Mineral levels in study elk.

Treponeme-associated hoof disease (TAHD) is a debilitating disease of free-ranging elk (Cervus canadensis) in the northwestern U.S. While treponemes are associated with lesions, the etiology and transmissibility between elk are unknown. Our objective was to determine whether the disease can be environmentally transmitted to captive elk. Four individually housed treatment elk and 2 control elk were challenged with soil mixed with inoculum prepared from free-ranging elk hooves from TAHD-positive elk or autoclaved hooves from normal elk, respectively. The inoculum for each group was applied to the interdigital space and added to pre-existing soil in each pen. Eight challenges were conducted at 1–4-week intervals and lesion development was assessed during a 138-day challenge period that was followed by a 170-day monitoring period to document lesion progression. All treatment elk, but no control elk, developed gross and histologic lesions consistent with TAHD. Treponema phylotypes similar to those in bovine digital dermatitis in cattle were detected using 16S rRNA gene amplicon sequencing from lesions in all treatment elk, but no control elk, during the challenge period. Lesions progressed from ulcerations in the interdigital space to extensive ulceration and underrunning of the hoof capsule by 35 and 173 days following the initial inoculation, respectively. Lameness in treatment elk was correlated with lesion development (R = 0.702, p≤0.001), and activity of infected elk was reduced during the challenge (p≤0.001) and monitoring periods (p = 0.004). Body condition was significantly lower in treatment than control elk 168 days following the initial inoculation (p = 0.05) and at each individual elk’s study endpoint (p = 0.006). Three of 4 treatment elk were euthanized when they reached humane endpoints, and one elk recovered. These results provide direct evidence that TAHD is a transmissible infectious disease in elk. As such, actions that reduce transmission risk can support disease management and prevention.密螺旋体相关蹄病（Treponeme-associated hoof disease, TAHD）是美国西北部野生北美马鹿（Cervus canadensis）的一种致残性疾病。尽管密螺旋体与病变形成存在关联，但该病的病因学机制以及马鹿个体间的传播性仍未明确。本研究旨在明确该病是否可通过环境途径传播给圈养北美马鹿。实验设置4只单独饲养的受试马鹿与2只对照马鹿，分别暴露于两种混合土壤：受试组土壤由TAHD阳性野生马鹿蹄部制备的接种物混合而成，对照组土壤则由正常马鹿蹄部经高压灭菌处理后的材料混合制成。两组接种物均涂抹于受试马鹿的蹄间隙，并添加至各圈舍原有的土壤中。实验共开展8次接种操作，间隔为1~4周；在为期138天的接种阶段内对病变发展情况进行评估，随后再开展170天的监测阶段以记录病变的进展过程。所有受试马鹿均出现了与TAHD相符的大体病理学与组织病理学病变，而对照马鹿未出现任何此类病变。在接种阶段，研究人员通过16S rRNA基因扩增子测序（16S rRNA gene amplicon sequencing），在所有受试马鹿的病变组织中检测到与牛指（趾）间皮炎（bovine digital dermatitis）相关的密螺旋体系统型，而对照马鹿的病变组织中未检测到此类类群。在首次接种后的第35天与第173天，病变分别从蹄间隙溃疡发展为大范围溃疡，并伴随蹄匣下侵性破坏。受试马鹿的跛行症状与病变发展呈显著正相关（相关系数R=0.702，p≤0.001）；且感染马鹿的活动量在接种阶段（p≤0.001）与监测阶段（p=0.004）均显著降低。在首次接种后的第168天，受试马鹿的体况评分显著低于对照马鹿（p=0.05）；且在每只受试马鹿的实验终点时，该差异依然显著（p=0.006）。4只受试马鹿中有3只因达到人道安乐死标准被实施安乐死，剩余1只马鹿康复。本研究结果直接证实TAHD是马鹿的一种可传播传染性疾病。据此，采取降低传播风险的措施可有效助力该病的防控与预防。