The dysbiosis of ovine foot microbiome during the development and treatment of contagious ovine digital dermatitis

Etiology and epidemiology of digital dermatitis in Australian dairy herds

Bovine digital dermatitis (BDD) is an important cause of lameness in dairy cows worldwide. However, very little is known about this disease in Australian herds, which are predominantly managed on pasture. The primary objectives of this cross-sectional study were to describe the presence and prevalence of BDD in Australian dairy herds and to characterize the microbiota of healthy skin and M4 lesions of BDD-affected, pasture-managed cows. Cows from 71 dairy herds were examined at milking time to identify the presence of BDD lesions. True prevalence was estimated using Bayesian methods with informative priors for sensitivity and specificity. Biopsy samples (n = 60) were collected from cows with and without BDD lesions in 7 pasture-based herds. The microbiota in the superficial and deep strata of each tissue biopsy were characterized via sequencing of the V3-V4 region of the bacterial ribosomal RNA gene. Lesions were detected in 1,817 (11.5%) of 15,813 cows and in 68 of 71 (95.8%) herds. The median herd-level apparent and true prevalences of BDD were 8.5% and 18.1%, respectively, but prevalences varied considerably between farms. On farms with BDD, M4 lesions accounted for 70% to 100% of all lesions (interquartile range = 95.1%-100%, median = 100%); M2 lesions (i.e., large ulcerative lesions) were observed at low prevalence (<2.2%) in the few herds (7/71, 9.9%) where they were found. There was a significant difference in the composition of the microbiota between healthy skin and M4 lesions but not between superficial and deep tissue layers. Several gut- and effluent-associated bacterial taxa, including Lentimicrobium and Porphyromonas, which have previously been associated with BDD, were abundant in BDD lesions but not in control biopsies. Our study supports the idea that such taxa are involved in, although possibly not essential to, lesion development and persistence in pasture-managed cows in Australia. Our results also suggest that Dichelobacter may contribute to the disease process. We conclude that BDD is likely to occur in most Australian dairy farms, but that further studies are needed to identify its effect on cow welfare and productivity. Further investigation of the etiology of BDD in Australian dairy herds is also necessary to inform prevention and control strategies.

Multilocus sequence typing of pathogenic treponemes isolated from contagious ovine digital dermatitis stage five lesions: Implications for disease transmission dynamics

Contagious ovine digital dermatitis (CODD) causes a severe, infectious foot disease and lameness of sheep, is common within the UK and is now also emerging in other countries. As well as causing severe animal welfare issues, huge economic losses emerge from the disease due to weight loss/lack of weight gain, and veterinary treatments. CODD lesion progress is measured, with a scoring system from 1 (early lesions) to 5 (healed). Here, using samples from an experimental flock infected by natural means, samples were taken from CODD stage 5 lesions, post treatment, and subjected to bacterial isolation and MLST using previously published methods. Sequences were compared to others from the same flock, and those from previous studies. All CODD 5 lesions produced viable Treponema spp. bacteria. High levels of variation of bacteria were seen, with 12 sequence types (STs) for T. medium phylogroup (11 new), 15 STs for T. phagedenis phylogroup (9 new) and six T. pedis STs, of which two were new. This study shows that CODD stage 5 lesions still contain viable bacteria, representing all three known pathogenic Treponema spp. phylogroups, and these may thus play a role in disease transmission and epidemiology despite appearing healed after treatment. The high level CODD treponeme variability within an infected flock where sheep were bought from different sources, as might occur in common agricultural practice, may suggest reasons as to why the bacterial disease is difficult to treat, control and eradicate, and adds further complexity to the polybacterial pathogenesis of these lesions.

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

BACKGROUND

Treponeme-Associated Hoof Disease (TAHD) is a polybacterial, multifactorial disease affecting free-ranging wild elk (Cervus canadensis) in the Pacific Northwest. Previous studies have indicated a bacterial etiology similar to digital dermatitis in livestock, including isolation of Treponema species from lesions. The lesions appear to progress rapidly from ulcerative areas in the interdigital space or along the coronary band to severe, ulcerative, necrotic, proliferative lesions under-running the hoof wall, perforating the sole, and contributing to hoof elongation, deformity, and overgrowth. Eventually the lesions undermine the laminal structure leading to sloughing of the hoof horn capsule. The objective of this study was to characterize the bacterial communities associated with hoof lesions, which were categorized into 5 stages or disease grade severities, with 0 being unaffected tissue and 4 being sloughed hoof capsule. We also wanted to determine if the etiology of TAHD through morphological changes was dominated by Treponema, as observed in hoof diseases in livestock.

RESULTS

The bacterial 16S rRNA gene was sequenced from 66 hoof skin biopsy samples representing 5 lesion grades from samples collected by Washington Department of Fish and Wildlife as part of a voluntary hunter program. Analysis of the relative abundance of bacterial sequences showed that lesions were dominated by members of the bacterial phyla Proteobacteria, Firmicutes, Spirochaetes, Bacteroidetes and Actinobacteria. In lesion samples, members of the genus Treponema, Porphyromonas, and Mycoplasma increased with lesion severity. Association analysis indicated frequent identification of Treponema with Porphyromonas, Bacteroides and other anaerobic Gram-positive cocci.

CONCLUSIONS

The bacterial 16S rRNA gene sequencing confirmed the presence of Treponema species at all stages of TAHD lesions, treponeme specie-specific PCR and histopathology, indicating that the morphological changes are a continual progression of disease severity with similar bacterial communities. Association and abundance of these other pathogenic genera within lesions may mean synergistic role with Treponema in hoof disease pathogenesis. Characterizing bacteria involved in lesion development, and their persistence during disease progression, provides evidence for science-based management decisions in TAHD infected elk populations.

Molecular Diagnosis of Footrot and Contagious Ovine Digital Dermatitis in Small Ruminants in the Iberian Peninsula

Contagious ovine digital dermatitis (CODD) and footrot (FR), a sub-acute or acute necrotic (decaying) infectious disease involving the hoof and underlying tissues, pose economic challenges to herds in Spain and worldwide. The aetiological agent for FR is Dichelobacter nodosus, while CODD is caused by pathogenic Treponema phylogroups. We detail the findings derived from the analysis by qPCR of 105 pooled samples from 100 ovine and five caprine herds in Spain and Portugal, alongside 15 samples from healthy flocks in order to identify Dichelobacter nodosus, Fusobacterium necrophorum, Treponema spp., and three pathogenic Treponema phylogroups (T. phagedenis, T. medium, and T. pedis). Treponema spp. were detected in all 120 pools, including samples from the 15 healthy flocks where only one positive result for F. necrophorum was recorded. Mixed infections by agents different from Treponema spp. were identified in 68.57% of samples. Positive results for F. necrophorum and/or D. nodosus, were obtained for 91.4% of the pools, whereas the presence of the three pathogenic Treponema phylogroups was rare: each of them appeared in isolation in a single pool, while they were found in 18 pools in combination with other agents. While F. necrophorum was the sole finding in 16.2% of samples from affected herds, D. nodosus (the footrot causative agent) was only detected in 61% of affected farms. An improved qPCR protocol was implemented to determine the serogroups of D. nodosus in the samples and found all of them (except the G serogroup), often in combined infections (35.1%). This report concludes with comprehensive proposals for diagnosing, preventing, and treating hoof ailments, remarking the interest of the information about D. nodosus serogroups in order to improve the efficiency of immunization by choosing appropriate vaccine protocols.

Development of a multiplex quantitative PCR assay for simultaneous detection of Treponema phagedenis, Treponema pedis, Treponema medium, and 'Treponema vincentii' and evaluation on bovine digital dermatitis biopsies

Bovine digital dermatitis (BDD) is a contagious foot disease with worldwide occurrence in dairy cattle. The disease causes lameness and reduced animal welfare as well as economic losses for the farmer. The aetiology is not fully established but associations have been made with Treponema spp. Today, BDD diagnosis is mainly based on visual inspection of cattle feet, therefore this study aimed to develop a multiplex quantitative PCR (qPCR) assay targeting Treponema phagedenis, Treponema pedis, Treponema medium, and 'Treponema vincentii' to aid in diagnosis. The assay was tested for specificity on 53 bacterial strains and in silico on 168 Treponema spp. genomes, representative of at least 24 species. In addition, 37 BDD biopsies were analysed and the results compared to another qPCR assay published during the study period, which we modified by combining into a multiplex qPCR. The qPCR developed herein had a detection limit of 10 copies of each target species per PCR reaction. Both qPCR assays showed 100% specificity when tested on bacterial strains, but the qPCR developed in this study detected 3.4% more T. phagedenis-positive biopsies of lesion category M1-M4.1 than the modified assay. To conclude, the developed qPCR assay detecting T. phagedenis, T. pedis, T. medium, and 'T. vincentii' has high analytical sensitivity and specificity and provides a useful complementary tool for diagnosis and epidemiological studies of BDD. The assay could possibly also be used for contagious ovine digital dermatitis (CODD) as similar bacteriological profiles have been suggested for BDD and CODD, especially regarding certain Treponema spp.

Field Study on the Prevalence of Ovine Footrot, Contagious Ovine Digital Dermatitis, and Their Associated Bacterial Species in Swedish Sheep Flocks

Ovine footrot and contagious ovine digital dermatitis (CODD) cause lameness in sheep, affecting welfare and economics. Previous Swedish studies focused on individual slaughter lambs, leaving flock-wide prevalence less explored. This study examined the prevalence of footrot and CODD in Swedish sheep flocks, focusing on adult sheep. From 99 flocks, 297 swabs were analysed using real-time PCR for Dichelobacter nodosus, Fusobacterium necrophorum, and Treponema spp. Sampled feet were photographed and assessed using scoring systems for footrot and CODD. Results indicated footrot prevalences (footrot score ≥ 2) of 0.7% and 2.0% at the individual and flock levels, respectively, whereas there were no signs of CODD. The individual footrot prevalence was lower than that from a 2009 study but aligned with a 2020 study, both conducted on slaughter lambs. Dichelobacter nodosus, F. necrophorum, and Treponema spp. were found in 5.7%, 1.3%, and 65.0% of sheep, and in 9.1%, 3.0%, and 82.8% of flocks, respectively. Compared to the 2020 study, there was a notable decrease in F. necrophorum and Treponema spp., while D. nodosus was consistent. In conclusion, the findings show a low prevalence of footrot, CODD, D. nodosus, and F. necrophorum in Swedish sheep flocks. Continuous surveillance and owner education are important to maintain this favourable status.

A reduced potential for lameness bacterial transmission by Lucilia sericata larvae and flies through metamorphosis

Lameness in sheep is one of the most serious issues on farms in the UK and worldwide, affecting over 90% of all UK sheep flocks. Despite its severity and prevalence, there are knowledge gaps regarding transmission routes of bacterial pathogens associated with infectious lameness in sheep. As larvae of Lucilia sericata are commonly found on foot lesions on lame sheep, it was hypothesised that the flies or their larvae could harbour lameness associated bacteria. This study examined the gut contents of larvae obtained from the foot lesions of lame sheep and compared them to control larvae collected from infested cat food on the same farm. Of particular interest, were the presence of three different bacterial genera associated with lameness; Fusobacterium necrophorum, Dichelobacter nodosus and Treponema spp., for which viability was also investigated. Larvae were cultured In vitro and some allowed to metamorphose into flies before specific PCR assays were carried out on the gut contents. Results showed a significant association between the bacteria on the feet of the sheep and those within the larvae. Although the gut contents of all larvae found on sheep feet contained one or more of the lameness bacteria, none of the bacteria were recovered from the adult flies, suggesting a level of gut remodelling during metamorphosis. Interestingly, Treponema spp. and Fusobacterium spp. were viable when isolated from gut contents of larvae. Maintenance of infection from larvae to fly did not occur. However, it still remains important to control both disease and insect populations of farms to maintain animal welfare.

Comparison of clinical cure rates from footrot and contagious ovine digital dermatitis using zinc sulphate foot bathing and topical oxytetracycline: A randomised trial

BACKGROUND

This study reports the clinical cure rates of topical oxytetracycline and 10% zinc sulphate foot bathing for treatment of interdigital dermatitis (ID), footrot (FR) and contagious ovine digital dermatitis (CODD) in lambs.

METHODS

The study was a randomised controlled trial of 75 lambs. Group A (n = 38) was foot bathed daily for 5 days in 10% zinc sulphate for 15 minutes and group B was treated with daily topical oxytetracycline for 5 days. On days 0, 7, 14, 28 and 42, lambs were scored for locomotion and foot lesions were recorded.

RESULTS

The initial cure rates for ID were 96.20% and 97.00%; for FR, 100% and 95%; and for CODD, 90.09% and 83.33% for zinc sulphate and oxytetracycline, respectively. By day 42, these had changed to 53.16% and 61% for ID; 47.82% and 70% for FR; and 100% and 83.33% for CODD. There were no significant differences in cure rates between the treatments for most time points.

LIMITATIONS

The sample size was small, and further studies in larger cohorts and different classes of sheep are required before the findings can be translated into recommendations for clinical practice.

CONCLUSION

Both treatments achieved cure rates that are comparable to reported cure rates using systemic antibiotics and could be an effective alternative.

Evidence of novel Treponema phylotypes implicated in contagious ovine digital dermatitis and association of treponemes with major lameness causing foot pathogens

In this study 269 swabs collected from 254 ovine foot lesions and 15 apparently healthy ovine feet were screened by PCR for the presence of major lameness causing foot pathogens viz. Treponema species, D. nodosus, F. necrophorum and T. pyogenes with the presumption that ovine foot lesion positive for Treponema species alone or in association with other three pathogens were categorized as contagious ovine digital dermatitis (CODD). While samples positive for D. nodosus alone or its combination with F. necrophorum and T. pyogenes were considered as footrot (FR) and samples in which F. necrophorum or T. pyogenes was found either alone or in combination were considered as interdigital dermatitis (ID). The overall occurrence of Treponema sp. in ovine foot lesions was 48.0%, and ranged from 33 to 58%. In Treponema positive samples D. nodosus, F. necrophorum and T. pyogenes were present in 34 (27.4%), 66 (54.4%) and 84 (68.5%) in contrast to Treponema negative samples in which these were present in 15 (11.1%), 20 (14.12%) and 17 (12.6%) samples, respectively. The data signifies that Treponema sp. are significantly associated with these foot pathogens and their different combinations with Treponema sp. influence the severity of CODD lesion. The identification of Treponema phylotypes was done by sequencing the 16S rRNA gene fragment of ten representative samples. Out of ten sequences, four (Trep-2, Trep-4, Trep-7 and Trep-10) were identical to Treponema sp. phylotype 1 (PT1) that belongs to phylogroup T. refringens-like, one sequence (Trep-1) was genetically close (90% sequence homology) to Treponema brennaborense while five sequences (Trep-3, Trep-5, Trep-6, Trep-8 and Trep-9) matched with uncultured bacterium clones of treponemes forming separate monophyletic group in phylogenetic tree and could represent new digital dermatitis phylogroup presently containing five ovine specific phylotypes. This is the first report on the presence of Treponema phylotypes other than three digital dermatitis (DD) Treponema phylogroups viz. T. phagedenis-like, T. medium/T. vincentii-like, and T. pedis-like that are frequently detected in CODD lesions. Metagenomic analysis of two representative samples revealed the abundance of genus Treponema in CODD lesion while this genus was absent in swab collected from clinically healthy foot suggesting that it might play primary role in producing CODD. These findings may further aid in understanding the etiopathogenesis of CODD and could help to develop appropriate treatment and mitigation strategies to combat the disease.

A metagenomics approach to characterize the footrot microbiome in Merino sheep

In the Portuguese Alentejo region, Merino sheep breed is the most common breed, reared for the production of meat, dairy, and wool. Footrot is responsible for lameness, decreased animal welfare, and higher production losses, generating a negative economic impact. The disease is caused by Dichelobacter nodosus that interacts with the sheep foot microbiome, to date largely uncharacterized. In fact, Dichelobacter nodosus is not able to induce footrot by itself being required the presence of a second pathogen known as Fusobacterium necrophorum. To understand and characterize the footrot microbiome dynamics of different footrot lesion scores, a whole metagenome sequencing (WMGS) approach was used. Foot tissue samples were collected from 212 animals with different degrees of footrot lesion scores, ranging from 0 to 5. Distinct bacterial communities were associated with feet with different footrot scores identifying a total of 63 phyla and 504 families. As the severity of footrot infection increases the microorganisms' diversity decreases triggering a shift in the composition of the microbiome from a dominant gram-positive in mild stages to a dominant gram-negative in the severe stages. Several species previously associated with footrot and other polymicrobial diseases affecting the epidermis and provoking inflammatory responses such as Treponema spp., Staphylococcus spp., Streptococcus spp. and Campylobacter spp. were identified proliferating along with the lesions' severity. Although these bacteria are not able to initiate footrot, several evidences have been described supporting their association with the severity and incidence increase of footrot lesions caused by Dichelobacter nodosus and Fusobacterium necrophorum. Further investigation is required to establish the roles of particular taxa and identify which of them play a role in the disease process and which are opportunistic pathogens.

Detection and quantification of bacterial species DNA in bovine digital dermatitis lesions in swabs and fine-needle aspiration versus biopsies

Digital Dermatitis (DD) is a polymicrobial disease characterized by ulcerative lesions on the heel bulb of cattle and for which, despite being reported almost 50 years ago, information on the causative agent is still lacking. Tissue biopsies are regularly collected to identify bacterial presence-absence and their relative abundance in the microbiome, with sufficient evidence for the high abundance of species of Treponema spp. and other anaerobes in lesions. However, it is unclear what the potential of less-invasive sampling methods is for bacterial detection and quantification. This study aimed to test whether less-invasive sampling techniques, such as swabs and fine-needle aspiration (FNA), can be a convenient alternative to tissue biopsies in detecting and quantifying seven DD-associated bacteria in active, ulcerative DD lesions by qPCR. Twenty-two M2 DD lesions were collected using corresponding swabs, aspirates, and biopsies from dairy cows. Presence/absence and quantities of Treponema phagedenis, Treponema medium, Treponema pedis, Porphryromonas levii, Bacteroides pyogenes, Fusobacterium necrophorum, and Fusobacterium mortiferum were correlated, and Bland-Altman plot, McNemar's test, and Cohen's kappa coefficient were used to calculate the agreement among the methods. The quantities of all species were larger in swabs and smaller in aspirates compared to biopsies; however, the differences in bacterial enumeration observed between biopsies and swabs were smaller than in biopsies and aspirates. A strong correlation was observed between the quantity of T. pedis, T. medium, P. levii, and F. mortiferum in biopsies, swabs, and FNA. Yet, T. phagedenis presented the smallest difference between biopsies and swabs, followed by T. pedis and T. medium. In conclusion, swabs, aspirates, and biopsies were equal in their capacity to detect Treponema species based on the good agreement for bacteria presence/absence, with a more limited agreement for the other anaerobes, which were more often present in M2 lesions swabs by qPCR. Bacterial numbers were higher in swabs and lower in aspirates compared to biopsies, with the amounts of treponemes in swabs being closer to biopsies than in aspirates to biopsies. Therefore, aspirates were less suitable for bacterial quantification in DD lesions compared to the other methods.

SURVEILLANCE FOR AN EMERGENT HOOF DISEASE IN ELK (CERVUS ELAPHUS) IN THE US PACIFIC WEST SUPPLEMENTED BY 16S RRNA GENE AMPLICON SEQUENCING

A novel hoof disease of elk (Cervus elaphus) was described in southwestern Washington, US, in 2008 and was subsequently diagnosed in an adjacent area in northwestern Oregon in 2014. The disease, currently referred to as treponeme-associated hoof disease (TAHD), is characterized by lesions ranging from mild erosions, to severe ulcers with underrunning of the hoof capsule and heel-sole junction, to overgrown and avulsed hoof capsules. Histologically, lesions exhibit epithelial erosion or ulceration, suppurative inflammation, and the presence of argyrophilic spirochetes. We used data collected by the Washington Department of Fish and Wildlife and Oregon Department of Fish and Wildlife from 2008 to 2017 as reference for disease distribution. We then conducted enhanced surveillance in 2018-20 by obtaining 164 submissions from four US Pacific West states. We detected TAHD for the first time in Idaho and northern California, as well as in multiple counties in Washington and Oregon where it had not been previously reported. Given the unexpectedly broad disease distribution, continued surveillance is warranted to determine the full geographic extent of TAHD. From samples of 22 elk, we investigated 16S rRNA gene amplicon sequencing as a technique that could be used to supplement TAHD surveillance. Operational taxonomic units of the family Spirochaetaceae were identified in 10 of 12 histologically diagnosed TAHD-positive cases and two of 10 TAHD-negative cases. Phyla Spirochaetae (P<0.008), Fusobacteria (P<0.006), and Tenericutes (P<0.01) were overrepresented in samples from TAHD-positive feet when compared with TAHD-negative elk. A unique spirochete, PT19, was detected in hooves of 11 elk and from at least one elk in each state. Results support the use of 16S rRNA gene amplicon sequencing as a reliable and informative tool to supplement investigations into distribution and etiology of this presumed polybacterial disease.

An experimental model to induce digital dermatitis in beef calves

Background

Digital dermatitis (DD) is a multifactorial infectious disease affecting the skin on feet of cattle causing erosion and inflammation above the heel bulbs. Some cases of DD cause lameness and significantly impact animal welfare and productivity. While DD has emerged as a concern for the beef industry, key information regarding early detection and its impact on cattle behaviour is lacking. The primary objective of this study was to determine if an established DD experimental model for dairy calves could be used to induce DD lesions in beef calves. A secondary objective was to describe changes in behaviour and pain associated with induction of DD lesions. Eight beef calves acquired from a single cow-calf operator were enrolled in the study. Upon enrolment, calves were evaluated and determined to be free of foot lesions. Within the experimental environment, calves were housed in individual pens and assigned to two groups (mock-inoculated and inoculated). Both hind feet of each calf were enrolled. Within calf, inoculation protocol was consistent, and a 28-day experimental protocol was employed. Two days prior to inoculation, both hind feet of each calf were abraded (area above the heel bulbs and below the dewclaws), moistened, and wrapped to facilitate an anaerobic condition. Feet were inoculated with macerated DD lesion material or mock inoculum and remained wrapped until clinical signs of DD or protocol endpoint.

Results

After a period of 14 to 18 days post inoculation, three of five inoculated calves developed clinical signs (lameness), and upon close inspection, DD lesions were present on at least one hind foot. Two of five inoculated calves did not develop lesions within 28 days. Zero of three mock-inoculated calves developed DD. Treponema spp. were detected by quantitative polymerase chain reaction from biopsies of induced lesions. Measurements of behaviour prior to disease induction were numerically different between DD affected and mock-inoculated calves.

Conclusions

An experimental infection model established for dairy cattle was used to successfully induce acute DD lesions in three of five inoculated beef calves. This model can provide a framework to study intervention protocols and to evaluate the impact of DD on behaviour and pain.

Prevalence of bacterial species associated with ovine footrot and contagious ovine digital dermatitis in Swedish slaughter lambs

Background

Ovine footrot and contagious ovine digital dermatitis (CODD) are contagious mixed bacterial infections with major impacts on animal health and production. In Sweden, ovine footrot and CODD were first detected in 2004 and 2019, respectively. In 2009, a voluntary control programme for footrot was established, and a prevalence study in slaughter lambs was conducted, however, the distribution of footrot and CODD-associated bacteria is still unknown. This study examined the prevalence of Dichelobacter nodosus, Fusobacterium necrophorum and Treponema spp., as well as the current prevalence of footrot and CODD, in Swedish slaughter lambs.

Results

A total of 2048 feet, from 512 slaughter lambs, were collected from eight slaughterhouses throughout Sweden in autumn 2020. All feet were visually examined for lesions of footrot and CODD and sampled for subsequent real-time polymerase chain reaction (PCR) analysis. Nine lambs (1.8%) had at least one foot affected with footrot (footrot score ≥ 2). A CODD grade 1 lesion was detected in a single lamb (0.2%). The prevalence of D. nodosus, F. necrophorum and Treponema spp. was 6.1%, 7.6% and 90.6%, respectively. The D. nodosus detected were benign strains.

Conclusions

The prevalence of footrot in Swedish slaughter lambs has been significantly reduced, from 5.8 to 1.8%, during the past 11 years. This indicates that preventive measures, such as the national control programme and elimination of footrot from affected flocks, have been effective. A single lamb (0.2%) was found with a CODD lesion (grade 1). In Sweden, benign rather than virulent strains of D. nodosus seem to be the most common. Neither D. nodosus nor F. necrophorum were widespread among Swedish slaughter lambs, but both were more likely to be found in lambs with footrot. Treponema spp. was very commonly found in lambs with and without footrot, but there is a lack of information on the individual Treponema spp. present in Swedish slaughter lambs and their potential pathogenicity.

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

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.

Contagious Ovine Digital Dermatitis: A Novel Bacterial Etiology and Lesion Pathogenesis

Contagious ovine digital dermatitis (CODD) is a severe and common infectious foot disease of sheep and a significant animal welfare issue for the sheep industry in the UK and some European countries. The etiology and pathogenesis of the disease are incompletely understood. In this longitudinal, experimental study, CODD was induced in 18 sheep, and for the first time, the clinical lesion development and associated microbiological changes in CODD affected feet are described over time, resulting in a completely new understanding of the etiopathogenesis of CODD. The majority of CODD lesions (83.9%) arose from pre-existing interdigital dermatitis (ID) and/or footrot (FR) lesions. All stages of foot disease were associated with high levels of poly-bacterial colonization with five pathogens, which were detected by quantitative PCR (qPCR): Treponema medium, Treponema phagedenis, Treponema pedis, Dichelobacter nodosus, and Fusobacterium necrophorum. Temporal colonization patterns showed a trend for early colonization by T. phagedenis, followed by F. necrophorum and D. nodosus, T. medium, and then T. pedis, D. nodosus was present at significantly higher predicted mean log₁₀ genome copy numbers in FR lesions compared to both ID and CODD, while Treponema species were significantly higher in CODD and FR lesions compared to ID lesions (p < 0.001). Treatment of CODD-affected sheep with two doses of 10 mg/kg long acting amoxicillin resulted in a 91.7% clinical cure rate by 3 weeks post-treatment; however, a bacteriological cure was not established for all CODD-affected feet. The study found that in an infected flock, healthy feet, healed CODD feet, and treated CODD feet can be colonized by some or all of the five pathogens associated with CODD and therefore could be a source of continued infection in flocks. The study is an experimental study, and the findings require validation in field CODD cases. However, it does provide a new understanding of the etiopathogenesis of CODD and further supportive evidence for the importance of current advice on the control of CODD; namely, ensuring optimum flock control of footrot and prompt isolation and effective treatment of clinical cases.

A Trifecta of New Insights into Ovine Footrot for Infection Drivers, Immune Response, and Host-Pathogen Interactions

Footrot is a polymicrobial infectious disease in sheep causing severe lameness, leading to one of the industry's largest welfare problems. The complex etiology of footrot makes in situ or in vitro investigations difficult. Computational methods offer a solution to understanding the bacteria involved and how they may interact with the host, ultimately providing a way to identify targets for future hypothesis-driven investigative work. Here, we present the first combined global analysis of bacterial community transcripts together with the host immune response in healthy and diseased ovine feet during a natural polymicrobial infection state using metatranscriptomics. The intratissue and surface bacterial populations and the most abundant bacterial transcriptomes were analyzed, demonstrating that footrot-affected skin has reduced diversity and increased abundances of not only the causative bacterium Dichelobacter nodosus but also other species such as Mycoplasma fermentans and Porphyromonas asaccharolytica. Host transcriptomics reveals the suppression of biological processes related to skin barrier function, vascular functions, and immunosurveillance in unhealthy interdigital skin, supported by histological findings that type I collagen (associated with scar tissue formation) is significantly increased in footrot-affected interdigital skin compared to outwardly healthy skin. Finally, we provide some interesting indications of host and pathogen interactions associated with virulence genes and the host spliceosome, which could lead to the identification of future therapeutic targets.

First report on outbreaks of contagious ovine digital dermatitis in Sweden

BACKGROUND

Contagious ovine digital dermatitis (CODD) is considered widespread in the United Kingdom but was only recently reported in mainland Europe, as one outbreak in Germany. The disease can cause severe lameness in sheep and, if left untreated, can lead to total avulsion of the hoof capsule. CODD is considered to have multifactorial and polymicrobial aetiology, in which Treponema medium/Treponema vincentii phylogroup, Treponema phagedenis phylogroup and Treponema pedis are believed to play a significant role. Footrot and CODD have a close connection and footrot is considered an important risk factor for CODD.

CASE

Lameness, mainly in lambs aged 1.5 months, was reported on a farm in Sweden in spring 2018. The animals showed no signs of footrot and the causative agent, Dichelobacter nodosus, was not found. CODD was suspected but not confirmed, and the clinical signs subsided when the animals were turned out to pasture. In February 2019, young lambs and ewes were lame again and this time CODD was diagnosed. After treatment, the whole flock was slaughtered later in 2019 due to CODD. In autumn 2020, CODD was diagnosed on another Swedish farm, this time as part of a mixed infection with D. nodosus. The animals were treated with footbaths in zinc sulphate 10% by the farmer, but lameness recurred soon afterwards. The animals were treated, but ultimately the whole flock was slaughtered. No connection was found between the two farms.

CONCLUSION

The first two outbreaks of CODD in Sweden have been diagnosed and are described in this case report. If it spreads, CODD could have a negative impact on the Swedish sheep industry in terms of animal welfare, production and antibiotic use.