OREGON STATE UNIVERSITY
item Wallace, Larae - OREGON STATE UNIVERSITY
item Cowger, Christina
item Dudley, Joseph - SCI APPLICATION INTL CORP

Submitted to: EcoHealth
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 2009
Publication Date: February 13, 2010
Citation: Mundt, C.C., Sackett, K.E., Wallace, L.D., Cowger, C., Dudley, J.P. 2010. Aerial dispersal and multiple-scale spread of epidemics. EcoHealth. DOI: 10.1007/s10393-009-0251-z.

Interpretive Summary: Disease spread has traditionally been described as a traveling wave of constant velocity. However, aerially dispersed pathogens capable of long distance dispersal (LDD) often have dispersal gradients with extended tails that could result in acceleration of the epidemic front over time and space. We applied empirical data to a simple model of disease spread that incorporates a logistic equation to describe temporal disease increase and an inverse power function for pathogen dispersal. The model suggests that the position of the epidemic front will increase exponentially with time and that epidemic velocity increases linearly with distance. The scale invariance of the power law dispersal function allowed us to apply the model to spatial scales over five orders of magnitude, from experimental field plots to continental-scale epidemics incorporating both plant and animal diseases. It also may be possible to scale epidemics to account for effects of initial focus size and degree of host heterogeneity. The slope of the inverse power law approximated 2 for the data sets investigated, which would suggest that the position of the epidemic front doubles per unit time and that the slope of velocity plotted against distance is approximately 1/2.

Technical Abstract: Disease spread has traditionally been described as a traveling wave of constant velocity. However, aerially dispersed pathogens capable of long distance dispersal (LDD) often have dispersal gradients with extended tails that could result in acceleration of the epidemic front over time and space. We applied empirical data to a simple model of disease spread that incorporates a logistic equation to describe temporal disease increase and an inverse power function for pathogen dispersal. The model suggests that the position of the epidemic front will increase exponentially with time and that epidemic velocity increases linearly with distance. The scale invariance of the power law dispersal function allowed us to apply the model to spatial scales over five orders of magnitude, from experimental field plots to continental-scale epidemics incorporating both plant and animal diseases. It also may be possible to scale epidemics to account for effects of initial focus size and degree of host heterogeneity. The slope of the inverse power law approximated 2 for the data sets investigated, which would suggest that the position of the epidemic front doubles per unit time and that the slope of velocity plotted against distance is approximately 1/2.

Last Modified: 9/23/2014