The Perfect Burrow, but for What? Identifying Local Habitat Conditions Promoting the Presence of the Host and Vector Species in the Kazakh Plague System

Abstract

IntroductionThe wildlife plague system in the Pre-Balkhash desert of Kazakhstan has been a subject of study for many years. Much progress has been made in generating a method of predicting outbreaks of the disease (infection by the gram negative bacterium Yersinia pestis) but existing methods are not yet accurate enough to inform public health planning. The present study aimed to identify characteristics of individual mammalian host (Rhombomys opimus) burrows related to and potentially predictive of the presence of R.opimus and the dominant flea vectors (Xenopsylla spp.).MethodsOver four seasons, burrow characteristics, their current occupancy status, and flea and tick burden of the occupants were recorded in the field. A second data set was generated of long term occupancy trends by recording the occupancy status of specific burrows over multiple occasions. Generalised linear mixed models were constructed to identify potential burrow properties predictive of either occupancy or flea burden.ResultsAt the burrow level, it was identified that a burrow being occupied by Rhombomys, and remaining occupied, were both related to the characteristics of the sediment in which the burrow was constructed. The flea burden of Rhombomys in a burrow was found to be related to the tick burden. Further larger scale properties were also identified as being related to both Rhombomys and flea presence, including latitudinal position and the season.ConclusionsTherefore, in advancing our current predictions of plague in Kazakhstan, we must consider the landscape at this local level to increase our accuracy in predicting the dynamics of gerbil and flea populations. Furthermore this demonstrates that in other zoonotic systems, it may be useful to consider the distribution and location of suitable habitat for both host and vector species at this fine scale to accurately predict future epizootics.

Richardson’s ground squirrels (Urocitellus richardsonii) are associated primarily with intermediate levels of grassland, clay loam soils, and human development in Canadian mixed-grass prairies

“…Clay loam soils have almost equal parts of sand and silt, with a slightly higher percentage of clay. The higher percentage of clay in the soil may confer the advantage of a more stable and long-term burrow, while the equal percentages of sand and silt may make the initial excavating of the burrow easier and more energy efficient (Levick et al 2015). This corresponds well to the findings of Proulx et al ( 2012), who showed that ground squirrels were mostly limited to the Brown soil zone which is typically composed of loam or coarser texture soils.…”

Living with plague: Lessons from the Soviet Union’s antiplague system

“…Great gerbil burrows vary in depth up to 3 m, and the depth is critical to flea survival, with shallow burrows less favorable for fleas (96, 97). Burrows in sandy soil and those surrounded by vegetation may be more likely to contain plague-bearing fleas (9). Using PCR assays (98), Y. pestis can be more sensitively detected in burrow-collected fleas, and flea species more likely to contribute to plague persistence locally can be identified.…”

“…Y. pestis has been detected in over 280 species and subspecies of fleas associated with rodent colonies in these areas (8). While the factors constraining where plague reservoirs may exist are not fully known (9), certain rodent species appear to be cornerstone hosts for the disease (10). In our current understanding, plague persists within these ecosystems in a continuous exchange of Y. pestis between rodent individuals, with fleas as the main vector (11).…”

The Ili River Delta: Holocene Hydrogeological Evolution and Human Colonization

“…The study sites concerned randomly chosen 500 m × 500 m (25 ha) squares spread over 6 sectors (see Fig. 4.2) (Levick et al 2015).…”