Abstract
BackgroundAnthrax, a soil-borne zoonosis caused by the bacterium Bacillus anthracis, is enzootic in areas of North America with frequent outbreaks in west Texas. Despite a long history of study, pathogen transmission during natural outbreaks remains poorly understood. Here we combined case-level spatio-temporal analysis and high resolution genotyping to investigate anthrax transmission dynamics. Carcass locations from a single white-tailed deer, Odocoileus virginanus, outbreak were analyzed for spatial clustering using K-function analysis and directionality with trend surface analysis and the direction test.ResultsThe directionalities were compared to results of high resolution genotyping. The results of the spatial clustering analyses, combined with deer movement data, suggest anthrax transmission events occur within limited spatial areas, with carcass locations occurring within the activity space of adjacent cases. The directionality of the outbreak paralleled adjacent dry river beds. Isolates from the outbreak were represented by a single genotype based on multiple locus variable number tandem repeat analysis (MLVA); four sub-genotypes were identified using single nucleotide repeat (SNR) analysis.ConclusionsAreas of high transmission agreed spatially with areas of higher SNR genetic diversity; however, SNRs did not provide clear evidence of linear transmission. Overlap of case home ranges provides spatial and temporal support for localized transmission, which may include the role of necrophagous or hematophagous flies in outbreaks in this region. These results emphasize the need for active surveillance and prompt cleanup of anthrax carcasses to control anthrax both during outbreaks and between seasons.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-015-0054-8) contains supplementary material, which is available to authorized users.
Highlights
Anthrax, a soil-borne zoonosis caused by the bacterium Bacillus anthracis, is enzootic in areas of North America with frequent outbreaks in west Texas
Bacillus anthracis was cultured from 16 of 17 carcasses from which samples were obtained A presumptive B. anthracis isolate was recovered from the additional carcass, but failed to genotype as B. anthracis using multiple locus variable number tandem repeat analysis (MLVA)-25 typing
Among white-tailed deer in West Texas, anthrax transmission events occurred within limited spatial areas and carcass locations were within activity spaces of subsequent cases, indicating interaction of animals with carcass sites during outbreaks is essential to anthrax outbreak dynamics in this landscape
Summary
A soil-borne zoonosis caused by the bacterium Bacillus anthracis, is enzootic in areas of North America with frequent outbreaks in west Texas. Because outbreaks are spatially localized and temporally limited across most ecosystems [9, 15], micro and meso scale ecological processes, driven by local climate, host and vector species, and host behavior, are important, but poorly studied, determinants of anthrax ecology. Characterizing these processes informs prevention and control efforts, the latter of which rely on prompt identification and disposal of carcasses [18]
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