Baseline Review of the Upper Tana, Kenya

http://greenwatercredits.net/sites/default/files/documents/isric_gwc_report8.pd

Remote sensing for landscape epidemiology : spatial analysis of plague hosts in Kazakhstan

The spatial distribution of hosts is a crucial aspect for the understanding of infectious disease dynamics. In Kazakhstan, the great gerbil (Rhombomys opimus) is the main host for plague (Yersinia pestis infection) and poses a public health threat, yet their spatial distribution is unknown. Great gerbils are social animals that live in family groups in burrows in desert environments. Plague is transmitted from gerbil to gerbil via fleas, and can also be transmitted to humans. In Kazakhstan, an abundance threshold exists above which plague can spread over larger areas. This means that the great gerbils’ distribution is crucial to the spread and persistence of this disease. To gain information on the spatial distribution of the great gerbils, the spatial distribution of their burrows needs to be known. High-resolution satellite images were used in combination with a classification technique called Random Forests to identify the burrows of the great gerbils, which resulted in overall accuracies ranging from 87 to 97%. Once the burrow distribution was known, the relation between the abundance of great gerbil burrows and the landscape was studied. Multiple regression showed that burrow density was negatively related to Greenness, especially in the floodplain areas. 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 existed on the possible corridors and barriers that were present. Corridors and barriers were mapped using a burrow density threshold, and were mostly aligned on the NWSE axis. To investigate whether plague spread was radially symmetric in the past, a plague presence and absence data set was used. Results showed that plague spread had occurred mostly along the NWSE axis. This associates great-gerbil-burrow density with the direction of plague spread. In plague-prediction models, great-gerbil burrows are assumed to be randomly or regularly distributed. However, this assumption has never been validated. Spatial point-pattern statistics were used on field data to see whether the occupied burrows are clustered within the total population of burrows. The results showed that burrows irrespective of occupancy were regularly distributed. It also showed that occupied burrows are clustered, but that this can only be detected in squares of 500 m and larger. To be able to predict plague outbreaks in Kazakhstan effectively, the real-time distribution of occupied burrows needs to be known, preferably for large areas. An NDVI time-series was used to identify occupied burrows, and classify them from space. Classification accuracies are promising with an overall accuracy of 65%. It is concluded that great gerbil burrows irrespective of occupancy are spatially structured and related to the landscape at larger scales, and that they are regularly distributed at local scales. Occupied burrows are spatially clustered. This should be incorporated into plague models. Furthermore, with the newly developed method, occupied burrows can now be detected from space. This will aid the prediction of plague outbreaks. Together, these findings allow for more realistic approaches to disease ecology models for both this system and for other structured host populations

Stad kleurt rood op de hittekaart: Onderzoek van HvA toont nut en mogelijkheden van hittekaarten voor toekomstige inrichting van steden

Het bestuur van gemeenten en steden staat voor de grote opgave de stad tijdens hete zomers prettig en leefbaar te maken. Hittekaarten vormen daarbij een handig hulpmiddel en geven aan waar het in de stad heet is en waar het juist koel blijft. Daarmee maken de kaarten inzichtelijk waar hittemaatregelen precies effect hebben. Wat hittekaarten kunnen betekenen voor stadsbestuur was één van de drie kernvragen in het onderzoeksproject Hittebestendige stad van de Hogeschool van Amsterdam (HvA)

Local persistence and extinction of plague in a metapopulation of great gerbil burrows, Kazakhstan

Speculation on how the bacterium Yersinia pestis re-emerges after years of absence in the Prebalkhash region in Kazakhstan has been ongoing for half a century, but the mechanism is still unclear. One of the theories is that plague persists in its reservoir host (the great gerbil) in so-called hotspots, i.e. small regions in which the conditions remain favourable for plague to persist during times where the conditions in the Prebalkhash region as a whole have become unfavourable for plague persistence. In this paper we use a metapopulation model that describes the dynamics of the great gerbil. With this model we study the minimum size of an individual hotspot and the combined size of multiple hotspots in the Prebalkhash region that would be required for Y. pestis to persist through an inter-epizootic period. We show that the combined area of hotspots required for plague persistence is so large that it would be unlikely to have been missed by existing plague surveillance. This suggests that persistence of plague in that region cannot solely be explained by the existence of hotspots, and therefore other hypotheses, such as survival in multiple host species, and persistence in fleas or in the soil should be considered as well

Local persistence and extinction of plague in a metapopulation of great gerbil burrows, Kazakhstan

Speculation on how the bacterium Yersinia pestis re-emerges after years of absence in the Prebalkhash region in Kazakhstan has been ongoing for half a century, but the mechanism is still unclear. One of the theories is that plague persists in its reservoir host (the great gerbil) in so-called hotspots, i.e. small regions in which the conditions remain favourable for plague to persist during times where the conditions in the Prebalkhash region as a whole have become unfavourable for plague persistence. In this paper we use a metapopulation model that describes the dynamics of the great gerbil. With this model we study the minimum size of an individual hotspot and the combined size of multiple hotspots in the Prebalkhash region that would be required for Y. pestis to persist through an inter-epizootic period. We show that the combined area of hotspots required for plague persistence is so large that it would be unlikely to have been missed by existing plague surveillance. This suggests that persistence of plague in that region cannot solely be explained by the existence of hotspots, and therefore other hypotheses, such as survival in multiple host species, and persistence in fleas or in the soil should be considered as well

Local persistence and extinction of plague in a metapopulation of great gerbil burrows, Kazakhstan

Speculation on how the bacterium Yersinia pestis re-emerges after years of absence in the Prebalkhash region in Kazakhstan has been ongoing for half a century, but the mechanism is still unclear. One of the theories is that plague persists in its reservoir host (the great gerbil) in so-called hotspots, i.e. small regions in which the conditions remain favourable for plague to persist during times where the conditions in the Prebalkhash region as a whole have become unfavourable for plague persistence. In this paper we use a metapopulation model that describes the dynamics of the great gerbil. With this model we study the minimum size of an individual hotspot and the combined size of multiple hotspots in the Prebalkhash region that would be required for Y. pestis to persist through an inter-epizootic period. We show that the combined area of hotspots required for plague persistence is so large that it would be unlikely to have been missed by existing plague surveillance. This suggests that persistence of plague in that region cannot solely be explained by the existence of hotspots, and therefore other hypotheses, such as survival in multiple host species, and persistence in fleas or in the soil should be considered as well