Evaluating the spatial ecology of anthrax in North America: Examining epidemiological components across multiple geographic scales using a GIS-based approach.

摘要

This dissertation explores the spatial ecology and potential pathways of infection of anthrax, Bacillus anthracis, in North America. A multi-scale approach was used to evaluate the components required for disease agent survival in the environment, interactions with wildlife, and the potential role that vectors play in anthrax transmission. First, ecological niche modeling with the Genetic Algorithm for Rule-set Production (GARP) was used to predict the geographic distribution of anthrax in the continental U.S. using case data from outbreaks between 1957 and 2005. These results were then used to produce the first quantitative, continental scale predictions of anthrax in Mexico. At the meso-scale, the route of transmission in white-tailed deer is unknown, despite a large number of outbreaks in wild deer in Texas in recent years (2001--2005). To determine the interactions between deer and potential anthrax sources, two pilot studies were conducted on (1) the distribution of biting flies in relation to anthrax cases to evaluate the potential role of hematophagous flies as vectors, and (2) the summer home ranges of deer in relation to fly densities and carcass locations. The results of the GARP studies support the use of the technique for modeling the niche of this disease and suggest a central corridor of anthrax habitat from southwest Texas to the Canadian border, with disjunct areas in the Pacific Northwest and California. Mexico's predicted areas were extensions of the Texas and California ranges. The deer study suggests that deer interactions with spores occur within a limited home range in Texas and long-distance movement of spores is unlikely by individual deer. Biting fly densities were highest in areas of known anthrax infection and lowest in areas where case-positive deer have not been identified, suggesting that flies may play a role in disease transmission, either through mechanical transmission or through increased nuisance that leads to immuno-suppression in deer. This dissertation presents the first continental-scale predictions for the geographic distribution of anthrax in the U.S. and Mexico. Additionally, this is the first known study to evaluate spatial patterns between known cases, fly densities, and animal movements.