Spatial and Temporal Patterns of Anthrax in White-Tailed Deer, Odocoileus virginianus, and Hematophagous Flies in West Texas during the Summertime Anthrax Risk Period

Abstract

White-tailed deer, Odocoileus virginianus, anthrax epizootics have been frequently documented in Texas over the last two decades. Once outbreaks begin, there is evidence for the potential role of hematophagous flies as vectors for the disease. Hypotheses on the role of biting flies in the transmission of anthrax date back more than a century. Both laboratory experiments and field studies have provided evidence of a biting fly transmission pathway. In particular, several studies have implicated biting flies during severe wildlife outbreaks in North America. Despite these implications, there is a lack of spatial analysis relating flies and anthrax. Here we report on the spatial patterns of anthrax in white-tailed deer on a well-studied ranch with a documented anthrax history. These patterns were evaluated against the spatiotemporal patterns of biting flies during the anthrax risk period. Unbaited fly traps were used to collect flies across the study ranch from June through August 2005. Kernel density analysis confirmed biting fly hotspots concentrated in the areas with highest densities of deer carcasses. The average nearest neighbor index confirmed that deer carcasses were spatially clustered and density estimates suggest that these are in proximity to areas supporting high fly populations. Dual kernel density analysis of carcasses and deer population identified a large dry riverine habitat as a high anthrax risk. Fly catch rates across the period identified a similar pattern to the anthrax risk surface. The high overlap between areas of sustained high fly catch rates and anthrax cases does suggest a relationship warranting future research.