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. 2020 Apr 10;10(1):6186.
doi: 10.1038/s41598-020-63211-4.

Soil salinity and aridity specify plague foci in the United States of America

Rémi Barbieri  1   2 , Gaëtan Texier  3   4 , Catherine Keller  5 , Michel Drancourt  6
Affiliations

Soil salinity and aridity specify plague foci in the United States of America

Rémi Barbieri et al. Sci Rep. .

Abstract

Plague is a deadly zoonosis that periodically reemerges as small outbreaks in geographically limited foci where the causative agent Yersinia pestis may reside in soil. We analyzed a dataset of 1.005 carefully documented plague cases that were georeferenced over 113 years in peer-reviewed literature in the contiguous United States. Plotting outbreaks by counties defined as plague foci on geographical maps, we observed a significant co-localization of plague outbreaks with high soil salinity measured by an electric conductivity of >4 dS/ m-1 and aridity measured by an aridity index <0.5. Thus, we identified aridity and soil salinity as significantly associated with ecological risk factors for relapsing plague in the contiguous United States. These results reveal two evolutive parameters that are partially associated with anthropic activities, complicating the epidemiology of plague in the contiguous United States. Exploiting aridity and soil salinity data may help in the surveillance of evolving plague foci in the contiguous United States.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Dynamic of plague in the USA, 1900 to 2012: The map features the appearance of the very first case per county, corresponding to 136 counties. Color code corresponds to the chronology.
Figure 2
Figure 2
Choropleth map of the 57 plague foci featuring cumulative incidence per 100,000 inhabitants per county in the USA, 1910–2012.
Figure 3
Figure 3
Heatmap of yearly plague incidence in 57 plague foci (x axis) classified from western counties to eastern counties (y axis) in the USA, 1910–2012.
Figure 4
Figure 4
Cumulative map featuring aridity, salinity and the 57 plague foci per county in the USA.
Figure 5
Figure 5
Fisher’s exact testing the association of plague in the 57 plague foci versus salinity (a), aridity (b) and salinity versus aridity (c) in the USA.
Figure 6
Figure 6
Ecological studies of cumulative plague incidence per 100,000 inhabitants in the 57 plague foci versus aridity (a) (expressed as mean Aridity Index by county (see material and methods)), and salinity (b) (expressed as mean Salinity index by county (see material and methods)) per county in the USA. The dotted black lines represent fitted Loess regressions. On the right of each scatterplots, the percentage of counties in which plague cases were documented is reported using barplots.
See this image and copyright information in PMC

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