A curve of thresholds governs plague epizootics in Central Asia

Reijniers, Jonas; Davis, Stephen; Begon, Michael; Heesterbeek, J.A.P.; Ageyev, Vladimir S.; Leirs, Herwig

doi:10.1111/j.1461-0248.2012.01767.x

Cited by 34 publications

(49 citation statements)

References 24 publications

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“…When the gerbil population is rapidly increasing in numbers, the flea population is diluted over a larger number of gerbils, decreasing the flea burden per gerbil. Vice versa, a decreasing gerbil population means that fleas will aggregate on the remaining hosts, thus causing a high flea index, and facilitating the rapid transmission of plague [45].…”

Section: Discussionmentioning

confidence: 99%

The trophic responses of two different rodent–vector–plague systems to climate change

Schmid

et al. 2015

Proc. R. Soc. B.

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Plague, the causative agent of three devastating pandemics in history, is currently a re-emerging disease, probably due to climate change and other anthropogenic changes. Without understanding the response of plague systems to anthropogenic or climate changes in their trophic web, it is unfeasible to effectively predict years with high risks of plague outbreak, hampering our ability for effective prevention and control of the disease. Here, by using surveillance data, we apply structural equation modelling to reveal the drivers of plague prevalence in two very different rodent systems: those of the solitary Daurian ground squirrel and the social Mongolian gerbil. We show that plague prevalence in the Daurian ground squirrel is not detectably related to its trophic web, and that therefore surveillance efforts should focus on detecting plague directly in this ecosystem. On the other hand, plague in the Mongolian gerbil is strongly embedded in a complex, yet understandable trophic web of climate, vegetation, and rodent and flea densities, making the ecosystem suitable for more sophisticated low-cost surveillance practices, such as remote sensing. As for the trophic webs of the two rodent species, we find that increased vegetation is positively associated with higher temperatures and precipitation for both ecosystems. We furthermore find a positive association between vegetation and ground squirrel density, yet a negative association between vegetation and gerbil density. Our study thus shows how past surveillance records can be used to design and improve existing plague prevention and control measures, by tailoring them to individual plague foci. Such measures are indeed highly needed under present conditions with prevailing climate change.

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Section: Discussionmentioning

confidence: 99%

The trophic responses of two different rodent–vector–plague systems to climate change

Schmid

et al. 2015

Proc. R. Soc. B.

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“…Plague prevalence among great gerbils (Rhombomys opimus) in Kazakhstan is strongly positively affected by warmer springs and wetter summers (9), and correlates with the population density of the gerbils and fleas themselves (10). When climatic conditions uniformly affect large geographic areas, they can synchronize gerbil densities at the regional scale (11) in a process known as the Moran effect (12,13).…”

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confidence: 99%

Climate-driven introduction of the Black Death and successive plague reintroductions into Europe

Schmid

Büntgen

Easterday

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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The Black Death, originating in Asia, arrived in the Mediterranean harbors of Europe in 1347 CE, via the land and sea trade routes of the ancient Silk Road system. This epidemic marked the start of the second plague pandemic, which lasted in Europe until the early 19th century. This pandemic is generally understood as the consequence of a singular introduction of Yersinia pestis, after which the disease established itself in European rodents over four centuries. To locate these putative plague reservoirs, we studied the climate fluctuations that preceded regional plague epidemics, based on a dataset of 7,711 georeferenced historical plague outbreaks and 15 annually resolved tree-ring records from Europe and Asia. We provide evidence for repeated climate-driven reintroductions of the bacterium into European harbors from reservoirs in Asia, with a delay of 15 ± 1 y. Our analysis finds no support for the existence of permanent plague reservoirs in medieval Europe.

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“…Currently, no empirical data exist to define a burrow density threshold value. However, models such as the flea-density-threshold model [15] predict occupied burrow density threshold values below which no invasion of plague can occur. However, as the occupancy varies over space and time these modelled values cannot be translated into a single threshold burrow density value.…”

Section: Discussionmentioning

confidence: 99%

“…In Eastern Kazakhstan, the presence of this pathogen has been monitored in great gerbils ( Rhombomys opimus ), social rodents that live in burrows, for decades. It has been found that outbreaks of plague occur only when a host and flea abundance threshold is exceeded [14,15], but the direct influence of the landscape on spatial spread and the dynamics of this disease has not previously been investigated.…”

Section: Introductionmentioning

confidence: 99%

Potential corridors and barriers for plague spread in central Asia

Wilschut

Addink

Heesterbeek

et al. 2013

International Journal of Health Geographics

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BackgroundPlague (Yersinia pestis infection) is a vector-borne disease which caused millions of human deaths in the Middle Ages. The hosts of plague are mostly rodents, and the disease is spread by the fleas that feed on them. Currently, the disease still circulates amongst sylvatic rodent populations all over the world, including great gerbil (Rhombomys opimus) populations in Central Asia. Great gerbils are social desert rodents that live in family groups in burrows, which are visible on satellite images. In great gerbil populations an abundance threshold exists, above which plague can spread causing epizootics. The spatial distribution of the host species is thought to influence the plague dynamics, such as the direction of plague spread, however no detailed analysis exists on the possible functional or structural corridors and barriers that are present in this population and landscape. This study aims to fill that gap.MethodsThree 20 by 20 km areas with known great gerbil burrow distributions were used to analyse the spatial distribution of the burrows. Object-based image analysis was used to map the landscape at several scales, and was linked to the burrow maps. A novel object-based method was developed – the mean neighbour absolute burrow density difference (MNABDD) – to identify the optimal scale and evaluate the efficacy of using landscape objects as opposed to square cells. Multiple regression using raster maps was used to identify the landscape-ecological variables that explain burrow density best. Functional corridors and barriers were mapped using burrow density thresholds. Cumulative resistance of the burrow distribution to potential disease spread was evaluated using cost distance analysis. A 46-year plague surveillance dataset was used to evaluate whether plague spread was radially symmetric.ResultsThe burrow distribution was found to be non-random and negatively correlated with Greenness, especially in the floodplain areas. Corridors and barriers showed a mostly NWSE alignment, suggesting easier spreading along this axis. This was confirmed by the analysis of the plague data.ConclusionsPlague spread had a predominantly NWSE direction, which is likely due to the NWSE alignment of corridors and barriers in the burrow distribution and the landscape. This finding may improve predictions of plague in the future and emphasizes the importance of including landscape analysis in wildlife disease studies.

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A curve of thresholds governs plague epizootics in Central Asia

Cited by 34 publications

References 24 publications

The trophic responses of two different rodent–vector–plague systems to climate change

The trophic responses of two different rodent–vector–plague systems to climate change

Climate-driven introduction of the Black Death and successive plague reintroductions into Europe

Potential corridors and barriers for plague spread in central Asia

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