Association of unique, isolated treponemes with bovine digital dermatitis lesions

16S rRNA amplicon sequencing reveals a polymicrobial nature of complicated claw horn disruption lesions and interdigital phlegmon in dairy cattle

Lameness represents an intractable problem for the dairy industry. Complicated claw horn disruption lesions, interdigital hyperplasia, and interdigital phlegmon are important lameness causing foot lesions. Their aetiology is multifactorial, but infectious processes are likely implicated in disease pathogenesis. Our aim was to investigate the bacterial profiles of these lesions using 16S rRNA gene sequencing of samples obtained from 51 cattle across ten farms in the UK. In this study, interdigital hyperplasia, interdigital hyperplasia with signs of interdigital dermatitis, interdigital phlegmon, complicated sole ulcers, complicated toe ulcers lesions, and complicated white line lesions were investigated; corresponding healthy skin control samples were also analysed. All diseased tissues displayed reduced microbial richness and diversity (as described by Chao1, Shannon, and Simpson alpha-diversity indices) compared to their healthy skin control samples. Our results confirm the association of Treponema spp with some of these disorders. Other anaerobic bacteria including Fusobacterium spp., Fastidiosipila spp. and Porphyromonas spp. were implicated in the aetiology of all these lesions with the exception of interdigital hyperplasia. Complicated claw horn disruption lesions, and interdigital phlegmon were found to have similar bacterial profiles. Such sharing of bacterial genera suggests many of the infectious agents detected in these foot lesions are acting opportunistically; this finding could contribute towards future treatment and control strategies.

Treponeme-Associated Hoof Disease of Free-Ranging Elk ( Cervus elaphus) in Southwestern Washington State, USA

A novel foot disease in free-ranging elk ( Cervus elaphus) in southwestern Washington State emerged in 2008 and spread throughout the region. Initial studies showed adult elk had chronic hoof overgrowth, sole ulcers, and sloughed hoof capsules, but no cause was determined. To identify possible causes and characterize the earliest lesions, 9-, 7-, and 3-month-old elk were collected. Nine-month-old elk had sole ulcers (3/9 elk) and sloughed/overgrown hoof capsules (4/9 elk) similar to adults. Histologically, lesions consisted of coronary, heel bulb, and interdigital ulcers with suppurative inflammation, epithelial hyperplasia, deeply invasive spirochetes, and underrunning of the hoof capsule and heel-sole junction. Spirochetes were identified as Treponema via immunohistochemistry and polymerase chain reaction (PCR). Seven-month-old elk had similar underrunning foot ulcers (6/8 elk) with Treponema identified in all lesions but no chronic overgrowth or sloughed hoof capsules. Three-month-old calves had superficial coronary erosions with no inflammation or identifiable spirochetes (3/5 elk) but were culture/PCR positive for Treponema, suggesting possible early lesions. Lesions from 9- and 7-month-old elk included aerobic and anaerobic bacteria, many of which are associated with infectious foot disease in livestock. Antibody enzyme-linked immunosorbent assay of 7- and 3-month-old elk from the enzootic region showed a trend toward increased Treponema antibody titers compared to normal control elk from outside the region, further supporting the significance of Treponema in the pathogenesis of foot disease. Treponeme-associated hoof disease (TAHD) in elk, a debilitating and progressive condition, shares similarities to bovine digital dermatitis and contagious ovine digital dermatitis.

Isolation and identification of Treponema pedis and Treponema phagedenis-like organisms from bovine digital dermatitis lesions found in dairy cattle in Turkey

The isolation and identification of microorganisms associated with digital dermatitis (DD) in Turkish dairy cattle was investigated using punch skin biopsy samples from typical clinical lesions; they were collected from dairy farms and abattoirs in 5 different geographical locations in Turkey. Morphological characteristics and flagellation types were examined using a transmission electron microscope, and their enzyme profiles by enzyme activation kits; their catalase reaction characteristics were evaluated by the addition of 3% H₂O₂. Their phylogenies were identified using 16S rRNA and the results compared with known gene bank data. Bacterial cells were 5.0 to 18.2 µm long, 0.2 to 0.5 µm wide, and their minimum number of periplasmic flagellum was 4 (4:8:4) with a maximum of 8 (8:16:8). All isolates were catalase negative. Of the spirochetes isolated and identified, group I organisms showed close similarity with Treponema pedis (99% genetic homology), whereas those in group II were similar to Treponema phagedenis (98% homology). This is the first report of specific sub-groups of Treponema spp., isolated from Turkish dairy cattle presenting with DD lesions, being associated with this disease; these morphotypes were similar to those found globally in housed dairy cattle units and are probably significant microorganisms associated with the aetiopathogensis of this infectious disease causing acute bovine lameness. These results suggest that the distribution of DD-associated treponemes is not specific to particular geographic regions of Turkey.

Novel inflammatory cell infiltration scoring system to investigate healthy and footrot affected ovine interdigital skin

Ovine footrot is a degenerative disease of sheep feet leading to the separation of hoof-horn from the underlying skin and lameness. This study quantitatively examined histological features of the ovine interdigital skin as well as their relationship with pro-inflammatory cytokine (IL-1β) and virulent Dichelobacter nodosus in footrot. From 55 healthy and 30 footrot ovine feet, parallel biopsies (one fixed for histology) were collected post-slaughter and analysed for lesions and histopathological analysis using haematoxylin and eosin and Periodic Acid-Schiff. Histological lesions were similar in both conditions while inflammatory scores mirror IL-1β expression levels. Increased inflammatory score corresponded with high virulent D. nodosus load and was significant (p < 0.0001) in footrot feet with an inflammatory score of 3 compared to scores 1 and 2. In addition, in contrast to healthy tissues, localisation of eubacterial load extended beyond follicular depths in footrot samples. The novel inflammatory cell infiltration scoring system in this study may be used to grade inflammatory response in the ovine feet and demonstrated an association between severity of inflammatory response and increased virulent D. nodosus load.

A clinical and histopathological comparison of the effectiveness of salicylic acid to a compound of inorganic acids for the treatment of digital dermatitis in cattle

Bovine digital dermatitis (DD) is a painful infectious disease, causing lameness, reduced animal welfare, and production losses in dairy herds. The main factors contributing to DD are an infection with Treponema spp. and poor hygiene. Topical treatment has primarily consisted of antibiotics; however, the demand for effective nonantibiotic alternatives is increasing. The objective was to evaluate the performance of 3 nonantibiotic topical treatments (salicylic acid and a compound of inorganic acids in a 20% solution and in a dry form) on DD in a commercial dairy herd. Within the 30-d test period, 42 DD lesions on 33 Holstein cows were assigned to receive 1 of the 3 treatments. Lesions were biopsied before and after treatment and were clinically evaluated 5 times. Improved lesions were clinically defined as either healed (regeneration of the skin) or healing (dry lesions covered by a scab). Unhealed lesions were defined as either active [with a raw, moist, strawberry-like (granulating) surface] or mature (with a raised papillomatous appearance). The effectiveness of treatment was evaluated histopathologically using the following scores: 0 (no spirochetes present), 1 (small number of spirochetes present in the epidermis), 2 (moderate number of spirochetes present and reaching an intermediary level in the epidermis), and 3 (large number of spirochetes present and reaching the deepest part of the epidermis or the superficial dermis). The improvement rate was 10/14 (71%) for salicylic acid, 11/15 (73%) for the inorganic acid solution, and 8/13 (62%) for the inorganic acid powder. The analysis showed no difference among treatments. The association between clinical score and histopathological score was determined by an odds ratio. The odds ratio of a healed lesion having spirochetes in the epidermis was 0.58 and that of an active DD lesion having spirochetes in the epidermis was 26.5.

Clinical Perspectives of Digital Dermatitis in Dairy and Beef Cattle

Digital dermatitis is a polybacterial disease process of dairy and beef cattle. Lesions are most commonly identified on the plantar aspect of the interdigital cleft of the hind limbs. Treponema spp are routinely present in large numbers of active lesions. Lesions are painful to the touch and can result in clinical lameness. The infectious nature generally results in endemic infection of cattle herds and management requires a comprehensive and integrated multipronged approach. This article provides current perspectives regarding management and treatment of digital dermatitis on dairy and beef cattle operations and provides a review for clinicians dealing with a clinical outbreak.

Development of real-time PCR and loop-mediated isothermal amplification (LAMP) assays for the differential detection of digital dermatitis associated treponemes

Bovine digital dermatitis (DD) is a severe infectious cause of lameness in cattle worldwide, with important economic and welfare consequences. There are three treponeme phylogroups (T. pedis, T. phagedenis, and T. medium) that are implicated in playing an important causative role in DD. This study was conducted to develop real-time PCR and loop-mediated isothermal amplification (LAMP) assays for the detection and differentiation of the three treponeme phylogroups associated with DD. The real-time PCR treponeme phylogroup assays targeted the 16S-23S rDNA intergenic space (ITS) for T. pedis and T. phagedenis, and the flagellin gene (flaB2) for T. medium. The 3 treponeme phylogroup LAMP assays targeted the flagellin gene (flaB2) and the 16S rRNA was targeted for the Treponeme ssp. LAMP assay. The real-time PCR and LAMP assays correctly detected the target sequence of all control strains examined, and no cross-reactions were observed, representing 100% specificity. The limit of detection for each of the three treponeme phylogroup real-time PCR and LAMP assays was ≤ 70 fg/μl. The detection limit for the Treponema spp. LAMP assay ranged from 7-690 fg/μl depending on phylogroup. Treponemes were isolated from 40 DD lesion biopsies using an immunomagnetic separation culture method. The treponeme isolation samples were then subjected to the real-time PCR and LAMP assays for analysis. The treponeme phylogroup real-time PCR and LAMP assay results had 100% agreement, matching on all isolation samples. These results indicate that the developed assays are a sensitive and specific test for the detection and differentiation of the three main treponeme phylogroups implicated in DD.

Microbiota Analysis of an Environmental Slurry and Its Potential Role as a Reservoir of Bovine Digital Dermatitis Pathogens

At present, very little information exists regarding what role the environmental slurry may play as an infection reservoir and/or route of transmission for bovine digital dermatitis (DD), a disease which is a global problem in dairy herds. To investigate whether DD-related bacteria belong to the indigenous microbiota of the dairy herd environment, we used deep amplicon sequencing of the 16S rRNA gene in 135 slurry samples collected from different sites in 22 dairy farms, with and without DD-infected cows. Both the general bacterial populations and digital dermatitis-associated Treponema were targeted in this study. The results revealed significant differences in the bacterial communities between the herds, with only 12 bacterial taxa shared across at least 80% of all the individual samples. These differences in the herd microbiota appeared to reflect mainly between-herd variation. Not surprisingly, the slurry was dominated by ubiquitous gastrointestinal bacteria, such as Ruminococcaceae and Lachnospiraceae Despite the low relative abundance of spirochetes, which ranged from 0 to 0.6%, we were able to detect small amounts of bacterial DNA from DD-associated treponemes in the slurry. However, the DD-associated Treponema spp. were detected only in samples from herds with reported DD problems. These data indicate that treponemes involved in the pathogenesis of DD are not part of the normal environmental microflora in dairy herds without clinical DD and, consequently, that slurry is not a primary reservoir of infection.IMPORTANCE Bovine digital dermatitis (DD), a dermal disease which causes lameness in dairy cattle, is a serious problem worldwide. To control this disease, the infection reservoirs and transmission routes of DD pathogens need to be clarified. The dairy herd slurry may be a pathogen reservoir of DD-associated bacteria. The rationale for the present study was, therefore, to examine whether DD-associated bacteria are always present in slurry or if they are found only in DD-afflicted herds. The results strongly indicated that DD Treponema spp. are not part of the indigenous slurry and, therefore, do not comprise an infection reservoir in healthy herds. This study applied next-generation sequencing technology to decipher the microbial compositions of environmental slurry of dairy herds with and without digital dermatitis.

A novel approach to probe host-pathogen interactions of bovine digital dermatitis, a model of a complex polymicrobial infection

Background

Polymicrobial infections represent a great challenge for the clarification of disease etiology and the development of comprehensive diagnostic or therapeutic tools, particularly for fastidious and difficult-to-cultivate bacteria. Using bovine digital dermatitis (DD) as a disease model, we introduce a novel strategy to study the pathogenesis of complex infections.

Results

The strategy combines meta-transcriptomics with high-density peptide-microarray technology to screen for in vivo-expressed microbial genes and the host antibody response at the site of infection. Bacterial expression patterns supported the assumption that treponemes were the major DD pathogens but also indicated the active involvement of other phyla (primarily Bacteroidetes). Bacterial genes involved in chemotaxis, flagellar synthesis and protection against oxidative and acidic stress were among the major factors defining the disease.

Conclusions

The extraordinary diversity observed in bacterial expression, antigens and host antibody responses between individual cows pointed toward microbial variability as a hallmark of DD. Persistence of infection and DD reinfection in the same individual is common; thus, high microbial diversity may undermine the host’s capacity to mount an efficient immune response and maintain immunological memory towards DD. The common antigenic markers identified here using a high-density peptide microarray address this issue and may be useful for future preventive measures against DD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3341-7) contains supplementary material, which is available to authorized users.

Multilocus Sequence Typing of Pathogenic Treponemes Isolated from Cloven-Hoofed Animals and Comparison to Treponemes Isolated from Humans

Treponema species are implicated in many diseases of humans and animals. Digital dermatitis (DD) treponemes are reported to cause severe lesions in cattle, sheep, pigs, goats, and wild elk, causing substantial global animal welfare issues and economic losses. The fastidiousness of these spirochetes has previously precluded studies investigating within-phylogroup genetic diversity. An archive of treponemes that we isolated enabled multilocus sequence typing to quantify the diversity and population structure of DD treponemes. Isolates (n = 121) were obtained from different animal hosts in nine countries on three continents. The analyses herein of currently isolated DD treponemes at seven housekeeping gene loci confirm the classification of the three previously designated phylogroups: the Treponema medium, Treponema phagedenis, and Treponema pedis phylogroups. Sequence analysis of seven DD treponeme housekeeping genes revealed a generally low level of diversity among the strains within each phylogroup, removing the need for the previously used "-like" suffix. Surprisingly, all isolates within each phylogroup clustered together, regardless of host or geographic origin, suggesting that the same sequence types (STs) can infect different animals. Some STs were derived from multiple animals from the same farm, highlighting probable within-farm transmissions. Several STs infected multiple hosts from similar geographic regions, identifying probable frequent between-host transmissions. Interestingly, T. pedis appears to be evolving more quickly than the T. medium or T. phagedenis DD treponeme phylogroup, by forming two unique ST complexes. The lack of phylogenetic discrimination between treponemes isolated from different hosts or geographic regions substantially contrasts with the data for other clinically relevant spirochetes.

IMPORTANCE

The recent expansion of the host range of digital dermatitis (DD) treponemes from cattle to sheep, goats, pigs, and wild elk, coupled with the high level of 16S rRNA gene sequence similarity across hosts and with human treponemes, suggests that the same bacterial species can cause disease in multiple different hosts. This multilocus sequence typing (MLST) study further demonstrates that these bacteria isolated from different hosts are indeed very similar, raising the potential for cross-species transmission. The study also shows that infection spread occurs frequently, both locally and globally, suggesting transmission by routes other than animal-animal transmission alone. These results indicate that on-farm biosecurity is important for controlling disease spread in domesticated species. Continued surveillance and vigilance are important for ascertaining the evolution and tracking any further host range expansion of these important pathogens.

Severe Foot Lesions in Dairy Goats Associated with Digital Dermatitis Treponemes

Treponeme-associated foot disease has been described in cattle with digital dermatitis and sheep with contagious ovine digital dermatitis. In this study, severe foot lesions in dairy goats associated with digital dermatitis treponemes (i.e. Treponema medium, Treponema phagedenis and Treponema pedis) were characterized macroscopically, radiographically and histologically. The main macroscopic foot lesion was of extensive solar ulceration with or without exophytic papilliform hyperkeratosis. Radiographically, the distal phalanx and distal sesamoid bones were severely damaged and remodelled. Histologically, the lesion was categorized as a chronic lymphoplasmacytic, suppurative and ulcerative pododermatitis. Immunohistochemistry identified the spirochaetal microorganisms located extracellularly in the superficial horn. Study limitations mean that the treponeme bacteria could not be considered the sole or causal agents in the cases described.

A Highly Effective Protocol for the Rapid and Consistent Induction of Digital Dermatitis in Holstein Calves

Bovine Digital Dermatitis (DD) is a leading cause of lameness in dairy cattle. DD is reportedly increasing in prevalence in beef cattle feedlots of the US. The exact etiologic agent(s) responsible for the disease have yet to be determined. Multiple studies have demonstrated the presence of a variety of Treponema spp. within lesions. Attempts to reproduce clinically relevant disease using pure cultures of these organisms has failed to result in lesions that mirror the morphology and severity of naturally occurring lesions. This manuscript details the systematic development of an experimental protocol that reliably induces digital dermatitis lesions on a large enough scale to allow experimental evaluation of treatment and prevention measures. In total, 21 protocols from five experiments were evaluated on their effectiveness in inducing DD lesions in 126 Holstein calves (504 feet). The protocols varied in the type and concentration of inoculum, frequency of inoculation, duration the feet were wrapped, and type of experimental controls need to validate a successful induction. Knowledge gained in the first four experiments resulted in a final protocol capable of inducing DD lesions in 42 of 44 (95%) feet over a 28 day period. All induced lesions were macroscopically and microscopically identified as clinical DD lesions by individuals blinded to protocols. Lesions were also located at the site of inoculation in the palmer aspect of the interdigital space, and induced clinically measurable lameness in a significant portion of the calves. Collectively these results validate the model and provide a rapid and reliable means of inducing DD in large groups of calves.

Potential bacterial core species associated with digital dermatitis in cattle herds identified by molecular profiling of interdigital skin samples

Although treponemes are consistently identified in tissue from bovine digital dermatitis (DD) lesions, the definitive etiology of this debilitating polymicrobial disease is still unresolved. To study the microbiomes of 27 DD-infected and 10 healthy interdigital skin samples, we used a combination of different molecular methods. Deep sequencing of the 16S rRNA gene variable regions V1-V2 showed that Treponema, Mycoplasma, Fusobacterium and Porphyromonas were the genera best differentiating the DD samples from the controls. Additional deep sequencing analysis of the most abundant genus, Treponema, targeting another variable region of the 16S rRNA gene, V3-V4, identified 15 different phylotypes, among which Treponema phagedenis-like and Treponema refringens-like species were the most abundant. Although the presence of Treponema spp., Fusobacterium necrophorum and Porphyromonas levii was confirmed by fluorescence in situ hybridization (FISH), the results for Mycoplasma spp. were inconclusive. Extensive treponemal epidermal infiltration, constituting more than 90% of the total bacterial population, was observed in 24 of the 27 DD samples. F. necrophorum and P. levii were superficially located in the epidermal lesions and were present in only a subset of samples. RT-qPCR analysis showed that treponemes were also actively expressing a panel of virulence factors at the site of infection. Our results further support the hypothesis that species belonging to the genus Treponema are major pathogens of DD and also provide sufficient clues to motivate additional research into the role of M. fermentans, F. necrophorum and P. levii in the etiology of DD.

Isolation of digital dermatitis treponemes from cattle hock skin lesions

BACKGROUND

Bovine hock lesions present a serious welfare and production issue on dairy farms worldwide. Current theories suggest that trauma is an important factor in the formation of hock lesions, although infection may also play a role in increasing their severity and duration.

HYPOTHESIS

Digital dermatitis (DD) lesions in dairy cows are strongly associated with specific treponeme bacteria which are opportunistic invaders of other skin regions. Hock lesions were tested to ascertain if they too contained treponemes.

ANIMALS

Swab and tissue samples were taken from hock lesions from two farms in South West England.

METHODS

Hock lesions were classified into two categories: open lesions, which were often bleeding and ulcerated, or were encrusted; and closed lesions, which were classified as hair loss with no skin breakage. PCR assays and bacterial isolation were used to detect treponemes in hock lesions.

RESULTS

All three phylogroups of digital dermatitis treponemes were detectable and isolated from open hock lesions only, with closed lesions showing no evidence of treponeme infection, either by PCR or bacterial culture. When analysed by 16S rRNA gene sequencing, the cultured treponeme DNA showed complete homology or was very similar to that found in foot lesions. Additionally, skin swabs from near the open hock wounds were also positive by PCR assay and isolation for the DD treponemes.

CONCLUSIONS AND CLINICAL IMPORTANCE

Identification of the contribution of these infectious agents will allow for more optimal treatments to be developed that reduce the prevalence and healing times of both hock and DD lesions.

Histopathological Characterization of the Lesions of Contagious Ovine Digital Dermatitis and Immunolabelling of Treponema-like Organisms

Contagious ovine digital dermatitis (CODD) is a cause of severe lameness in sheep and the three Treponema phylogroups Treponema medium/Treponema vincentii-like, Treponema phagedenis-like and Treponema pedis have been associated with clinical disease. The aims of this study were: (1) to describe the histopathological changes associated with each previously established grade of clinical lesion, and (2) to investigate immunohistochemically the association of the Treponema-like organisms with the observed histopathological changes. Early lesions were characterized by lymphoplasmacytic infiltration of the distal digital skin, with suppurative coronitis and intracorneal pustules. In more advanced stages of the disease there was complete separation of the dorsal wall of the hoof with a necrotizing and fibrinosuppurative exudate and dermatitis. The later lesions were mostly resolved, but with milder suppurative changes remaining within the cornified layer and periosteal reaction of the dorsal aspect of the distal phalanx. Large numbers of Treponema-like organisms were identified within early grade lesions (as well as later, more advanced grade lesions) and were specifically associated with the observed histopathological changes. The results of this study provide some evidence in support of the hypothesis that the three CODD-associated Treponema phylogroups are involved in the aetiopathogenesis of this disease.

Digital Dermatitis in Cattle: Current Bacterial and Immunological Findings

Globally; digital dermatitis is a leading form of lameness observed in production dairy cattle. While the precise etiology remains to be determined; the disease is clearly associated with infection by numerous species of treponemes; in addition to other anaerobic bacteria. The goal of this review article is to provide an overview of the current literature; focusing on discussion of the polybacterial nature of the digital dermatitis disease complex and host immune response. Several phylotypes of treponemes have been identified; some of which correlate with location in the lesion and some with stages of lesion development. Local innate immune responses may contribute to the proliferative, inflammatory conditions that perpetuate digital dermatitis lesions. While serum antibody is produced to bacterial antigens in the lesions, little is known about cellular-based immunity. Studies are still required to delineate the pathogenic traits of treponemes associated with digital dermatitis; and other host factors that mediate pathology and protection of digital dermatitis lesions.

Bovine digital dermatitis: Current concepts from laboratory to farm

Bovine digital dermatitis (DD) is a severe infectious disease causing lameness in dairy cattle worldwide and is an important ruminant welfare problem that has considerable economic issues. Bovine DD is endemic in many regions worldwide and it is important to understand this major disease so that effective control strategies can be identified. There is substantial evidence that specific treponeme phylotypes play an important causative role in bovine DD. This review considers current research, including DD Treponema spp. investigations, associated DD pathobiology, and current and potential treatment and control options. Epidemiological data, alongside new microbiological data, help delineate important transmission routes and reservoirs of infection that allow effective interventions to be identified. Better on-farm housing hygiene, pasture access, routine footbathing and claw trimming with disinfected equipment need to be implemented to significantly reduce the incidence of DD. There is a paucity of peer reviewed research into both commonly used and novel treatments. In vitro antimicrobial susceptibility studies of DD treponemes and effective treatment of human treponematoses clearly indicate that antibiotics frequently selected for DD treatments are not the most efficacious. Whilst there are understandable concerns over milk withdrawal times in dairy cattle, more needs to be done to identify, license and implement more appropriate antibiotic treatments, since continued overuse of less efficacious antibiotics, applied incorrectly, will lead to increased disease recurrence and transmission. More research is needed into methods of preventing DD that circumvent the use of antibiotics, including vaccination and transmission blocking studies, to reduce or hopefully eradicate DD in the future.

Draft genome sequence of 'Treponema phagedenis' strain V1, isolated from bovine digital dermatitis

‘Treponema phagedenis’ is considered to be a key agent in the pathogenesis of bovine digital dermatitis, an infectious foot condition of economic and animal welfare importance. We hereby report the draft sequence of ‘T. phagedenis’ strain V1. The draft genome assembly consists of 51 scaffolds comprising 3,129,551 bp and a GC-content of 39.9 %. Putative pathogenicity related factors have been identified in the genome that can be used in future studies to gain insight into the pathogenic mechanisms of ‘T. phagedenis’.

The gastrointestinal tract as a potential infection reservoir of digital dermatitis-associated treponemes in beef cattle and sheep

Digital dermatitis (DD) is an important cause of lameness in dairy cattle worldwide. It has now been reported in beef cattle and also sheep (contagious ovine digital dermatitis [CODD]). Three Treponema phylogroups are consistently isolated from lesions, Treponema medium-like, Treponema phagedenis-like, and Treponema pedis. The gastrointestinal (GI) tract and feces are suggested sites of treponemal infection in dairy cattle; however, isolation of DD-associated treponemes from these areas has previously failed. This study surveyed gingival tissues, rectal tissues, and feces of beef cattle and sheep for the molecular presence (PCR) and isolation of the three cultivable DD-treponeme phylogroups. Of the sheep gingival (n = 40) and rectal (n = 40) tissues, 1/40 gingival tissues was positive for DD-associated treponemes (T. pedis), as were 3/40 rectal tissues (one containing T. medium-like and two containing T. pedis). No DD-associated treponeme DNA was amplified from beef cattle rectal tissues (n = 40); however, 4/40 beef gingival tissues were positive for DD-associated treponemes (all containing T. phagedenis-like). A T. phagedenis-like DD-associated treponeme was isolated from the rectal tissue of a CODD symptomatic sheep. Beef cattle (n = 41) and sheep (n = 79) feces failed to amplify DD-associated Treponema DNA. Twenty-two treponemes were isolated from sheep feces; however, upon phylogenetic analysis, these clustered with the considered nonpathogenic treponemes. This study detected DD-associated treponemes in the GI tract tissues of sheep and beef cattle and successfully isolated a DD-associated treponeme from ruminant rectal tissue. This gives evidence that the GI tract is an important infection reservoir of DD-associated treponemes in multiple DD-infected species.

Digital Dermatitis in Dairy Cows: A Review of Risk Factors and Potential Sources of Between-Animal Variation in Susceptibility

Simple Summary

Dairy cow lameness is a major problem for the industry, causing reduced animal welfare and economic loss. Digital dermatitis (DD) is a bacterial disease causing painful lesions, generally on the heels of the rear feet, and is an important cause of lameness. There appears to be individual variation between animals in susceptibility to this disease. Particular physical, physiological and behavioural factors might influence individual susceptibility, but further work is required to clarify the influence of these factors and to determine how this information could be used to develop breeding and management strategies to reduce DD prevalence.

Abstract

Digital dermatitis (DD) is a bacterial disease that primarily affects the skin on the heels of cattle. It is a major cause of lameness in dairy cows and a significant problem for the dairy industry in many countries, causing reduced animal welfare and economic loss. A wide range of infection levels has been found on infected farms, prompting investigations into both farm level and animal level risk factors for DD occurrence. There also appears to be individual variation between animals in susceptibility to the disease. The identification of factors affecting individual variation in susceptibility to DD might allow changes in breeding policies or herd management which could be used to reduce DD prevalence. Factors mentioned in the literature as possibly influencing individual variation in susceptibility to DD include physical factors such as hoof conformation and properties of the skin, physiological factors such as the efficacy of the immune response, and behavioural factors such as standing half in cubicles. Further work is required to determine the influence of these factors, identify the genetic basis of variation, clarify the level of heritability of DD susceptibility and to determine how this is correlated with production and health traits currently used in breeding programmes.

The etiology of digital dermatitis in ruminants: recent perspectives

Digital dermatitis (DD) is a multifactorial polymicrobial infectious disease originally described in dairy cattle, but is increasingly recognized in beef cattle, sheep, and more recently, elk and goats. Clinical bovine lesions typically appear on the plantar surface of the hind foot from the interdigital space and heel bulb to the accessory digits, with a predilection for skin–horn junctions. Lesions present as a painful ulcerative acute or chronic inflammatory process with differing degrees of severity. This variability reflects disease progression and results in a number of different clinical descriptions with overlapping pathologies that ultimately have a related bacterial etiology. The goal of this review article is to provide a concise overview of our current understanding on digital dermatitis disease to facilitate clinical recognition, our current understanding on the causative agents, and recent advances in our understanding of disease transmission.

A molecular epidemiology of treponemes in beef cattle digital dermatitis lesions and comparative analyses with sheep contagious ovine digital dermatitis and dairy cattle digital dermatitis lesions

Bovine digital dermatitis (BDD) is an infective foot disease commonly reported in dairy cattle where Treponema are considered as the primary causative infectious agents. There still remains little definitive information on the etiology of BDD in beef cattle suggesting further investigations are warranted. Beef BDD lesions (n=34) and healthy beef foot tissues (n=38) were analysed by PCR for three BDD-associated Treponema phylogroups and also for Dichelobacter nodosus and Fusobacterium necrophorum. Spirochete culture was attempted on all BDD lesion samples. One or more BDD-associated Treponema phylogroups were detected in 100% of beef BDD lesions. "Treponema medium/Treponema vincentii-like", "Treponema phagedenis-like" and Treponema pedis spirochetes were identified in 27/34 (79%), 31/34 (91%) and 24/34 (71%) of BDD lesions, respectively. No BDD-associated treponeme DNA was amplified from beef healthy foot tissues. D. nodosus and F. necrophorum were present in 24/34 (71%) and 15/34 (44%) of lesions and 10/38 (26%) and 12/38 (32%) of healthy foot tissues, respectively. Twenty spirochetes were isolated from beef BDD lesions; 19 were representatives of the three BDD-associated Treponema phylogroups. One spirochete isolate shared less than 97% 16S rRNA gene similarity to the three cultivable BDD-associated Treponema phylogroups and therefore may represent a novel taxa of Treponema. Upon comparison, sheep contagious ovine digital dermatitis (CODD), dairy cattle and beef cattle BDD lesions appear to have extremely similar bacteriological data and therefore provides evidence of a shared etiopathogenesis posing concerns for cross-species transmission.

Treponemes detected in digital dermatitis lesions in Brazilian dairy cattle and possible host reservoirs of infection

The main pathogenic treponemes causing bovine digital dermatitis were identified from 17 infected herds in southern Brazil for the first time in this study using PCR. We did not find a relationship between treponeme phylogroup composition and clinical classification. Treponema phagedenis was present in all lesions. Rumen fluid was implicated as a reservoir location for these pathogens.

Altered microbiomes in bovine digital dermatitis lesions, and the gut as a pathogen reservoir

Bovine digital dermatitis (DD) is the most important infectious disease associated with lameness in cattle worldwide. Since the disease was first described in 1974, a series of Treponema species concurrent with other microbes have been identified in DD lesions, suggesting a polymicrobial etiology. However, the pathogenesis of DD and the source of the causative microbes remain unclear. Here we characterized the microbiomes of healthy skin and skin lesions in dairy cows affected with different stages of DD and investigated the gut microbiome as a potential reservoir for microbes associated with this disease. Discriminant analysis revealed that the microbiomes of healthy skin, active DD lesions (ulcerative and chronic ulcerative) and inactive DD lesions (healing and chronic proliferative) are completely distinct. Treponema denticola, Treponema maltophilum, Treponema medium, Treponema putidum, Treponema phagedenis and Treponema paraluiscuniculi were all found to be present in greater relative abundance in active DD lesions when compared with healthy skin and inactive DD lesions, and these same Treponema species were nearly ubiquitously present in rumen and fecal microbiomes. The relative abundance of Candidatus Amoebophilus asiaticus, a bacterium not previously reported in DD lesions, was increased in both active and inactive lesions when compared with healthy skin. In conclusion, our data support the concept that DD is a polymicrobial disease, with active DD lesions having a markedly distinct microbiome dominated by T. denticola, T. maltophilum, T. medium, T. putidum, T. phagedenis and T. paraluiscuniculi. Furthermore, these Treponema species are nearly ubiquitously found in rumen and fecal microbiomes, suggesting that the gut is an important reservoir of microbes involved in DD pathogenesis. Additionally, the bacterium Candidatus Amoebophilus asiaticus was highly abundant in active and inactive DD lesions.

High-level association of bovine digital dermatitis Treponema spp. with contagious ovine digital dermatitis lesions and presence of Fusobacterium necrophorum and Dichelobacter nodosus

Contagious ovine digital dermatitis (CODD) is an important foot disease in sheep, with significant animal welfare and economic implications. It is thought that CODD emerged from bovine digital dermatitis (BDD) via treponemal bacteria. With wildlife species such as elk now suffering a CODD-like disease, it is imperative to clarify these disease etiologies. A large investigation into treponemal association with CODD is warranted. CODD lesions (n = 58) and healthy sheep foot tissues (n = 56) were analyzed by PCR for the three BDD-associated Treponema phylogroups and two other lameness-associated bacteria, Dichelobacter nodosus and Fusobacterium necrophorum. Spirochete culture was also attempted on CODD lesions. "Treponema medium/Treponema vincentii-like," "Treponema phagedenis-like," and Treponema pedis spirochetes were identified in 39/58 (67%), 49/58 (85%), and 41/58 (71%) of CODD lesions, respectively. One or more BDD-associated Treponema phylogroups were detected in 100% of CODD lesions. Healthy foot tissues did not amplify BDD-associated Treponema phylogroup DNA. D. nodosus and F. necrophorum were present in 34/58 (59%) and 41/58 (71%) of CODD lesions and 22/56 (39%) and 5/56 (9%) of healthy foot tissues, respectively. Thirty-two spirochetes were isolated from CODD lesions, with representatives clustering with, and indistinguishable from, each of the three BDD-associated Treponema phylogroups based on 16S rRNA gene comparisons. This study for the first time demonstrates a high-level association for BDD treponeme phylogroups in CODD and their absence from healthy tissues, supporting the hypothesis that BDD treponemes play a primary causative role in CODD and confirming that the specific PCR assays are an effective differential diagnostic tool for CODD.

Digital dermatitis treponemes associated with a severe foot disease in dairy goats

A UK dairy goat herd was assessed after reports of a severe lameness problem of unknown aetiology. A lameness prevalence estimate was produced and individual clinical examination of 15 randomly selected lame goats was performed. Fifteen animals had foot lesions closely resembling contagious ovine digital dermatitis (CODD) in sheep. Eight of the goats examined presented with typical CODD lesions and seven showed what appeared to be a more severe CODD with under-running of the sole. Ten biopsy samples were obtained from the foot lesions and tested by PCR for the three previously isolated digital dermatitis (DD) Treponema phylogroups and culture of treponemes was attempted. Ninety per cent of the biopsy samples were positive for Treponema medium/Treponema vincentii-like spirochaetes and Treponema phagedenis-like DD spirochaetes and 80per cent were positive for Treponema pedis. Spirochaetes were successfully isolated from 50 per cent of lesion samples. Three isolates were identified as belonging to the T. phagedenis-like spirochaetes and two were identified as T. pedis. The frequent isolation of similar treponemes to those isolated from bovine digital dermatitis and CODD lesions and the identification of these DD-associated phylotypes in the vast majority of lesions support the hypothesis that this novel foot condition is associated with infection by DD treponemes, and given the similarities to CODD, it suggests a causal role.

Isolation of digital dermatitis treponemes from hoof lesions in Wild North American Elk (Cervus elaphus) in Washington State, USA

Since 2008, a large increase in the numbers of cases of lameness have been seen in wild North American elk (Cervus elaphus) from Washington State, USA. The most recent cases manifested as foot lesions similar both clinically and pathologically to those seen in digital dermatitis (DD) in cattle and sheep, a disease with a bacterial etiopathogenesis. To determine whether the same bacteria considered responsible for DD are associated with elk lameness, lesion samples were subjected to bacterial isolation studies and PCR assays for three phylogroups of relevant DD treponemes. The DD treponemes were isolated from lesional tissues but not from control feet or other areas of the diseased foot (including the coronary band or interdigital space), suggesting that the bacteria are strongly associated with DD lesions and may therefore be causal. In addition, PCR analysis revealed that all three unique DD treponeme phylotypes were found in elk hoof disease, and in 23% of samples, all 3 DD-associated treponemes were present in lesions. Sequence analysis of the 16S rRNA gene showed that the elk lesion treponemes were phylogenetically almost identical to those isolated from cattle and sheep DD lesions. The isolates were particularly similar to two of the three culturable DD treponeme phylotypes: specifically, the Treponema medium/Treponema vincentii-like and Treponema phagedenis-like DD spirochetes. The third treponeme culturable phylogroup (Treponema pedis), although detected by PCR, was not isolated. This is the first report describing isolation of DD treponemes from a wildlife host, suggesting that the disease may be evolving to include a wider spectrum of cloven-hoofed animals.

Immune response against Treponema spp. and ELISA detection of digital dermatitis

The objective of this longitudinal study was to evaluate the immune response against Treponema spp. infection in dairy heifers affected with digital dermatitis (DD). In addition, the accuracy of an indirect ELISA detecting anti-Treponema IgG antibodies in identifying clinical DD status has been assessed. A cohort of 688 pregnant Holstein heifers was evaluated at least 3 times before calving during a period of 6 mo. Complete clinical assessment of DD presence on the back feet of each heifer and blood extraction were performed in a stand-up chute. Digital dermatitis cases were characterized by the M-stage classification system and size and level of skin proliferation. An ELISA was performed on blood serum samples obtained from a subcohort of 130 heifers. For description purposes, the animals were classified by the number of clinical cases experienced during the study period as type I (no clinical cases were observed), type II (only 1 acute clinical case diagnosed), and type III (at least 2 acute clinical cases diagnosed). Multivariable repeated-measures models were used to evaluate the immune response against Treponema spp. infection. A binormal Bayesian model for the ELISA data without cut-point values was used to assess the accuracy of the ELISA as a diagnostic tool. Animals that never experienced a DD event throughout the study kept a constant low level of antibody titer. A 56% increase in mean ELISA titer was observed in heifers upon a first clinical DD case diagnosis. After topical treatment of an acute DD case with oxytetracycline, the antibody titer decreased progressively in type II heifers, achieving mean levels of those observed in healthy cows after a mean of 223 d. Surprisingly, antibody titer was not increased in the presence of M1 (DD lesion <20mm in diameter surrounded by healthy skin) and M4.1 (DD lesion <20mm in diameter embedded in a circumscribed dyskeratotic or proliferative skin alteration) DD stages. Type III cows showed a slight increase in antibody levels. The presence of skin proliferation at first DD diagnosis was found to be associated with an odds ratio of 2.04 of becoming a type III heifer in relation to heifers presenting first lesions without skin proliferation. The ELISA validity was estimated by an area under the curve of 0.88. Predicted probabilities of infection are provided for a range of ELISA values and prevalence of infection. Early detection and treatment is essential to control DD and the ELISA can be used in understanding the immunopathology of DD and shows great promise for prescreening purposes during DD management programs in combination with traditional clinical inspection.

Deep sequencing analysis reveals temporal microbiota changes associated with development of bovine digital dermatitis

Bovine digital dermatitis (DD) is a leading cause of lameness in dairy cattle throughout the world. Despite 35 years of research, the definitive etiologic agent associated with the disease process is still unknown. Previous studies have demonstrated that multiple bacterial species are associated with lesions, with spirochetes being the most reliably identified organism. This study details the deep sequencing-based metagenomic evaluation of 48 staged DD biopsy specimens collected during a 3-year longitudinal study of disease progression. Over 175 million sequences were evaluated by utilizing both shotgun and 16S metagenomic techniques. Based on the shotgun sequencing results, there was no evidence of a fungal or DNA viral etiology. The bacterial microbiota of biopsy specimens progresses through a systematic series of changes that correlate with the novel morphological lesion scoring system developed as part of this project. This scoring system was validated, as the microbiota of each stage was statistically significantly different from those of other stages (P < 0.001). The microbiota of control biopsy specimens were the most diverse and became less diverse as lesions developed. Although Treponema spp. predominated in the advanced lesions, they were in relatively low abundance in the newly described early lesions that are associated with the initiation of the disease process. The consortium of Treponema spp. identified at the onset of disease changes considerably as the lesions progress through the morphological stages identified. The results of this study support the hypothesis that DD is a polybacterial disease process and provide unique insights into the temporal changes in bacterial populations throughout lesion development.

Differential inflammatory responses of bovine foot skin fibroblasts and keratinocytes to digital dermatitis treponemes

Bovine digital dermatitis (BDD) is a serious infectious inflammatory lameness causing pain and suffering to many cattle worldwide and which has severe economic implications. This study set out to investigate relationships between the treponemes considered causal of BDD and the local inflammatory response of the bovine host. Here we describe, for the first time, the isolation of bovine foot skin keratinocytes and fibroblasts as separate cell lineages. These cell lines were then exposed to treponeme whole-cell sonicates, and the gene expression of selected host inflammatory mediators investigated using quantitative reverse transcriptase PCR. Several genes, including those encoding RANTES/CCL5, MMP12, TNFα, TGFβ and TIMP3 were significantly upregulated in fibroblasts exposed to whole-cell sonicates derived from BDD treponeme phylotypes. For each of the above genes there were similar fibroblast expression increases for all three BDD treponeme phylotypes tested, suggesting common virulence mechanisms. With bovine foot skin keratinocytes, we were unable to detect expression of RANTES/CCL5 and after incubation with BDD treponeme constituents we were unable to observe any significant changes in expression of inflammatory mediators tested. These contrasting results suggest fibroblasts rather than keratinocytes may be an important shared target of pathogenesis for BDD treponemes.

Presence of digital dermatitis treponemes on cattle and sheep hoof trimming equipment

Digital dermatitis (DD) is an infectious foot disease causing severe lameness in dairy cattle (worldwide) and sheep (UK). This study investigated whether DD Treponema phylogroups can be present on equipment used to trim ruminant hooves and, therefore, consider this trimming equipment as a possible vector for the transmission of DD. Equipment was tested after being used to trim DD symptomatic and asymptomatic cattle and sheep hooves, and subsequently after disinfection of equipment. After trimming, 'Treponema medium/Treponema vincentii-like', 'Treponema phagedenis-like' and 'Treponema denticola/T putidum-like' DD spirochaetes, were shown to be present on 23/37 (62%), 21/37 (57%) and 20/37 (54%) of knives, respectively. After disinfection, detection rates for the DD treponemes were 9/37 (24%), 6/37 (16%) and 3/37 (8%), respectively. Following culture of a swab, an isolate belonging to the T phagedenis-like spirochaetes was identified from a knife sample after trimming a DD positive cow. No isolates were obtained from knife samples after disinfection. This new data has, for the first time, identified treponemes in the farm environment, and highlighted disinfection of hoof trimming equipment between animals and between farms, as a logical precaution to limit the spread of DD.

Discovery of bovine digital dermatitis-associated Treponema spp. in the dairy herd environment by a targeted deep-sequencing approach

The bacteria associated with the infectious claw disease bovine digital dermatitis (DD) are spirochetes of the genus Treponema; however, their environmental reservoir remains unknown. To our knowledge, the current study is the first report of the discovery and phylogenetic characterization of rRNA gene sequences from DD-associated treponemes in the dairy herd environment. Although the spread of DD appears to be facilitated by wet floors covered with slurry, no DD-associated treponemes have been isolated from this environment previously. Consequently, there is a lack of knowledge about the spread of this disease among cows within a herd as well as between herds. To address the issue of DD infection reservoirs, we searched for evidence of DD-associated treponemes in fresh feces, in slurry, and in hoof lesions by deep sequencing of the V3 and V4 hypervariable regions of the 16S rRNA gene coupled with identification at the operational-taxonomic-unit level. Using treponeme-specific primers in this high-throughput approach, we identified small amounts of DNA (on average 0.6% of the total amount of sequence reads) from DD-associated treponemes in 43 of 64 samples from slurry and cow feces collected from six geographically dispersed dairy herds. Species belonging to the Treponema denticola/Treponema pedis-like and Treponema phagedenis-like phylogenetic clusters were among the most prevalent treponemes in both the dairy herd environment and the DD lesions. By the high-throughput approach presented here, we have demonstrated that cow feces and environmental slurry are possible reservoirs of DD-associated treponemes. This method should enable further clarification of the etiopathogenesis of DD.

Severe hoof disease in free-ranging Roosevelt elk (Cervus elaphus roosevelti) in southwestern Washington, USA

Reports of free-ranging Roosevelt elk (Cervus elaphus roosevelti) with abnormal hooves and lameness increased significantly in southwestern Washington, USA, during winter 2008. In March 2009 we examined five severely affected elk with clinical lameness from this region to characterize hoof lesions, examine the general health of affected elk, and potentially identify etiologies causing hoof disease. Three clinically normal elk from an adjacent but unaffected region were also collected as normal controls. Grossly, affected elk had deformed hooves that were asymmetrical, markedly elongated, and curved or broken, as well as hooves with sloughed horn. Most affected elk had severe sole ulcers with extensive laminar necrosis and pedal osteomyelitis. Histopathology of normal and abnormal hooves identified acute and chronic laminitis in all affected elk and one control elk. Hepatic copper and selenium levels in all affected and control elk were also deficient, and hoof keratin copper levels were low. No significant underlying systemic or musculoskeletal disease was detected in the affected elk, and attempts to isolate bacterial and viral pathogens were unsuccessful. A primary cause of hoof deformity was not definitively identified in this chronically affected group. Studies to identify infectious hoof disease and to characterize acute and subacute lesions are underway.

Interdigital dermatitis, heel horn erosion, and digital dermatitis in 14 Norwegian dairy herds

The aim of this study was to assess infectious foot diseases, including identification and characterization of Dichelobacter nodosus and Treponema spp., in herds having problems with interdigital dermatitis (ID) and heel horn erosion (E) and in control herds expected to have few problems. We also wanted to compare diseased and healthy cows in all herds. The study included 14 dairy herds with a total of 633 cows. Eight herds had a history of ID and E, and 6 were control herds. All cows were scored for lameness, and infectious foot diseases on the hind feet were recorded after trimming. Swabs and biopsies were taken from the skin of 10 cows in each herd for bacterial analyses. In total, samples were taken from 34 cows with ID, 11 with E, 40 with both ID and E, and 8 with digital dermatitis (DD), and from 47 cows with healthy feet. Swabs were analyzed for identification and characterization of D. nodosus by PCR, culture, virulence testing, and serotyping. Biopsies were analyzed by fluorescent in situ hybridization regarding histopathology, identification, and characterization of Treponema spp., and identification of D. nodosus. Interdigital dermatitis was the most frequent foot disease, with a prevalence of 50.4% in problem herds compared with 26.8% in control herds. Heel horn erosion was recorded in 34.8% of the cows in problem herds compared with 22.1% in control herds. Dichelobacter nodosus was detected in 97.1% of the cows with ID, in 36.4% with E, in all cows with both ID and E, in all cows with DD, and in 66.0% of cows with healthy feet. All serogroups of D. nodosus except F and M were detected, and all isolates were defined as benign by the gelatin gel test. Treponema spp. were detected in 50.0% of the cows with ID, in 9.1% with E, in 67.5% with ID and E, in all cows with DD, and in 6.4% of those with healthy feet. In total, 6 previously described phylotypes (PT) of Treponema were detected: PT1, PT3, PT6, PT13, and PT15 in cows with ID, PT1 in a cow with E, and PT1, PT2, PT3, PT6, and PT13 in cows with both ID and E. One new phylotype (PT19) was identified. The epidermal damage score was higher but the difference in inflammatory response of the dermis was minor in cows with ID versus those with healthy feet. Fisher's exact test revealed an association between ID and D. nodosus, and between ID and Treponema spp. Logistic regression revealed an association between both ID and E and dirty claws (odds ratios=1.9 and 2.0, respectively). Our study indicates that D. nodosus, Treponema spp., and hygiene are involved in the pathogenesis of ID.

The effect of slurry on skin permeability to methylene blue dye in dairy cows with and without a history of digital dermatitis

This study aimed to determine whether there was a difference in skin permeability to methylene blue dye or skin morphology between dairy cows that differed in their susceptibility to digital dermatitis (DD) and to assess the effect of contact with slurry on skin permeability. Twenty nine dairy cows were monitored for DD during the winter housing period and classed as DD+ (previous DD infection, n = 17), or DD- (no recorded infection, n = 12). The animals were culled and a skin sample was taken from above the heel of each hind foot and frozen. Samples were later defrosted and one sample from each cow was tested for permeability, whereas the other was treated with slurry for 24 h before permeability testing. To test permeability, methylene blue dye was applied to the skin surface in a Franz diffusion cell. After 48 h, the amount of dye that had passed through the skin was estimated. The stratum corneum thickness and the density of hair follicles were determined from additional heel skin samples. Skin permeability to methylene blue dye was significantly greater for samples that had been treated with slurry but did not differ between DD+ and DD- animals. No difference was found in the stratum corneum thickness or density of hair follicles between DD+ and DD- animals. These findings imply that individual differences in general skin permeability are not a major factor in determining DD susceptibility and suggest that contact with slurry could contribute to DD infection by increasing the permeability of the skin, which may facilitate pathogen entry. Further work is required to clarify the role played by slurry in the pathogenesis of DD.

Targeting the treponemal microbiome of digital dermatitis infections by high-resolution phylogenetic analyses and comparison with fluorescent in situ hybridization

Modern pyrosequencing technology allows for a more comprehensive approach than traditional Sanger sequencing for elucidating the etiology of bovine digital dermatitis. We sought to describe the composition and diversity of treponemes in digital dermatitis lesions by using deep sequencing of the V3 and V4 hypervariable regions of the 16S rRNA gene coupled with species-level taxonomic identification. Treponema-specific 16S rRNA gene PCRs and pyrosequencing were performed on biopsy specimens originating from 10 different Catalan dairy herds (n = 36) with digital dermatitis, and this analysis yielded 75,297 sequences. We identified 20 different taxa, including a potentially novel phylotype that displayed 95% sequence identity to members of the Treponema denticola/Treponema pedis-like cluster. Species frequencies and abundances that were determined by pyrosequencing analysis were highly correlated with the results of fluorescent in situ hybridization using phylotype-specific oligonucleotide probes. In a limited number of animals from a single geographic region, we detected most of the Treponema phylotypes that were described in previous investigations of digital dermatitis. Additionally, we identified a number of phylotypes that mapped to oral treponemes of humans and dogs that had not been reported for digital dermatitis lesions. The results presented here support previous observations of a polytreponemal etiology of infections, with Treponema phagedenis-like, Treponema medium/Treponema vincentii-like, and T. denticola/T. pedis-like phylotypes being highly associated with disease. Using this new approach, it has become feasible to study large herds and their surrounding environments, which might provide a basis for a better understanding of the pathogenesis of this disease.

Identifying host pathogenic pathways in bovine digital dermatitis by RNA-Seq analysis

Digital dermatitis is a painful foot disease compromising welfare in dairy cattle. The disease has a complex multibacterial aetiology, but little is known about its pathogenesis. In this study, gene expression in skin biopsies from five bovine digital dermatitis lesions and five healthy bovine feet was compared using RNA-Seq technology. Differential gene expression was determined after mapping transcripts to the Btau 4.0 genome. Pathway analysis identified gene networks involving differentially expressed transcripts. Bovine digital dermatitis lesions had increased expression of mRNA for α2-macroglobulin-like 1, a protein potentially involved in bacterial immune evasion and bacterial survival. There was increased expression of keratin 6A and interleukin 1β mRNA in bovine digital dermatitis lesions, but reduced expression of most other keratin and keratin-associated genes. There was little evidence of local immune reactions to the bacterial infection present in lesions.