Sites of persistence of Fusobacterium necrophorum and Dichelobacter nodosus: a paradigm shift in understanding the epidemiology of footrot in sheep

Footbathing and Foot Trimming, and No Quarantine: Risks for High Prevalence of Lameness in a Random Sample of 269 Sheep Flocks in England, 2022

Since 2004, the prevalence of lameness in sheep flocks in England has reduced as farmers have adopted evidence-based management practices to control lameness. In 2011, the Farm Animal Welfare Council proposed a target prevalence of <2% lameness in sheep by 2021. This study investigated whether that target had been achieved and determined which practices were associated with prevalence of lameness. A postal questionnaire was sent to 1000 randomly selected farmers to investigate the prevalence of lameness and management practices in 2022. The geometric mean prevalence of lameness was <2% in ewes and lambs, but the median was 3%; approximately 26% flocks had <2% lameness. Data were analysed using robust variable selection with multivariable linear models. Farmers that quarantined ewes for ≥3 weeks and did not use foot bathing or foot trimming to prevent lameness had 40-50% lower prevalence of lameness than those not using these practices. Fewer farmers (19.0%) were always using parenteral antimicrobials to treat footrot, an effective practice, than in previous research (49.7%). We conclude that the target of <2% lameness in England has been achieved by 26% of farmers, and further work is required for more farmers to follow the evidence-based management practices to minimise lameness.

Quantifying and mapping digital dermatitis-associated bacteria in lesion and nonlesion body sites and dairy farm environment

The source of infection of digital dermatitis (DD), an infectious lameness condition, is still uncertain. In this cross-sectional study, we aimed to identify potential reservoirs of DD bacteria in dairy cattle body sites with different stages of the disease and farm environments. We collected skin swabs from 85 dairy cows from 5 herds, 3 with and 2 without DD, from foot, hock, and udder cleft skin (with lesions or not), saliva, urine, and feces. We also obtained environmental samples. Real-time quantitative PCR targeted Treponema phagedenis, Treponema medium, Treponema pedis, Porphyromonas levii, Bacteroides pyogenes, Fusobacterium necrophorum, and Fusobacterium mortiferum. Digital dermatitis-associated Treponema spp. were exclusively detected in DD-affected herds in DD-foot and other skin lesions, healthy skin, saliva, and environmental samples. In contrast, the non-Treponema spp. were found in samples from both DD-negative and affected herds. As expected, DD lesions had higher bacterial loads than healthy skin. Interestingly, similar counts were observed in udder cleft lesions, indicating a potential opportunistic behavior on compromised skin. None of the targeted species were detected in fecal samples, but P. levii, B. pyogenes, and F. necrophorum were detected in urine. All 7 species were detected in saliva, although in low quantities. No associations were observed between the presence of each bacterial species in DD lesions and urine; however, there was an association between the presence of DD-Treponema spp. in lesions and saliva, hock, and udder skin. Feces and urine do not seem to be a DD bacteria primary source, but saliva and other skin lesions may play a role. Longitudinal studies would improve our understanding of DD-associated bacteria's transient or persistent presence in these sites. Investigating the sources of DD-associated bacteria will guide future interventions to minimize bacterial shedding and transmission, ultimately more effectively reducing bacterial load, transmission, and sources of infection in dairy herds.

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.

Genome-wide association with footrot in hair and wool sheep

Ovine footrot is an infectious disease with important contributions from Dichelobacter nodosus and Fusobacterium necrophorum. Footrot is characterized by separation of the hoof from underlying tissue, and this causes severe lameness that negatively impacts animal wellbeing, growth, and profitability. Large economic losses result from lost production as well as treatment costs, and improved genetic tools to address footrot are a valuable long-term goal. Prior genetic studies had examined European wool sheep, but hair sheep breeds such as Katahdin and Blackbelly have been reported to have increased resistance to footrot, as well as to intestinal parasites. Thus, footrot condition scores were collected from 251 U.S. sheep including Katahdin, Blackbelly, and European-influenced crossbred sheep with direct and imputed genotypes at OvineHD array (>500,000 single nucleotide polymorphism) density. Genome-wide association was performed with a mixed model accounting for farm and principal components derived from animal genotypes, as well as a random term for the genomic relationship matrix. We identified three genome-wide significant associations, including SNPs in or near GBP6 and TCHH. We also identified 33 additional associated SNPs with genome-wide suggestive evidence, including a cluster of 6 SNPs in a peak near the genome-wide significance threshold located near the glutamine transporter gene SLC38A1. These findings suggest genetic susceptibility to footrot may be influenced by genes involved in divergent biological processes such as immune responses, nutrient availability, and hoof growth and integrity. This is the first genome-wide study to investigate susceptibility to footrot by including hair sheep and also the first study of any kind to identify multiple genome-wide significant associations with ovine footrot. These results provide a foundation for developing genetic tests for marker-assisted selection to improve resistance to ovine footrot once additional steps like fine mapping and validation are complete.

Characterization of Three New Outer Membrane Adhesion Proteins in Fusobacterium necrophorum

Fusobacterium necrophorum, an anaerobic Gram-negative pathogen, causes necrotic cattle infections, impacting livestock health and the US feedlot industry. Antibiotic administration is the mainstay for treating F. necrophorum infections, although resistance hampers their effectiveness. Vaccination, especially targeting outer membrane proteins (OMPs) due to their antigenic properties and host specificity, offers an alternative to antibiotics. This study identified high-binding-affinity adhesion proteins from F. necrophorum using binding and pull-down assays with bovine adrenal gland endothelial cells (EJG). Four OMP candidates (17.5 kDa/OmpH, 22.7 kDa/OmpA, 66.3 kDa/cell surface protein (CSP), and a previously characterized 43 kDa OMP) were expressed as recombinant proteins and purified. Rabbit polyclonal antibodies to recombinant OMPs were generated, and their ability to inhibit bacterial binding in vitro was assessed. The results show that treatment with individual polyclonal antibodies against 43 kDa significantly inhibited bacterial adhesion, while other antibodies were less potent. However, combinations of two or more antibodies showed a more prominent inhibitory effect on host-cell adhesion. Thus, our findings suggest that the identified OMPs are involved in fusobacterial attachment to host cells and may have the potential to be leveraged in combination for vaccine development. Future in vivo studies are needed to validate their roles and test the feasibility of an OMP-based subunit vaccine against fusobacterial infections.

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.

Outer-Membrane Vesicles of Fusobacterium necrophorum: A Proteomic, Lipidomic, and Functional Characterization

Outer-membrane vesicles (OMVs) are extruded nanostructures shed by Gram-negative bacteria, containing periplasmic contents, and often including virulence factors with immunogenic properties. To assess their potential for use in vaccine development, we purified OMVs from the Fusobacterium necrophorum subspecies necrophorum, an opportunistic necrotic infection-causing pathogen, and characterized these structures using proteomics, lipid-profiling analyses, and cytotoxicity assays. A proteomic analysis of density-gradient-purified F. necrophorum OMVs identified 342 proteins, a large proportion of which were outer-membrane proteins (OMPs), followed by cytoplasmic proteins, based on a subcellular-localization-prediction analysis. The OMPs and toxins were among the proteins with the highest intensity identified, including the 43-kDa-OMP-, OmpA-, and OmpH-family proteins, the cell-surface protein, the FadA adhesin protein, the leukotoxin-LktA-family filamentous adhesin, the N-terminal domain of hemagglutinin, and the OMP transport protein and assembly factor. A Western blot analysis confirmed the presence of several OMPs and toxins in the F. necrophorum OMVs. The lipid-profiling analysis revealed phospholipids, sphingolipids, and acetylcarnitine as the main lipid contents of OMVs. The lactate-dehydrogenase-cytotoxicity assays showed that the OMVs had a high degree of cytotoxicity against a bovine B-lymphocyte cell line (BL-3 cells). Thus, our data suggest the need for further studies to evaluate the ability of OMVs to induce immune responses and assess their vaccine potential in vivo.

The prevalence, virulence, and serogroups of Dichelobacter nodosus and prevalence of Fusobacterium necrophorum in footrot lesions of sheep and cattle in Morocco

Background and Aim: Footrot is a contagious disease of ruminants leading to severe economic losses. This study aimed to estimate the prevalence, virulence, and serogroups of Dichelobacter nodosus and the prevalence of Fusobacterium necrophorum in footrot lesions of sheep and cattle. Materials and Methods: A total of 106 pathogenic lesion samples were taken from 74 sheep and 32 cattle exhibiting typical footrot lesions and were analyzed for the presence of D. nodosus and F. necrophorum by real-time polymerase chain reaction (PCR). Both virulence and serogroup were estimated for D. nodosus positive samples. Results: Among the 106 samples, 89 were positive by PCR for F. necrophorum, D. nodosus, or both. Dichelobacter nodosus was detected at a rate of 78.3% versus 28.3% for F. necrophorum. Virulent D. nodosus strains were detected in 67.5% of positive samples, with a higher rate in sheep (73.4%) than in cattle (47.4%). Benign D. nodosus strains were detected in 57.8% of samples, with a lower prevalence rate in sheep (50%) than in cattle (84.2%). The positive samples of D. nodosus revealed the presence of three dominant serogroups (D, H, I) and three minor serogroups (G, C, A) by serogroup-specific multiplex PCR. Conclusion: The findings provided information on the prevalence of D. nodosus and F. necrophorum strains in footrot lesions of sheep and cattle in some regions of Morocco, which will be useful for developing an effective autovaccine for the prevention of this disease in cattle and sheep in these regions. Keywords: cattle, Dichelobacter nodosus, footrot, Fusobacterium necrophorum, polymerase chain reaction, sheep.

NF-κB signaling pathway mechanism in cow intertoe skin inflammation caused by Fusobacterium necrophorum

Background

Fusobacterium necrophorum is the main pathogen inducing bovine foot rot. The infected site is often accompanied by a strong inflammatory response, but the specific inflammatory regulatory mechanism remains unclear.

Aim

A cow skin explants model was established to elucidate the mechanism of F. necrophorum bacillus causing foot rot in cows, and to provide reference for future clinical practice.

Methods

Cow intertoe skin explants were cultured in vitro, and F. necrophorum bacteria solution and nuclear factor-κB (NF-κB) inhibitor BAY 1-7082 were added to establish an in vitro infection model. Hematoxylin and eosin staining, terminal - deoxynucleotidyl transferase mediated nick end labeling, and immunohistochemistry were used to detect the pathological changes of the skin explants infected with F. necrophorum, the degree of tissue cell apoptosis, and the expression of the apoptosis-related protein Caspase-3, respectively. RT-qPCR, Western blot, and ELISA were used to detect the activation of the NF-κB pathway and inflammatory cytokines by F. necrophorum.

Results

The intertoe skin structure of cows infected with F. necrophorum changed with different degrees of inflammation, and the degree of tissue cell apoptosis was significantly increased (P < 0.01). In addition, infection with F. necrophorum significantly increased the phosphorylation level of IκBα protein and up-regulated the expression level of NF-κB p65. The high expression and transcriptional activity of NF-κB p65 significantly increased the expression and concentration of the inflammatory cytokines TNF-α, IL-1β, and IL-8, thus inducing the occurrence of an inflammatory response. However, inhibition of NF-κB p65 activity significantly decreased the expression of inflammatory factors in the intertoe skin of cows infected with F. necrophorum.

Conclusion

F. necrophorum activates NF-κB signaling pathway by increasing the expression of TNF-α, IL-1β, IL-8 and other inflammatory factors, leading to foot rot in dairy cows.

Social behaviour and transmission of lameness in a flock of ewes and lambs

INTRODUCTION

Sheep have heterogenous social connections that influence transmission of some infectious diseases. Footrot is one of the top five globally important diseases of sheep, it is caused by Dichelobacter nodosus and transmits between sheep when infectious feet contaminate surfaces, e.g., pasture. Surfaces remain infectious for a few minutes to a few days, depending on surface moisture levels. Susceptible sheep in close social contact with infectious sheep might be at risk of becoming infected because they are likely to step onto infectious footprints, particularly dams and lambs, as they cluster together.

METHODS

High resolution proximity sensors were deployed on 40 ewes and their 54 lambs aged 5-27 days, in a flock with endemic footrot in Devon, UK for 13 days. Sheep locomotion was scored daily by using a 0-6 integer scale. Sheep were defined lame when their locomotion score (LS) was ≥2, and a case of lameness was defined as LS ≥2 for ≥2 days.

RESULTS

Thirty-two sheep (19 ewes, 9 single, and 4 twin lambs) became lame during the study, while 14 (5 ewes, 5 single, and 4 twin lambs) were lame initially. These 46 sheep were from 29 family groups, 14 families had >1 lame sheep, and transmission from ewes to lambs was bidirectional. At least 15% of new cases of footrot were from within family transmission; the occurrence of lameness was higher in single than twin lambs. At least 4% of transmission was due to close contact across the flock. Most close contact occurred within families. Single and twin lambs spent 1.5 and 0.9 hours/day with their dams, respectively, and twin lambs spent 3.7 hours/day together. Non-family sheep spent only 0.03 hours/day in contact. Lame single lambs and ewes spent less time with non-family sheep, and lame twin lambs spent less time with family sheep.

DISCUSSION

We conclude that most transmission of lameness is not attributable to close contact. However, in ewes with young lambs, some transmission occurs within families and is likely due to time spent in close contact, since single lambs spent more time with their dam than twin lambs and were more likely to become lame.

Natural Mycoplasma Infection Reduces Expression of Pro-Inflammatory Cytokines in Response to Ovine Footrot Pathogens

Ovine footrot is a complex multifactorial infectious disease, causing lameness in sheep with major welfare and economic consequences. Dichelobacter nodosus is the main causative bacterium; however, footrot is a polymicrobial disease with Fusobacterium necrophorum, Mycoplasma fermentans and Porphyromonas asaccharolytica also associated. There is limited understanding of the host response involved. The proinflammatory mediators, interleukin (IL)-1β and C-X-C Motif Chemokine Ligand 8 (CXCL8), have been shown to play a role in the early response to D. nodosus in dermal fibroblasts and interdigital skin explant models. To further understand the response of ovine skin to bacterial stimulation, and to build an understanding of the role of the cytokines and chemokines identified, primary ovine interdigital fibroblasts and keratinocytes were isolated, cultured and stimulated. The expression of mRNA and protein release of CXCL8 and IL-1β were measured after stimulation with LPS, D. nodosus or F. necrophorum, which resulted in increased transcript levels of IL-1β and CXCL8 in the M. fermentans-free cells. However, only an increase in the CXCL8 protein release was observed. No IL-1β protein release was detected, despite increases in IL-1β mRNA, suggesting the signal for intracellular pre-IL-1β processing may be lacking when culturing primary cells in isolation. The keratinocytes and fibroblasts naturally infected with M. fermentans showed little response to the LPS, a range of D. nodosus preparations or heat-inactivated F. necrophorum. Primary single cell culture models complement ex vivo organ culture models to study different aspects of the host response to D. nodosus. The ovine keratinocytes and fibroblasts infected with M. fermentans had a reduced response to the experimental bacterial stimulation. However, in the case of footrot where Mycoplasma spp. are associated with diseased feet, this natural infection gives important insights into the impact of multiple pathogens on the host response.

Nasopulmonary mites (Acari: Halarachnidae) as potential vectors of bacterial pathogens, including Streptococcus phocae, in marine mammals

Nasopulmonary mites (NPMs) of the family Halarachnidae are obligate endoparasites that colonize the respiratory tracts of mammals. NPMs damage surface epithelium resulting in mucosal irritation, respiratory illness, and secondary infection, yet the role of NPMs in facilitating pathogen invasion or dissemination between hosts remains unclear. Using 16S rRNA massively parallel amplicon sequencing of six hypervariable regions (or “16S profiling”), we characterized the bacterial community of NPMs from 4 southern sea otters (Enhydra lutris nereis). This data was paired with detection of a priority pathogen, Streptococcus phocae, from NPMs infesting 16 southern sea otters and 9 California sea lions (Zalophus californianus) using nested conventional polymerase chain reaction (nPCR). The bacteriome of assessed NPMs was dominated by Mycoplasmataceae and Vibrionaceae, but at least 16 organisms with pathogenic potential were detected as well. Importantly, S. phocae was detected in 37% of NPM by nPCR and was also detected by 16S profiling. Detection of multiple organisms with pathogenic potential in or on NPMs suggests they may act as mechanical vectors of bacterial infection for marine mammals.

Risk factors associated with the infection of sheep with Dichelobacter nodosus

Ovine footrot is a highly contagious foot disease caused by the gram-negative bacterium Dichelobacter nodosus (D. nodosus). In a recent report, we showed a prevalence of 42.9% D. nodosus positive swabs across Germany. In this follow-up study, we used real-time PCR results for D. nodosus and footrot scores of 9297 sheep from 208 flocks and collated these data with survey data on herd and animal characteristics and herd management. The aims of the present study were to investigate herd and animal factors associated with D. nodosus infection and footrot scores in individual sheep. Multivariable analyses with generalized mixed models showed that month of recording, breed, herdbook membership, use of antibiotics, and footbaths in the past 3–10 years, signs of footrot in the past 12 months and flock environment of the sheep, modelled as a random farm effect within region, were significant risk factors. Among the 21 different breeds, Romney had the lowest risk of D. nodosus infection, while Swifter had the highest risk and German Merino and German White Heath were the next breeds at highest risk of D. nodosus infection. The variance between farms in the prevalence of D. nodosus was large and accounted for 84% of the total variance in the mixed model analysis. We conclude that specific and as yet unknown effects influencing D. nodosus infections in flocks, as well as breed and weather, are the most important effects on D. nodosus infection in sheep, pointing towards the need to establish adequate infection control at farm level.

Differences in composition of interdigital skin microbiota predict sheep and feet that develop footrot

Footrot has a major impact on health and productivity of sheep worldwide. The current paradigm for footrot pathogenesis is that physical damage to the interdigital skin (IDS) facilitates invasion of the essential pathogen Dichelobacter nodosus. The composition of the IDS microbiota is different in healthy and diseased feet, so an alternative hypothesis is that changes in the IDS microbiota facilitate footrot. We investigated the composition and diversity of the IDS microbiota of ten sheep, five that did develop footrot and five that did not (healthy) at weekly intervals for 20 weeks. The IDS microbiota was less diverse on sheep 2 + weeks before they developed footrot than on healthy sheep. This change could be explained by only seven of > 2000 bacterial taxa detected. The incubation period of footrot is 8–10 days, and there was a further reduction in microbial diversity on feet that developed footrot in that incubation period. We conclude that there are two stages of dysbiosis in footrot: the first predisposes sheep to footrot and the second occurs in feet during the incubation of footrot. These findings represent a step change in our understanding of the role of the IDS microbiota in footrot pathogenesis.

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.

Impact of Strain Variation of Dichelobacter nodosus on Disease Severity and Presence in Sheep Flocks in England

AprV2 and aprB2 are variants of the apr gene of Dichelobacter nodosus, the cause of footrot in sheep. They are putative markers for severe and mild disease expression. The aim of our study was to investigate the distribution of aprV2 and aprB2 in flocks with and without footrot. Our hypotheses were that both strains are present in endemically affected flocks, with aprB2 and aprV2 associated with mild and virulent phenotypes respectively but that D. nodosus is not present in flocks without footrot. Alternatively, aprB2 persists in flocks without footrot. Despite extensive searching over 3 years only three flocks of sheep without footrot were identified. D. nodosus was not detected in these three flocks. In one further flock, only mild interdigital dermatitis was observed, and only aprB2 was detected. Twenty-four flocks with endemic footrot of all severities were sampled on three occasions and all were positive for D. nodosus and the aprV2 variant; aprB2 was detected in only 11 of these flocks. AprB2 was detected as a co-infection with aprV2 in the 22% of samples positive for aprB2 and was more likely in mild footrot phenotypes than severe. Dichelobacter nodosus serogroups were not associated with footrot phenotype. We conclude that D. nodosus, even aprB2 strains, do not persist in flocks in the absence of footrot. Our results support the hypothesis that aprB2 is associated with mild footrot phenotypes. Finally, we conclude that given the small number of flocks without footrot that were identified, footrot is highly endemic in English sheep flocks.

OCCURRENCE OF FOOTROT IN FREE-RANGING ALPINE IBEX (CAPRA IBEX) COLONIES IN SWITZERLAND

Footrot is a worldwide economically important, debilitating disease caused by Dichelobacter nodosus. In sheep (Ovis aries), it is characterized by lesions of varying severity, depending on the strain, whereas Alpine ibex (Capra ibex) seem to develop severe lesions, whatever the strain. Healthy carriers occur in livestock but are rare in wild ruminants. Using a triangulation approach (retrospective questionnaire survey, necropsy database screening, and pathogen prevalence estimation in selected ibex colonies with and without footrot), we aimed at evaluating the importance of footrot in the ibex population, identifying potential risk factors for disease occurrence in this species, and defining the epidemiological role of ibex. Our study revealed that footrot occurs throughout the entire ibex territory (34% of the Swiss ibex colonies affected) but only as a sporadic disease (mostly one case per disease event), although the situation differed among footrot-positive colonies because half of them had experienced outbreak recurrences. Risk factor analysis for the occurrence of footrot in ibex colonies suggested an absence of an effect of meteorologic conditions, region, contacts with sheep or cattle (known to be very common healthy carriers of D. nodosus) and existing local disease control program. We found a significant effect only of contacts with sheep having footrot. Pathogen prevalence was very low in all investigated colonies. In conclusion, our results support previous data suggesting that ibex are susceptible spillover hosts, likely infected mainly by sympatric sheep displaying clinical signs.

Multiple model triangulation to identify factors associated with lameness in British sheep flocks

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Multiple model triangulation identifies variables that are likely true positives.

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Triangulation increases confidence in which managements to recommend in practice.

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Effective management of ewes can lower prevalence of lameness in ewes and lambs.

Identification of factors associated with an outcome can be challenging when the number of explanatory variables is large in relation to the number of observations. Multiple model triangulation, where results from several model types are combined, improves the likelihood of identifying true predictor variables. The aim of this study was to use triangulation to identify covariates likely to be truly associated with the prevalence of lameness in sheep flocks in Great Britain.

Data were collected using a questionnaire sent to 3200 sheep farmers in Great Britain in 2018. The useable response rate was 14.1 %. The geometric mean prevalence of lameness was 1.4 % (95 % CI 1.2−1.7) for ewes, and 0.6 % (95 % CI 0.5−0.9) for lambs, however, approximately 60 % flocks had >2% prevalence of lameness in ewes.

Four model types were investigated, two generalised linear models (negative binomial and quasi-Poisson) built using stepwise selection, and two elastic net models (Poisson and Gaussian distributions) refined with selection stability estimation.

Triangulated covariates were those selected in three or all four models – 10 for ewes and 12 for lambs. Higher prevalence of lameness in ewes was associated with 5−100% feet bleeding during routine foot trimming compared with not foot trimming, footbathing the flock to treat severe footrot (SFR) and always using formalin in footbaths, both compared with not footbathing, using FootVax™ for <1 year compared with not using FootVax™, and never quarantining new or returning sheep to the farm for >3 weeks compared with always. Lower prevalence of lameness in ewes was associated with vaccinating with FootVax™ for >5 years compared with not vaccinating, peat soil compared with no peat soil, and having no lame ewes to treat.

Higher prevalence of lameness in lambs was associated with 5−100% feet bleeding during routine foot trimming, always foot trimming ewes with SFR, not knowingly selecting replacement ewes from ewes that were never lame compared with always, replacement sheep purchased and homebred compared with only homebred, treating lambs >3 days after recognition of lameness compared with 0-3 days and footbathing the flock to treat interdigital dermatitis compared with not footbathing at all. Lower prevalence of lameness in lambs was associated with peat soil, flocks in Scotland versus England, an altitude of >230−500 m compared with ≤230 m, never using antibiotic injection to treat lambs with SFR compared with always, and having no lame lambs to treat.

We conclude triangulation identified reliable management practices for farmers to implement to minimise lameness in sheep.

A Cross-Sectional Epizootiological Study and Risk Assessment of Foot-Related Lesions and Lameness in Intensive Dairy Sheep Farms

Simple Summary

Foot-related lameness is one of the most significant welfare issues in farm animals. Contrary to dairy cows and meat sheep breeds, epizootiological data on foot-lesions and associated lameness in dairy sheep are scarce. In this study, data were collected from 30 representative intensive dairy sheep farms. Multivariate statistical analysis was used to produce a typology of intensive farming systems which resulted in the assignment of farms in two distinct clusters. Six hundred adult ewes were randomly selected from six flocks (three flocks per cluster) and a cross-sectional study was implemented to investigate the epizootiology and potential risk factors of foot-related lameness, foot-lesions and diseases. Ovine interdigital dermatitis and infectious footrot were the most common infectious foot diseases, while white line disease and hoof wall cracks were the most prevalent non-infectious lesions. Infectious footrot was the main cause of lameness and increased with age, whereas body condition score was associated with increased prevalence of ovine interdigital dermatitis. Comparisons between the clusters regarding foot-related lameness, foot-diseases and lesions at the animal, the limb, and the hoof level are presented, and relevant literature, mechanisms, hypotheses, and challenges of the field are discussed.

Abstract

Foot-related lameness, foot-diseases and lesions are emerging issues in dairy sheep; however, relevant epizootiological studies are scarce, and risk factors have not been elucidated. The objectives of this cross-sectional study were (i) to address this dearth of knowledge by investigating the epizootiology of lameness-related foot-lesions and diseases, and (ii) to assess the impact of potential risk factors on foot health, in intensive dairy sheep farms. Thirty farms were assigned in two representative clusters using a multivariate statistical analysis. Three farms per cluster and 100 multiparous milking ewes per farm (total n = 600) were selected and enrolled in the study. Foot-related lameness, ovine interdigital dermatitis (OID), infectious footrot (IFR), white line disease, hoof wall cracks, as well as health and welfare traits were recorded. Overall prevalence of foot-related lameness was 9.0% and was primarily associated with IFR; however, additional infectious and non-infectious foot diseases and lesions also contributed. Among infectious foot diseases, OID was the most prevalent (21.3%) followed by IFR (8.0%); WLD and hoof wall cracks were the most prevalent non-infectious foot-lesions (37.7% and 15.3%, respectively). IFR and OID prevalence increased with age (p < 0.05) and BCS (p < 0.01), respectively, suggesting that host-related factors and husbandry practices are important determinants of its occurrence.

Characterisation of Dichelobacter nodosus on Misshapen and Damaged Ovine Feet: A Longitudinal Study of Four UK Sheep Flocks

Simple Summary

The bacterium Dichelobacter nodosus is the cause of footrot in sheep: a painful, contagious foot disease. Some sheep may be more susceptible to carrying D. nodosus on their feet, despite showing no signs of disease, and pose a risk to flock health and welfare. This study investigated whether misshapen or damaged feet (poor hoof conformation) were more likely to have D. nodosus present and in greater quantities than feet in good condition. Eighty-five ewes from four flocks were examined three times, on average, across a 12-month period. Poor hoof conformation traits were observed in over 92% of foot observations. Feet with poor sole and heel conformation were more likely to have higher quantities of D. nodosus than those in good conformation. Furthermore, on feet positive for D. nodosus, wall overgrowth contributed towards higher D. nodosus load. We highlight feet with aspects of poor conformation traits to covertly harbour D. nodosus. These feet could transmit D. nodosus to other feet of sheep. Increasing our understanding of D. nodosus infection is crucial in helping farmers improve management practices to reduce footrot.

Abstract

Dichelobacter nodosus is the causal agent of ovine footrot, a contagious disease of welfare and economic concern worldwide. Damaged feet may be subclinical carriers of D. nodosus and covertly spread infection. Accordingly, we evaluated the risk of misshapen and damaged feet on D. nodosus presence and load in four commercial UK sheep flocks. Foot-level observations and swabs (n = 972) were collected from ewes (n = 85) over 12 months. On average, ewes were sampled three times. Feet were inspected for disease and scored (good/poor) for three hoof conformation traits (sole and heel, wall, and wall overgrowth). Swabs were analysed for presence and load of D. nodosus, and mixed models were constructed. Poor hoof conformation traits were present in 92.5% of foot-level observations. Feet with poor sole and heel conformation were more likely to have higher D. nodosus loads (β = 0.19, 95% CI: 0.04–0.35) than those with good conformation. Furthermore, on feet positive for D. nodosus, wall overgrowth was associated with higher D. nodosus loads (β = 0.27, 95% CI: 0.01–0.52). Feet with aspects of poor conformation covertly harbour D. nodosus and are a source of infection. Flock management should be guided by hoof conformation to reduce disease challenge.

Effects of supplemental feeding on the fecal bacterial communities of Rocky Mountain elk in the Greater Yellowstone Ecosystem

Supplemental feeding of wildlife is a common practice often undertaken for recreational or management purposes, but it may have unintended consequences for animal health. Understanding cryptic effects of diet supplementation on the gut microbiomes of wild mammals is important to inform conservation and management strategies. Multiple laboratory studies have demonstrated the importance of the gut microbiome for extracting and synthesizing nutrients, modulating host immunity, and many other vital host functions, but these relationships can be disrupted by dietary perturbation. The well-described interplay between diet, the microbiome, and host health in laboratory and human systems highlights the need to understand the consequences of supplemental feeding on the microbiomes of free-ranging animal populations. This study describes changes to the gut microbiomes of wild elk under different supplemental feeding regimes. We demonstrated significant cross-sectional variation between elk at different feeding locations and identified several relatively low-abundance bacterial genera that differed between fed versus unfed groups. In addition, we followed four of these populations through mid-season changes in supplemental feeding regimes and demonstrated a significant shift in microbiome composition in a single population that changed from natural forage to supplementation with alfalfa pellets. Some of the taxonomic shifts in this population mirrored changes associated with ruminal acidosis in domestic livestock. We discerned no significant changes in the population that shifted from natural forage to hay supplementation, or in the populations that changed from one type of hay to another. Our results suggest that supplementation with alfalfa pellets alters the native gut microbiome of elk, with potential implications for population health.

Ovine footrot: A review of current knowledge

Footrot is a contagious foot disease mainly affecting sheep. It is caused by the Gram-negative anaerobic bacterium Dichelobacter nodosus. Warm, wet environmental conditions favour development of footrot, and under perfect conditions, it takes just 2-3 weeks from infection to manifestation of clinical signs. Affected sheep show lameness of various degrees and often graze while resting on their carpi. Local clinical signs vary in severity and extent from interdigital inflammation (benign footrot) to underrunning of the complete horn shoe in advanced stages of virulent footrot. Laboratory diagnosis ideally involves collection of four-foot interdigital swab samples followed by competitive real time PCR, allowing for detection of the presence of D. nodosus and differentiation between benign and virulent strains. Laboratory-based diagnostics at the flock level based on risk-based sampling and pooling of interdigital swab samples are recommended. The list of treatment options of individual sheep includes careful removal of the loose undermined horn, local or systemic administration of antimicrobials, systemic administration of non-steroidal anti-inflammatories (NSAIDs) and disinfectant footbathing. Strategies for control at the flock level are manifold and depend on the environmental conditions and the procedures traditionally implemented by the respective country. Generally, measures consist of treatment/culling of infected sheep, vaccination and prevention of reinfection of disease-free flocks. Gaining deeper insight into the beneficial effects of NSAIDs, screening for eco-friendly footbath solutions, developing better vaccines, including the development of a robust, reproducible infection model and elucidation of protective immune responses, as well as the elaboration of effective awareness training programs for sheep farmers, are relevant research gaps.

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

BACKGROUND

Contagious Ovine Digital Dermatitis (CODD) is an emerging and common infectious foot disease of sheep which causes severe welfare and economic problems for the sheep industry. The aetiology of the disease is not fully understood and control of the disease is problematic. The aim of this study was to investigate the polybacterial aetiopathogenesis of CODD and the effects of antibiotic treatment, in a longitudinal study of an experimentally induced disease outbreak using a 16S rRNA gene amplicon sequencing approach.

RESULTS

CODD was induced in 15/30 experimental sheep. During the development of CODD three distinct phenotypic lesion stages were observed. These were an initial interdigital dermatitis (ID) lesion, followed by a footrot (FR) lesion, then finally a CODD lesion. Distinct microbiota were observed for each lesion in terms of microbial diversity, clustering and composition. Porphyromonadaceae, Family XI, Veillonellaceae and Fusobacteriaceae were significantly associated with the diseased feet. Veillonellaceae and Fusobacteriaceae were most associated with the earlier stages of ID and footrot rather than CODD. Following antibiotic treatment of the sheep, the foot microbiota showed a strong tendency to return to the composition of the healthy state. The microbiota composition of CODD lesions collected by swab and biopsy methods were different. In particular, the Spirochaetaceae family were more abundant in samples collected by the biopsy method, suggesting that these bacteria are present in deeper tissues of the diseased foot.

CONCLUSION

In this study, CODD presented as part of a spectrum of poly-bacterial foot disease strongly associated with bacterial families Porphyromonadaceae, Family XI (a family in Clostridiales also known as Clostridium cluster XI), Veillonellaceae and Fusobacteriaceae which are predominately Gram-negative anaerobes. Following antibiotic treatment, the microbiome showed a strong tendency to return to the composition of the healthy state. The composition of the healthy foot microbiome does not influence susceptibility to CODD. Based on the data presented here and that CODD appears to be the severest end stage of sheep infectious foot disease lesions, better control of the initial ID and FR lesions would enable better control of CODD and enable better animal welfare.

A Pilot Study to Investigate the Feasibility of a Multiple Locus Variable Number Tandem Repeat Analysis to Understand the Epidemiology of Dichelobacter nodosus in Ovine Footrot

Dichelobacter nodosus is the essential pathogen in ovine footrot, an important cause of lameness in sheep that reduces productivity and welfare. The aim of this study was to investigate the feasibility of using multiple locus variable number tandem repeat analysis (MLVA) developed to investigate isolates to understand the molecular epidemiology of Dichelobacter nodosus in ovine footrot by investigation of communities of strains. MLVA sensitivity was improved by optimizing PCR conditions to 100% specificity for D. nodosus. The improved MLVA scheme was used to investigate non-cultured DNA purified from swabs (swab DNA) and cultured DNA from isolates (isolate DNA) from 152 foot and 38 gingival swab samples from 10 sheep sampled on four occasions in a longitudinal study. Isolate DNA was obtained from 6/152 (3.9%) feet and 5/6 yielded complete MLVA profiles, three strains were detected. Two of the three isolate strains were also detected in isolate DNA from 2 gingival crevice cultures. Complete MLVA profiles were obtained from swab DNA from 39 (25.7%) feet. There were 22 D. nodosus community types that were comprised of 7 single strain and 15 multi-strain communities. Six community types were detected more than once and three of these were detected on the same four sheep and the same two feet over time. There were a minimum of 17 and a maximum of 25 strain types of D. nodosus in the study. The three isolate strain types were also the most frequently detected strain types in swab DNA. We conclude that the MLVA from swab DNA detects the same strains as culture, is much more sensitive and can be used to describe and differentiate communities and strains on sheep, feet and over time. It is therefore a sensitive molecular tool to study D. nodosus strains directly from DNA without culture.

Management Practices Associated With Prevalence of Lameness in Lambs in 2012-2013 in 1,271 English Sheep Flocks

The evidence base for management practices associated with low prevalence of lameness in ewes is robust. Current best practice is prompt treatment of even mildly lame sheep with parenteral and topical antibiotics with no routine or therapeutic foot trimming and avoiding routine footbathing. To date, comparatively little is known about management of lameness in lambs. Data came from a questionnaire completed by 1,271 English sheep farmers in 2013. Latent class (LC) analyses were used to investigate associations between treatment of footrot and geometric mean flock prevalence of lameness (GMPL) in lambs and ewes, with multinomial models used to investigate effects of flock management with treatment. Different flock typologies were identified for ewes and lambs. In both ewe and lamb models, there was an LC (1) with GMPL <2%, where infectious causes of lameness were rare, and farmers rarely treated lame animals. There was a second LC in ewes only (GMPL 3.2%) where infectious causes of lameness were present but farmers followed "best practice" and apparently controlled lameness. In other typologies, farmers did not use best practice and had higher GMPL than LC1 (3.9-4.2% and 2.8-3.5%, respectively). In the multinomial model, farmers were more likely to use parenteral antibiotics to treat lambs when more than 2-5% of lambs were lame compared with ≤2%. Once >10% of lambs were lame, while farmers were likely to use parenteral antibiotics, only sheep with locomotion score >2 were considered lame, leaving lame sheep untreated, potentially allowing spread of footrot. These farmers also used poor practices of routine foot trimming and footbathing, delayed culling, and poor biosecurity. We conclude there are no managements beneficial to manage lameness in lambs different from those for ewes; however, currently lameness in lambs is not treated using "best practice." In flocks with <2% prevalence of all lameness, where infectious causes of lameness were rare, farmers rarely treated lame animals but also did not practice poor managements of routine foot trimming or footbathing. If more farmers adopted "best practice" in ewes and lambs, the prevalence of lameness in lambs could be reduced to <2%, antibiotic use would be reduced, and sheep welfare would be improved.

Serogroups of Dichelobacter nodosus, the cause of footrot in sheep, are randomly distributed across England

We present the largest and most representative study of the serological diversity of Dichelobacter nodosus in England. D. nodosus causes footrot and is one of the top five globally important diseases of sheep. The commercial vaccine, containing nine serogroups, has low efficacy compared with bivalent vaccines. Our aim was to investigate the prevalence and distribution of serogroups of D. nodosus in England to elucidate whether a bivalent vaccine could protect the national flock. Farmers from 164 flocks submitted eight interdigital swabs from eight, preferably diseased, sheep. All serogroups, A-I, were detected by PCR in 687/1150 D. nodosus positive swabs, with a prevalence of 2.6-69.3% of positive swabs per serogroup. There was a median of two serogroups per flock (range 0-6). Serogroups were randomly distributed between, but clustered within, flocks, with 50 combinations of serogroups across flocks. H and B were the most prevalent serogroups, present in > 60% of flocks separately but in only 27% flocks together. Consequently, a bivalent vaccine targeting these two serogroups would protect 27% of flocks fully (if only H and B present) and partially, if more serogroups were present in the flock. We conclude that one bivalent vaccine would not protect the national flock against footrot and, with 50 combinations of serogroups in flocks, flock-specific vaccines are necessary.