Modeling elk‐to‐livestock transmission risk to predict hotspots of brucellosis spillover

Abstract

Wildlife reservoirs of infectious disease are a major source of human-wildlife conflict because of the risk of potential spillover associated with commingling of wildlife and livestock. In the Greater Yellowstone Ecosystem, the presence of brucellosis (Brucella abortus) in free-ranging elk (Cervus canadensis) populations is of significant management concern because of the risk of disease transmission from elk to livestock. We identified how spillover risk changes through space and time by developing resource selection functions using telemetry data from 223 female elk to predict the relative probability of female elk occurrence daily during the transmission risk period. We combined these spatiotemporal predictions with elk seroprevalence, demography, and transmission timing data to identify when and where abortions (the primary transmission route of brucellosis) were most likely to occur. Additionally, we integrated our predictions of transmission risk with spatiotemporal data on areas of potential livestock use to estimate the daily risk to livestock. We predicted that approximately half of the transmission risk occurred on areas where livestock may be present (i.e., private property or grazing allotments). Of the transmission risk that occurred in livestock areas, 98% of it was on private ranchlands as opposed to state or federal grazing allotments. Disease prevalence, transmission timing, host abundance, and host distribution were all important factors in determining the potential for spillover risk. Our fine-resolution (250-m spatial, 1-day temporal), large-scale (17,732 km 2 ) predictions of potential elk-to-livestock transmission risk provide wildlife and livestock managers with a useful tool to identify higher risk areas in space and time and proactively focus actions in these areas to separate elk and livestock to reduce spillover risk. Ó 2019 The Authors. The Jo urnal o f

Elk migration influences the risk of disease spillover in the Greater Yellowstone Ecosystem

“…Within the risk period, we defined winter ( 15February-31 March; elk on winter range), spring (1 April-31 May; elk migrating to summer range) and summer (1 June-30 June; elk on summer range) seasons. We based our seasons upon elk movement and aggregation patterns, the typical timing of snow melt and green-up, and to be consistent with seasons defined in our previous work (Rayl et al, 2018(Rayl et al, , 2019…”

“…Therefore, we relied on an approach that coupled spatiotemporal estimates of elk and livestock distribution with disease and demographic data to quantify spillover risk. To evaluate the role of migration and weather variability in the risk of brucellosis transmission from elk to livestock, we followed the same general approach of Merkle et al (2018) and Rayl et al (2019). We (a) identified migrant and resident groups from each elk herd, (b) estimated the occurrence of migrant and resident groups using resource selection functions (RSFs; Manly et al, 2002), (c) combined our RSF elk occurrence predictions with estimates of adult female elk abundance, seroprevalence, pregnancy rates and transmission timing to predict the daily relative risk of brucellosis-induced abortion events, which is proportional to the number of brucellosis-induced abortion events and (d) estimated the proportion of transmission risk from migrant and resident elk occurring on public and private lands and within private ranchland and federal and state livestock allotments during low, average and heavy snowfall years.…”

“…The timing of spring elk migration in the GYE is influenced by snow conditions and plant phenology, and coincides with the period of greatest transmission risk for brucellosis (Cross et al, 2015;Jones et al, 2014;Rickbeil et al, 2019;White et al, 2010). At the onset of the transmission risk period, migrant and resident elk occur together on lower elevation winter ranges that are often managed as private ranchlands (Rayl et al, 2019). As the transmission period progresses, however, migrant elk begin moving 10-100 s of kilometres to summer range on publicly owned lands at higher elevations, thereby decoupling their distribution from resident elk (Barker et al, 2019;Rickbeil et al, 2019;White et al, 2010).…”

Confronting models with data: the challenges of estimating disease spillover

“…In addition, for regions where no movement data are available, one would have to infer movement using data from other regions. Rayl et al [25] did not model this movement across regions, but instead assumed no movement where the data were lacking. In this study, uncertainties were not integrated and errors were not propagated comprehensively.…”

Dynamic and integrative approaches to understanding pathogen spillover

“…Mycoplasma ovipneumoniae from domestic sheep to bighorn sheep [ 7 ]) and the agricultural sector (e.g. Brucella abortus from elk to cattle [ 8 ]).…”