Abstract
A hoof disease among wild elk (Cervus elaphus) in the western United States has been reported since 2008. Now present in Washington, Oregon, Idaho, and California, this hoof disease continues to spread among elk herds suggesting an infectious etiology. Causing severe lesions at the hoof-skin junction, lesions can penetrate the hoof-horn structure causing severe lameness, misshapen hooves, and in some cases, sloughed hooves leaving the elk prone to infection, malnutrition, and premature death. Isolated to the feet, this disease has been termed treponeme-associated hoof disease due to the numerous Treponema spp. found within lesions. In addition to the Treponema spp., treponeme-associated hoof disease shares many similarities with digital dermatitis of cattle and livestock including association with several groups of anaerobic bacteria such as Bacteroides, Clostridia, and Fusobacterium, neutrophilic inflammatory infiltrate, and restriction of the disease to the foot and hoof tissues. To determine if there was a transmissible infectious component to this disease syndrome, elk lesion homogenate was used in a sheep model of digital dermatitis. Ten animals were inoculated with lesion material and lesion development was followed over 7 weeks. Most inoculated feet developed moderate to severe lesions at 2- or 4-weeks post-inoculation timepoints, with 16 of 18 feet at 4 weeks also had spirochetes associated within the lesions. Histopathology demonstrated spirochetes at the invading edge of the lesions along with other hallmarks of elk hoof disease, neutrophilic inflammatory infiltrates, and keratinocyte erosion. Treponema-specific PCR demonstrated three phylotypes associated with elk hoof disease and digital dermatitis were present. Serum of infected sheep had increased anti-Treponema IgG when compared to negative control sheep and pre-exposure samples. Analysis of the bacterial microbiome by sequencing of the bacterial 16S rRNA gene showed a community structure in sheep lesions that was highly similar to the elk lesion homogenate used as inoculum. Bacteroidies, Fusobacterium, and Clostridia were among the bacterial taxa overrepresented in infected samples as compared to negative control samples. In conclusion, there is a highly transmissible, infectious bacterial component to elk treponeme-associated hoof disease which includes several species of Treponema as well as other bacteria previously associated with digital dermatitis.
Highlights
In 2008 increased numbers of limping elk (Cervus elaphus) and an increased presence of deformed hoofs were observed in southwestern Washington State
Plots showing the representation of individual operational taxonomic units (OTUs) by sample and relative abundance for the other 40 OTUs can be found in Supplementary Figures S4-S6. The goal of this experiment was to evaluate the ability of TAHD lesion material from elk to induce disease in a sheep model
Lesions contained spirochete shaped bacteria and molecular analysis determined that Treponema species or phylotypes typically associated with TAHD and livestock digital dermatitis (DD) were associated with lesions
Summary
In 2008 increased numbers of limping elk (Cervus elaphus) and an increased presence of deformed hoofs were observed in southwestern Washington State. Throughout the following decade, cases were confirmed all along the western range of the Cascade mountains, further north into Washington, throughout neighboring Oregon state, and as far south as northern California. Cases have been confirmed in far eastern Washington state, and adjacent Idaho, representing movement of this disease across to the eastern side of the Cascade mountains. Reports rapidly increased over a short period of time radiating from the region where lesions were first observed [1]. Bacterial species isolated from the hoof lesions were similar to those present in polymicrobial digital dermatitis (DD) of livestock [2, 3]. Treponema isolates from elk hoof lesions were determined to be the same three phylotypes as isolated from DD lesions of cattle and sheep [2, 4]
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