Abstract
AimThe spatial structure of a population can strongly influence the dynamics of infectious diseases, yet rarely is the underlying structure quantified. A case in point is plague, an infectious zoonotic disease caused by the bacterium Yersinia pestis. Plague dynamics within the Central Asian desert plague focus have been extensively modelled in recent years, but always with strong uniformity assumptions about the distribution of its primary reservoir host, the great gerbil (Rhombomys opimus). Yet, while clustering of this species’ burrows due to social or ecological processes could have potentially significant effects on model outcomes, there is currently nothing known about the spatial distribution of inhabited burrows. Here, we address this knowledge gap by describing key aspects of the spatial patterns of great gerbil burrows in Kazakhstan.LocationKazakhstan.MethodsBurrows were classified as either occupied or empty in 98 squares of four different sizes: 200 m (side length), 250 m, 500 m and 590–1020 m. We used Ripley's K statistic to determine whether and at what scale there was clustering of occupied burrows, and semi‐variograms to quantify spatial patterns in occupied burrows at scales of 250 m to 9 km.ResultsSignificant spatial clustering of occupied burrows occurred in 25% and 75% of squares of 500 m and 590–1020 m, respectively, but not in smaller squares. In clustered squares, the clustering criterion peaked around 250 m. Semi‐variograms showed that burrow density was auto‐correlated up to a distance of 7 km and occupied density up to 2.5 km.Main conclusionsThese results demonstrate that there is statistically significant spatial clustering of occupied burrows and that the uniformity assumptions of previous plague models should be reconsidered to assess its significance for plague transmission. This field evidence will allow for more realistic approaches to disease ecology models for both this system and for other structured host populations.
Highlights
The social or spatial structure of wildlife populations has significant implications for the invasion (Keeling, 1999), spread (Grenfell et al, 2001) and persistence of infectious diseases (Keeling & Gilligan, 2000)
These results demonstrate that there is statistically significant spatial clustering of occupied burrows and that the uniformity assumptions of previous plague models should be reconsidered to assess its significance for plague transmission
Knowledge of the underlying spatial structure of wildlife populations is key to understanding and modelling how an infectious disease spreads through host populations
Summary
The social or spatial structure of wildlife populations has significant implications for the invasion (Keeling, 1999), spread (Grenfell et al, 2001) and persistence of infectious diseases (Keeling & Gilligan, 2000). Far from being uniformly distributed in the environment, many wildlife populations resemble a metapopulation, i.e. a network of subpopulations which are connected to varying degrees by temporary movements or dispersal of individuals (Hanski, 1999; Leibold et al, 2004) This network structure has significant implications for the spread of an infection, as transmission within a population depends on group size, the frequency of individual movements between groups, and the time the disease persists within each group (Grenfell & Harwood, 1997; Keeling & Gilligan, 2000; Keeling & Rohani, 2002; Cross et al., 2007; Jesse & Heesterbeek, 2011). Much of this work has focused on the Central Asian desert plague focus in south-east Kazakhstan, where the burrowing great gerbil, Rhombomys opimus (Lichtenstein, 1823), is the main host and Xenopsylla spp. fleas are the primary vectors
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