Use of biosecurity practices to prevent chronic wasting disease in Minnesota cervid herds

The objective of this study was to evaluate biosecurity practices related to chronic wasting disease (CWD) transmission pathways and prevention in active cervid herds in Minnesota in 2019 by species, size and location of herds. A self-administered questionnaire was sent to all cervid producers in Minnesota to gather demographic, management, and biosecurity practices. Among producers (N=136), 63.2 % raised predominantly deer species and 36.8 % raised predominantly elk or reindeer. Survey responses were analyzed by herd species (deer or elk/reindeer), herd size (<20 or ≥20 animals), and location (southeast Minnesota or rest of the state) to determine statistical differences between strata. In terms of CWD transmission risks from other farmed cervids, 40.4 % (95 % Confidence Intervals (CI) 32.1–48.8) of Minnesota producers stated they introduced new cervids to the operation in the previous 3 years, though there were minimal other forms of direct contact. A higher percentage of larger sized elk/reindeer herds reported practices that indicate potential for indirect contact with other farmed cervids. Vehicles or trailers that entered the farm were used to transport other live cervids, cervid carcasses, or cervid body parts in past 3 years in 64.3 % (95 % CI 46.3–82.3) of larger elk/reindeer herds compared to 13.6 % (95 % CI 4.7–22.4) of smaller deer herds.

For CWD transmission risks from wild cervids, limited potential direct contact was reported. Among all producers, 9.6 % (95 % CI 4.6–14.6) reported farmed cervid escapes in the past 3 years (even temporarily) and 0.7 % (95 % CI 0.0–2.2) of producers reported wild white-tailed deer (WTD) inside perimeter fencing. Additionally, 24.3 % (95 % CI 17.0–31.6) of producers observed wild WTD near the perimeter fencing in the past 12 months and 18.7 % (95 % CI 12.0–25.3) reported use of double perimeter fencing, indicating frequent proximity to wild deer and potential for direct and/or indirect contact exposures. Further, 14.3 % (95 % CI 6.7–21.9) of deer herds and 30.0 % (95 % CI 17.1–42.9) of elk herds reported potential access of wild cervids to hay/silage while stored on the farm, with similar results comparing smaller and larger size strata (13.8 % (95 % CI 6.1–21.4) and 29.6 % (95 % CI 17.3–42.0), respectively). Contact through hunting or taxidermy practices occurred infrequently, with the exception of 20.1 % (95 % CI 13.3–27.0) of producers reporting bringing outside hunted cervid parts/carcasses onto property in the past 3 years.

Overall, results identified direct and indirect contact exposures from both farmed and wild cervids to Minnesota herds, with many producers reporting potential contact with wild cervids through direct and multiple indirect pathways. Many of these indirect exposures to wild and farmed cervids varied by herd size and species strata. Better understanding of these potential CWD transmission pathways and how differences between herd size and species affect these pathways will facilitate development of more effective biosecurity programs for cervid herds.