Background

The distribution of resources can affect animal range sizes, which in turn may alter infectious disease dynamics in heterogenous environments. The risk of pathogen exposure or the spatial extent of outbreaks may vary with host range size. This study examined the range sizes of herbivorous anthrax host species in two ecosystems and relationships between spatial movement behavior and patterns of disease outbreaks for a multi-host environmentally transmitted pathogen.

Methods

We examined range sizes for seven host species and the spatial extent of anthrax outbreaks in Etosha National Park, Namibia and Kruger National Park, South Africa, where the main host species and outbreak sizes differ. We evaluated host range sizes using the local convex hull method at different temporal scales, within-individual temporal range overlap, and relationships between ranging behavior and species contributions to anthrax cases in each park. We estimated the spatial extent of annual anthrax mortalities and evaluated whether the extent was correlated with case numbers of a given host species.

Results

Range size differences among species were not linearly related to anthrax case numbers. In Kruger the main host species had small range sizes and high range overlap, which may heighten exposure when outbreaks occur within their ranges. However, different patterns were observed in Etosha, where the main host species had large range sizes and relatively little overlap. The spatial extent of anthrax mortalities was similar between parks but less variable in Etosha than Kruger. In Kruger outbreaks varied from small local clusters to large areas and the spatial extent correlated with case numbers and species affected. Secondary host species contributed relatively few cases to outbreaks; however, for these species with large range sizes, case numbers positively correlated with outbreak extent.

Conclusions

Our results provide new information on the spatiotemporal structuring of ranging movements of anthrax host species in two ecosystems. The results linking anthrax dynamics to host space use are correlative, yet suggest that, though partial and proximate, host range size and overlap may be contributing factors in outbreak characteristics for environmentally transmitted pathogens.

We compiled movement data from GPS (Global Positioning System) collars including newly collected and previously published datasets on springbok (Antidorcas marsupialis) from Etosha National Park, Namibia, impala (Aepyceros melampus) and African buffalo (Syncerus caffer) from Kruger National Park, South Africa, and greater kudu (Tragelaphus strepsiceros), blue wildebeest (Connochaetes taurinus), and plains zebra (Equus quagga) from both parks between 2006 – 2020. Newly collected data included movement datasets on kudu, wildebeest and zebra (2018–2020) in Etosha and impala and kudu in Kruger. Details of the numbers, time periods and data sources of these movement data can be found in the corresponding research paper. 

Because of different sampling intensities and irregular intervals of the telemetry data, we thinned the data to three readings a day for more comparable relocation data across different species and tracking periods among species. We then prepared three different datasets at bimonthly, monthly and seasonal scales for each species by park and further prepared a fourth dataset at seasonal scales with only individuals tracked across at least three seasons. Details of dataset preparation can be found in the corresponding paper. The data here are thinned movement datasets.

These files include:

1. Thinned movement datasets

2. Shapefiles for Etosha and Kruger boundaries and pains in Etosha

3. R code for analyses