Lesion Material From Treponema-Associated Hoof Disease of Wild Elk Induces Disease Pathology in the Sheep Digital Dermatitis Model

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.

Treatment of digital dermatitis using salicylic acid in European bison (Bison bonasus) reveals promising results

“…As a species that is regularly transferred between institutions and rewilded in Europe, preventing the transmission of infectious diseases is of particular importance ( 43 ). The rapid spread of Treponema -associated hoof disease in free-living elk illustrates the difficulty of controlling this infectious hoof disease once it has established in the population ( 44 ).…”

Correlation of lesion severity with bacterial changes in Treponeme-Associated Hoof Disease from free-roaming wild elk (Cervus canadensis)

“…PCR for Treponema medium, Treponema pedis, Treponema phagedenis, Treponema vincentii , Treponema denticola, Treponema brennaborense and Fusobacterium necrophorum was performed on n = 158, including healthy, lesion and contralateral samples, in a two-stage nested PCR assay as previously described [ 1 , 17 , 18 ]. Positive controls were genomic DNA purified from each respective bacterial species.…”

“…Recent meta-analysis of bovine digital dermatitis microbiota concluded that bacteria from the Treponema genus were highly abundant in bacterial populations in DD positive skin samples as compared to DD negative skin samples, implicating the genus as a core pathogen for lesion development [ 23 ]. There is evidence from numerous studies that DD and DD-like diseases (CODD & TAHD) are polymicrobial and that a core consortium of Fusobacterium spp., Bacteroides spp., Porphyromonas spp., and Mycoplasma spp., may also contribute to lesion development, although reported bacterial population abundances within lesions differ between published studies [ 1 , 9 , 11 , 13 , 17 , 23 , 24 ]. Molecular techniques have confirmed observations of spirochetal bacteria infiltrates deeper within the lesions, with cocci and fusiform rods forming matts on the outer epithelium in silver-stained tissue sections [ 1 , 4 , 25 ].…”

“…Histopathology was used to confirm any potentially degraded samples identified by visual inspection. Presence of spirochetal forms and key markers of TAHD (inflammatory cells, acanthosis, and keratin crust thickening) as defined in previous studies was used to categorize lesions between grade 0 and grade 1 (Supplementary Material 3) [ 1 , 17 ].…”

An experimental model to induce digital dermatitis in beef calves

“…Wilson-Welder et al [ 27 ] inoculated crossbred sheep with bovine derived DD inoculum and achieved an 88% induction over a 28-day protocol, and contagious ovine digital dermatitis was induced in 15 of 30 experimental sheep [ 28 ]. Most recently, Wilson-Welder et al [ 29 ] using lesion material obtained from wild elk induced treponeme-associated hoof disease in sheep by way of a sheep DD model. To date there have been no published reports that have attempted to experimentally induce DD in beef cattle.…”