Estimating the risk of elk-to-livestock brucellosis transmission in Montana

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 Montana, 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. To help mitigate potential conflict, we identified how spillover risk changes through space and time using a combination of elk population, disease, and movement data. We developed resource selection functions using telemetry data from 223 female elk to predict the relative probability of female elk occurrence on a daily basis during the 15 February-30 June transmission risk period. We combined these spatiotemporal predictions with elk seroprevalence, demography, and abortion timing data to identify when and where abortions (the primary transmission route of brucellosis) were most likely to occur. Additionally, we integrated these predictions with spatiotemporal data on livestock distribution to estimate the daily risk of livestock encountering brucellosis-induced elk abortions. We estimated that a minimum of ~17,500 adult female elk lived within our study area, which resulted in a conservative estimate of ~525 brucellosis-induced abortions each year. We predicted that approximately half of the transmission events occurred on livestock properties and 98% of those properties were private ranchlands as opposed to state or federal grazing allotments. Our fine-resolution (250-m spatial, 1-day temporal), large-scale (17,732 km2) 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.