Margaret A. Wild

Treponeme-associated hoof disease (TAHD) is an emerging, polybacterial infection that causes painful foot lesions and lameness in free-ranging elk ( Cervus canadensis ) across the northwestern USA. Although TAHD is associated with multiple Treponema species and other anaerobic bacteria, current understanding of disease etiology is limited and based primarily on cross-sectional analyses of naturally infected elk, in which lesions were examined at single time points using histopathology and 16S rRNA gene sequencing. Our objective was to develop a rapid and reliable experimental infection model to study TAHD pathogenesis in captive elk under controlled conditions. Inoculum consisting of macerated lesion tissue and mixed cultures of Treponema spp. and other anaerobic bacteria derived from TAHD lesions was applied onto abraded interdigital skin on the hind feet of five treatment elk. Inoculated feet were wrapped to expedite lesion development. Over the 7 week study period, all inoculated feet (10/10) developed interdigital erosions consistent with mild to moderate TAHD lesions observed in free-ranging elk. Lesions were observed on the majority of inoculated feet (9/10) after 28 days, coinciding with concurrent 16S rRNA gene amplicon sequencing detection of three putative pathogens of TAHD: Treponema , Fusobacterium, and Mycoplasma . In contrast, mock-inoculated control elk feet did not exhibit pathological or microbiological changes indicative of TAHD. This experimental infection model provides a valuable platform to investigate the complex interactions between the host, pathogens, and environmental factors that influence TAHD susceptibility, lesion progression, and disease transmission. IMPORTANCE: Our study details a new approach for consistent and rapid induction of treponeme-associated hoof disease (TAHD) lesions in captive elk. TAHD is an emerging polybacterial disease of conservation concern that causes chronic lameness and debilitation in free-ranging elk across the northwestern USA. We rapidly and reliably reproduced TAHD lesions following challenge with inoculum consisting of macerated lesion tissue and mixed cultures of Treponema spp. and other anaerobic bacteria. This experimental infection model provides a valuable platform for investigation of the complex interactions between the host, pathogens, and environmental factors influencing TAHD susceptibility, lesion progression, and disease transmission in elk.

Treponeme-associated hoof disease (TAHD) is an emerging disease of free-ranging elk (Cervus canadensis) in the northwestern United States. Affected elk develop chronic foot lesions, lameness, debilitation, and an apparent increase in mortality, but the onset of lameness and associated changes in activity are not fully understood. We evaluated the accuracy of a newly developed leg-mounted tri-axial accelerometer monitor (Advanced Telemetry Systems) on captive elk and collected monitor-derived data to assess activity before and during an experimental TAHD challenge. Monitors provided reliable data with 85% overall accuracy of the continuous onboard classification of activity as standing, moving, or bedded against direct visual observation using seven healthy elk. Further, following TAHD challenge, monitor-derived data were able to detect that treatment elk exhibiting abnormal locomotion spent more time bedded and less time moving or standing. During the challenge period, treatment elk spent roughly 10% more of the day bedded than control elk. These findings suggest that leg-mounted activity monitors can detect changes in elk activity and may serve as a useful tool for future wildlife disease monitoring efforts.

Environments can shape the occurrence and extent of disease outbreaks in wildlife. We studied the effects of environmental features on the occurrence of treponeme‐associated hoof disease (TAHD), an emerging infectious disease of free‐ranging elk ( Cervus canadensis ), in southwestern Washington, USA. During the 2016–2022 harvest seasons, successful elk hunters returned mandatory harvest reports and noted the presence or absence of hoof abnormalities indicative of TAHD. We used generalized linear models and an information‐theoretic approach to model selection to relate (1) the spatial distribution of hoof abnormalities to features of landscapes (land cover, topography, and soil characteristics) and (2) the temporal distribution of hoof abnormalities to precipitation during the year preceding the harvest season. The probability of hoof disease increased with soil clay content and proportion of agricultural land (88% of model weight). We found no conclusive evidence for an effect of precipitation on the occurrence of TAHD, but this could relate to relatively high annual precipitation (>140 cm) in the study area. Nevertheless, disease cases may have been negatively associated with precipitation during February–June (55% of model weight). Soils and land management practices may increase the risk of hoof disease by promoting the survival of pathogens that cause TAHD, the susceptibility of elk to infection, or the intensity of pathogen transmission among elk when congregated. Focusing on areas where the risk of disease is greatest may facilitate the detection of TAHD during surveillance. Likewise, removing infected elk and dispersing uninfected elk from areas with the greatest risk of disease may enhance the effectiveness of efforts to reduce transmission. Basing this work on the knowledge that disease risk is modified by factors of hosts, pathogens, and environments, this study serves as an application of the epidemiological triad framework to better understand the ecology and epidemiology of an emerging infectious disease in wildlife.

Treponeme-associated hoof disease (TAHD) is an emerging infectious disease in free-ranging elk ( Cervus canadensis ) characterized by ulcerative and necrosuppurative pododermatitis with spirochete bacteria that leads to lameness and apparent increased mortality. While TAHD is hypothesized to have a polybacterial etiology, the causative agents remain poorly characterized, particularly across its geographic range. In this study, we developed a histologic categorization system for hoof lesions and employed 16S rRNA gene amplicon sequencing to characterize bacterial communities in samples from 129 free-ranging elk across regions with endemic or sporadic TAHD and where TAHD remains undetected. Differential abundance analysis revealed strong associations between TAHD-positive lesions and the bacterial genera Treponema , unidentified Spirochaetaceae , Mycoplasma , and Fusobacterium , along with their respective families and amplicon sequence variants. Many of these TAHD-associated operational taxonomic units (OTUs) were also more frequently detected at increased abundance in more severe, histologic lesions of pododermatitis. Correlation analysis demonstrated a strong positive association between Treponema and Mycoplasma in TAHD lesions, suggesting a more significant role of Mycoplasma in TAHD’s etiology than previously recognized. Additionally, we identified novel TAHD-associated OTUs, including Corynebacterium freneyi-xerosis , that warrant further investigation. Comparative analysis of TAHD-positive lesions from endemic and sporadic areas revealed minimal differences in the microbial community. These findings advance our understanding of the bacterial contributors to TAHD, highlighting putative pathogens for further investigation and as potential targets for diagnostic development. IMPORTANCE: While detection of Treponema is a hallmark of treponeme-associated hoof disease (TAHD), a comprehensive understanding of other bacterial contributors is necessary to improve diagnostic testing and inform control measures. Our study confirmed strong associations between Spirochaetaceae and TAHD lesions and revealed a previously underappreciated role of Mycoplasma in TAHD’s etiology. Treponema and Mycoplasma were significantly enriched in TAHD-positive lesions, absent from TAHD-negative tissues, and strongly and positively correlated with each other, suggesting a potential synergistic relationship. By developing and applying a histologic categorization system, we characterized shifts in bacterial communities as lesion severity progressed. Comparisons of TAHD-positive lesions from endemic and sporadic regions revealed minimal differences in the microbial composition, indicating strong geographic consistency. These findings enhance our understanding of TAHD’s etiology and provide a foundation for future research, including the development of improved diagnostic tests and targeted disease management strategies.

Pododermatitis, also known as treponeme-associated hoof disease (TAHD), presents a significant challenge to elk ( Cervus canadensis ) populations in the northwestern USA, with Treponema spp. consistently implicated in the lesion development. However, identifying species-specific Treponema strains from these lesions is hindered by its culture recalcitrance and limited genomic information. This study utilized shotgun sequencing, in silico genome reconstruction, and comparative genomics as a culture-independent approach to identify metagenome-assembled Treponema genomes (MATGs) from skin scraping samples collected from captive elk experimentally challenged with TAHD. The genomic analysis revealed 10 new MATGs, with 6 representing novel genomospecies associated with pododermatitis in elk and 4 corresponding to previously identified species —Treponema pedis and Treponema phagedenis . Importantly, genomic signatures of novel genomospecies identified in this study were consistently detected in biopsy samples of free-ranging elk diagnosed with TAHD, indicating a potential etiologic association. Comparative metabolic profiling of the MATGs against other Treponema genomes showed a distinct metabolic profile, suggesting potential host adaptation or geographic uniqueness of these newly identified genomospecies. The discovery of novel Treponema genomospecies enhances our understanding of the pathogenesis of pododermatitis and lays the foundation for the development of improved molecular surveillance tools to monitor and manage the disease in free-ranging elk. IMPORTANCE: Treponema spp. play an important role in the development of pododermatitis in free-ranging elk; however, the species-specific detection of Treponema from pododermatitis lesions is challenging due to culture recalcitrance and limited genomic information. The study utilized shotgun sequencing and in silico genome reconstruction to identify novel Treponema genomospecies from elk with pododermatitis. The discovery of the novel Treponema species opens new avenues to develop molecular diagnostic and epidemiologic tools for the surveillance of pododermatitis in elk. These findings significantly enhance our understanding of the genomic landscape of the Treponemataceae consortium while offering valuable insights into the etiology and pathogenesis of emerging pododermatitis in elk populations.

Treponeme-associated hoof disease (TAHD) is an emerging disease of conservation concern in elk (Cervus canadensis) in the Northwest USA. Elk with TAHD exhibit characteristic hoof lesions that are often accompanied by lameness and limping. The gold standard approach traditionally used for infectious disease surveillance is laboratory confirmation, which for TAHD is a histologic examination of abnormal elk hooves submitted by wildlife agencies. Diagnostic evaluation affords certainty in confirming TAHD; however, these examinations are also labor and resource intensive, and therefore, not conducive to the collection of sufficient data for epidemiologic investigations. In response, two community science (CS) surveillance strategies have been implemented in Washington State: public observations of limping elk from a web-based reporting tool and hunter reports of hoof abnormalities on harvested elk. Surveillance using CS strategies can be implemented widely and may be useful for describing broad distributional patterns of TAHD, despite their unknown relationship to laboratory-confirmed cases. We described and compared the spatialtemporal distribution of TAHD in western Washington game management units (GMU) using the two CS strategies to assess congruences and discrepancies between observed patterns. We used spatial scan statistics to identify possible core-affected and newly emerging areas at the GMU level. Lastly, we contrasted CS observations against confirmed case data to examine possible delays in TAHD detection and co-occurrence among surveillance strategies. We found public observations of limping elk often predated TAHD confirmations in GMUs by several years, while hunter-reported abnormalities predated confirmations in GMUs by several months. High co-occurrence between the presence of apparent and confirmed cases under different surveillance strategies further supports the use of CS sources. This study capitalizes on wide-reaching CS data to provide new and complementary epidemiological information that can help guide future surveillance, management, and research efforts for this novel elk hoof disease.

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.

A common understanding and clear process to apply the Animal Welfare Act (AWA) to wildlife‐related activities is crucial to promote animal welfare when conducting wildlife research and for streamlining review by an Institutional Animal Care and Use Committee (IACUC). Current interpretation of the AWA and United States government policies advise that wildlife research activities be reviewed for compliance by an IACUC; however, guidance regarding which wildlife activities are categorized as research and therefore subject to review and oversight is limited. In our opinion and experience, this lack of clarity creates a challenge, particularly for natural resource agencies that conduct a range of wildlife activities, to ensure that research is properly identified for IACUC review and differentiated from management activities that are exempt from review. To fill the gap in current guidance, we propose a decision‐making model that clarifies research and management activities. We apply our model to case studies involving wildlife to highlight nuanced differences between the 2 types of activities. Wildlife agencies conducting potentially regulated activities could use this adaptable model, which has been successfully employed by the National Park Service IACUC, to clarify when the AWA might apply, streamline IACUC reviews, and promote welfare of wildlife.

"Investigate, discover, solve, repeat" published on 10 Jun 2023 by American Veterinary Medical Association.