Ovine footrot: new approaches to an old disease

Genome-wide association study identifies genetic variants underlying footrot in Portuguese Merino sheep

BACKGROUND

Ovine footrot caused by Dichelobacter nodosus (D. nodosus) is a contagious disease with serious economic and welfare impacts in sheep production systems worldwide. A better understanding of the host genetic architecture regarding footrot resistance/susceptibility is crucial to develop disease control strategies that efficiently reduce infection and its severity. A genome-wide association study was performed using a customized SNP array (47,779 SNPs in total) to identify genetic variants associated to footrot resistance/susceptibility in two Portuguese native breeds, i.e. Merino Branco and Merino Preto, and a population of crossbred animals. A cohort of 1375 sheep sampled across 17 flocks, located in the Alentejo region (southern Portugal), was included in the analyses.

RESULTS

Phenotypes were scored from 0 (healthy) to 5 (severe footrot) based on visual inspection of feet lesions, following the Modified Egerton System. Using a linear mixed model approach, three SNPs located on chromosome 24 reached genome-wide significance after a Bonferroni correction (p < 0.05). Additionally, six genome-wide suggestive SNPs were identified each on chromosomes 2, 4, 7, 8, 9 and 15. The annotation and KEGG pathway analyses showed that these SNPs are located within regions of candidate genes such as the nonsense mediated mRNA decay associated PI3K related kinase (SMG1) (chromosome 24) and the RALY RNA binding protein like (RALYL) (chromosome 9), both involved in immunity, and the heparan sulfate proteoglycan 2 (HSPG2) (chromosome 2) and the Thrombospodin 1 (THBS1) (chromosome 7) implicated in tissue repair and wound healing processes.

CONCLUSION

This is the first attempt to identify molecular markers associated with footrot in Portuguese Merino sheep. These findings provide relevant information on a likely genetic association underlying footrot resistance/susceptibility and the potential candidate genes affecting this trait. Genetic selection strategies assisted on the information obtained from this study could enhance Merino sheep-breeding programs, in combination with farm management strategies, for a more effective and sustainable long-term solution for footrot control.

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.

Administration of Vaccines in Dairy Sheep and Goat Farms:Patterns of Vaccination, Associations with Health and Production Parameters, Predictors

This paper reports findings regarding patterns of vaccine usage in sheep and goat farms, in 325 sheep flocks and 119 goat herds throughout Greece. The objectives of the study were (a) to describe the patterns of vaccine administration in small ruminant farms and (b) to highlight factors that were associated with vaccinations in the farms. Vaccination against brucellosis was performed in all farms into the study. Among optional vaccinations, anti-clostridial vaccination was most frequently performed (in 97.8% of farms), followed by vaccination against contagious agalactia, (56.5% of farms), pneumonia (41.2%), chlamydial abortion (38.1%), staphylococcal mastitis (36.0%), and paratuberculosis (9.5%). Vaccinations against pneumonia and staphylococcal mastitis were performed more frequently in sheep flocks, whilst vaccinations against paratuberculosis were performed more frequently in goat herds. On average, 2.8 and 2.7 optional vaccinations (i.e., additionally to vaccination against brucellosis) were performed in sheep and goat farms, respectively. The increased number of vaccines administered was associated with a higher average milk production in the respective farms. There was an association of vaccination against staphylococcal mastitis with a reduced recovery of staphylococci from the bulk-tank raw milk. In multivariable analyses, significant associations of the administration of the various optional vaccines were seen with 15 variables, 11 related to health management practices and 4 related to the demographic characteristics of farmers; the collaboration with a veterinarian, the daily number of milking sessions, and the period spent daily by the farmer at the farm premises were each associated with the administration of vaccines against three infections.

Of herds and societies-Seasonal aspects of Vinča culture herding and land use practices revealed using sequential stable isotope analysis of animal teeth

Late Neolithic Vinča communities, spread over much of central and northern Balkans during the late sixth to mid-fifth millennium BC and characterised by unusually large and densely population centres, would have required highly organised food production systems. Zooarchaeological analysis indicates that domesticate livestock were herded, but little is known about the seasonal husbandry practices that helped ensure a steady supply of animal products to Vinča farming communities. Here, we present new stable carbon (δ13C) and oxygen (δ18O) isotopic measurements of incremental bioapatite samples from the teeth of domesticated livestock and wild herbivore teeth from two late Neolithic Vinča culture sites: Vinča-Belo brdo and Stubline (Serbia). Our results show a low variation overall within sheep and goats in terms of pasture type that may have been composed of seasonal halophyte plant communities, which have higher δ13C values due to the saline rich growing environments. Cattle feeding strategies were more variable and provided with supplementary forage, such as cut branches or leafy hay, during winter. The sharp distinction in the management of cattle and sheep/goat may be associated with the development of herding strategies that sought to balance livestock feeding behaviours with available forage or, more provocatively, the emergence of household-based control over cattle-an animal that held a central economic and symbolic role in Vinča societies.

Evaluation of Infrared Thermography for the Detection of Footrot and White Line Disease Lesions in Dairy Sheep

The objectives of this study were to investigate temperature distribution at the sheep hoof and evaluate the reliability and diagnostic performance of infrared thermography (IRT) for the detection of footrot and white line disease (WLD) lesions in intensively reared dairy sheep. Hoof lesions were clinically assessed, and IRT was used to measure temperature distribution on hoof superficial tissue in 600 multiparous ewes. Binary regression models were developed and validated, and receiver operating characteristic curves were estimated to assess the predictive value and diagnostic performance of IRT for the detection of hoof lesions. The most sensitive prediction model for the detection of IFR was based on the difference between ambient and hoof heel temperature (sensitivity: 83.3%, specificity: 47.8%, and threshold value: 6.5 °C), whereas the most specific prediction model was based on the difference between ambient and coronary band temperature (sensitivity: 51.9%, specificity: 79.7%, and threshold value: 11.3 °C). In the case of WLD, the diagnostic performance of IRT had limited predictive value. IRT could be a useful tool for hoof health screening in dairy sheep. However, it must be cautiously adapted in cases where environmental, operating, and operator variables are not effectively controlled.

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.

Ovine Footrot and Its Clinical Management

Footrot is one of the most important causes of lameness and economic losses in sheep and goat production worldwide. A 2-years-old ram was presented to the college of veterinary science teaching hospital, Mekelle University, with a history of non-weight bearing lameness of the left hindlimb. The hoof was damaged, split and the interdigital space was full of dirt and the scent of a rotten smell. On clinical examination, the sheep was suffering from depression, weight loss,  with elevation in the physiological parameters such as a rectal temperature of 40.1°C, heart rate of 96 beats per minute, and respiratory rate of 40 breaths per minute. The hoof was carefully washed with isotonic saline solution and disinfected with hydrogen peroxide 3% and povidone-iodine 1%. Additionally, meloxicam (0.5mg/kg, IM) thrice daily for three days and oxytetracycline 10% (10mg/kg, IM) for successive 5 days were administered parenterally. The infected surface was also treated with topical oxytetracycline spray for five days. The sheep have recovered after 7 days of treatment with significant improvement in the hoof injury. Successful management of footrot in Abergele sheep is discussed in the current case report.

Staphylococcus aureus in Agriculture: Lessons in Evolution from a Multispecies Pathogen

Staphylococcus aureus is a formidable bacterial pathogen that is responsible for infections in humans and various species of wild, companion, and agricultural animals. The ability of S. aureus to move between humans and livestock is due to specific characteristics of this bacterium as well as modern agricultural practices. Pathoadaptive clonal lineages of S. aureus have emerged and caused significant economic losses in the agricultural sector. While humans appear to be a primary reservoir for S. aureus, the continued expansion of the livestock industry, globalization, and ubiquitous use of antibiotics has increased the dissemination of pathoadaptive S. aureus in this environment. This review comprehensively summarizes the available literature on the epidemiology, pathophysiology, genomics, antibiotic resistance (ABR), and clinical manifestations of S. aureus infections in domesticated livestock. The availability of S. aureus whole-genome sequence data has provided insight into the mechanisms of host adaptation and host specificity. Several lineages of S. aureus are specifically adapted to a narrow host range on a short evolutionary time scale. However, on a longer evolutionary time scale, host-specific S. aureus has jumped the species barrier between livestock and humans in both directions several times. S. aureus illustrates how close contact between humans and animals in high-density environments can drive evolution. The use of antibiotics in agriculture also drives the emergence of antibiotic-resistant strains, making the possible emergence of human-adapted ABR strains from agricultural practices concerning. Addressing the concerns of ABR S. aureus, without negatively affecting agricultural productivity, is a challenging priority.

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 prevalence of Dichelobacter nodosus in clinically footrot-free sheep flocks: a comparative field study on elimination strategies

Background

Ovine footrot caused by Dichelobacter nodosus (D nodosus) is an infectious disease affecting sheep worldwide. Switzerland plans a nationwide footrot eradication program, based on PCR-testing of interdigital swab samples. The aim of this study was to test for the presence of D nodosus in clinically footrot-free sheep flocks which had been subjected to different treatment strategies, to assess whether they were feasible for the eradication process, especially focussing on antimicrobial flock treatments. Clinical scoring and PCR-results were compared. Ten farms had used hoof bathing and hoof trimming without causing bleeding, ten had used individual treatments and flock vaccines to gain the free status and ten had become free through whole-flock systemic macrolide treatment. For every farm, three risk-based collected pool samples were analysed for the occurrence of virulent and benign D nodosus by PCR detection of aprV2/aprB2.

Results

Six flocks from any treatment group tested positive for aprB2 in all pools. Clinical signs were absent at the time of sampling, but some flocks had experienced non-progressive interdigital inflammation previously. Two flocks tested aprV2-positive in the high-risk pool. One of them underwent a progressive footrot outbreak shortly after sampling. Individual retesting indicated, that virulent D nodosus most likely was reintroduced by a recently purchased ram. In the second flock, a ram was tested positive and treated before clinical signs occurred.

Conclusions

All treatment strategies eliminated the causative agent and were found to be suitable for implementation in the PCR-based eradication process. PCR-testing proved to be more sensitive than visual scoring, as it also detected clinically healthy carriers. It will be of benefit as a diagnostic tool in elimination and surveillance programs.

INTERDIGITAL NECROBACILLOSIS ASSOCIATED WITH TRUEPERELLA PYOGENES IN GOITERED GAZELLES ( GAZELLA SUBGUTTUROSA)

  This study presents the clinical findings, treatment results, and gross pathology of Trueperella pyogenes-associated interdigital necrobacillosis in captive goitered gazelles ( Gazella subgutturosa). Four male and two female gazelles presented with weight loss, front limb swelling, and persistent lameness despite antibiotic treatment. The animals were reluctant to bear weight on the affected limbs, and the diagnosis of interdigital necrobacillosis was made based on physical exam, bacteriologic evaluation, and radiographic imaging. In all cases, the interdigital skin and subcutaneous tissues were affected in both forelimbs. Exungulation (loss of the hoof) occurred in one female gazelle. Despite aggressive topical and systemic treatment, the two female gazelles died. Gross pathology detected abscesses in the heart, lung, and liver. T. pyogenes was isolated as the major pathogen. This is the first report of interdigital necrobacillosis caused by T. pyogenes in Gazella subgutturosa.

Aetiology, Risk Factors, Diagnosis and Control of Foot-Related Lameness in Dairy Sheep

During the last twenty years, considerable research efforts have recognized the consequences of foot-related lameness primarily in cattle, and meat and wool sheep. Despite the lack of extensive epidemiological studies, field observations and isolated research reports in dairy sheep have suggested that the problem might be more severe in semi-intensive and intensive farming systems. Footrot, contagious ovine digital dermatitis, ovine interdigital dermatitis, white line disease, and pedal joint abscess are the most common causes of foot-related lameness. Dichelobacter nodosus, Fusobacterium necrophorum, Treponema spp., and Actinomyces pyogenes are the most significant foot-related lameness-associated pathogens. Despite a documented hereditary predisposition, environmental factors are the most important in determining the occurrence of foot-related lameness. Moist and warm environment, increased parity and milk yield, inappropriate housing conditions and infrastructures, inadequate hygiene status, imbalanced nutrition, and insufficient foot care are the most critical risk factors. Furthermore, a foot-lameness control plan should include targeted implementation of claw trimming and footbathing, evidence-based planning of hygiene measures in preventive veterinary practices (i.e., antibiotic administration, vaccinations against footrot), selective breeding to footrot resistance, and, most importantly, the continuous training of farming personnel. Controlling foot-lameness in dairy sheep is critical in determining the well-being of animals, and strongly affects the farm's profitability and sustainability.

Influence of dietary zinc on the claw and interdigital skin of sheep

Claw diseases like interdigital dermatitis and footrot threaten sheep health and are major welfare issues. Several studies mainly done in cattle suggested that zinc (Zn) supplementation may improve claw integrity. However, Zn supplements may differ markedly regarding Zn bioavailability. Zn bound to single amino acids has been shown to be more bioavailable than inorganic Zn sources. The aim of this study was to determine the effect of different Zn supplements on the integrity of the claw and interdigital skin of healthy sheep. At weaning 30 Merino lambs were randomly allocated to three different dietary treatments which were provided through the pelleted concentrates as follows: 1) no supplemental Zn (Zn0); 2) addition of 40 mg/kg Zn as Zn sulphate (ZnS); 3) addition of 40 mg/kg organic Zn as Zn amino acid complex (CZn). Barley straw and pelleted concentrates were given ad-libitum. The calculated Zn concentration of the total diet (roughage and concentrate) without supplemental Zn (Zn0) was 38 mg Zn/kg DM. The concentrates were formulated to meet the nutritional requirements for growing lambs and contained 207 g/kg DM crude protein and 12.4 MJ/kg DM metabolizable energy. After 8 weeks the lambs were slaughtered and the following specimens were collected: blood serum, liver, sole and coronary band of the claw, and interdigital skin. Serum and tissue Zn and copper (Cu) concentrations and claw hardness were determined. Routine pathohistology and electron microscopy were conducted. Franz diffusion cell system and Ki-67 immunostaining were used to determine the permeability of the interdigital skin and the keratinocyte proliferation in the basal layer of sole horn, coronary band and interdigital skin, respectively. The concentrations of Zn and Cu in serum and liver tissue as well as the Zn concentration in claw horn were not affected by dietary treatment. Zn0 lambs showed higher (p < 0.05) Cu concentrations in claw horn compared to both Zn supplemented groups. Routine pathohistology as well as electron microscopy did not show significant morphological differences between the three groups. Franz diffusion cell system proved to be a suitable method examining the interdigital skin permeability, but the group differences in this study were not significant. Dietary treatment did not affect keratinocyte proliferation in the coronary band. In the sole keratinocyte proliferation was significantly higher (p < 0.05) in the Zn0 group compared to CZn with ZnS being intermediate. Keratinocyte proliferation in the interdigital skin was significantly higher (p < 0.05) in the CZn group compared to the Zn0 with ZnS being intermediate. The results of the current experiment indicate that serum and tissue Zn concentrations and horn hardness are not affected by adding a moderate amount of Zn sulphate or Zn amino acid complex to a basal diet. However, supplemental Zn amino acid complex seems to affect keratinocyte proliferation of interdigital skin and sole horn of lambs. Effects on skin permeability should be retested using a higher number of animals prospectively.

Sheep and farm level factors associated with footrot: a longitudinal repeated cross-sectional study of sheep on six farms in the UK

Footrot is an ovine foot disease of infectious origin and a cause of serious welfare and economic compromise in affected animals and flocks. The development of footrot in sheep is associated with the infectious agent Dichelobacter nodosus, which may invade as a primary pathogen, but the risk of disease is increased following damage to the interdigital skin of the foot. In this study, we used data from six farms in North Wales collected between June 2012 and October 2013 to model the dynamic changes of footrot prevalence over time and investigate the association of footrot with multiple farm, management, environmental and sheep factors. Footrot prevalence varied widely within and between farms and overall varied with season with an increase in prevalence shown in late summer and again in the spring. In addition, sheep were more likely to have footrot when the flock size was larger, when grazing poached pasture or when grazing a longer sward, and yearling sheep were less likely to have footrot when compared with lambs and adult sheep. These data may be helpful for advising farmers of likely environmental events, risk groups and management practices that may increase the probability of sheep developing footrot.

A genome-wide significant association on chromosome 2 for footrot resistance/susceptibility in Swiss White Alpine sheep

Footrot is one of the most important causes of lameness in global sheep populations and is characterized by a bacterial infection of the interdigital skin. As a multifactorial disease, its clinical representation depends not only on pathogen factors and environmental components but also on the individual resistance/susceptibility of the host. A genetic component has been shown in previous studies; however, so far no causative genetic variant influencing the risk of developing footrot has been identified. In this study, we genotyped 373 Swiss White Alpine sheep, using the ovine high-density 600k SNP chip, in order to run a DNA-based comparison of individuals with known clinical footrot status. We performed a case-control genome-wide association study, which revealed a genome-wide significant association for SNP rs418747104 on ovine chromosome 2 at 81.2 Mb. The three best associated SNP markers were located at the MPDZ gene, which codes for the multiple PDZ domain crumbs cell polarity complex component protein, also known as multi-PDZ domain protein 1 (MUPP1). This protein is possibly involved in maintaining the barrier function and integrity of tight junctions. Therefore, we speculate that individuals carrying MPDZ variants may differ in their footrot resistance/susceptibility due to modified horn and interdigital skin integrity. In conclusion, our study reveals that MPDZ might represent a functional candidate gene, and further research is needed to explore its role in footrot affected sheep.

A financial cost-benefit analysis of eradicating virulent footrot

In 2008, virulent footrot was detected in sheep in south-west Norway. Footrot is caused by Dichelobacter nodosus, and the outbreak was linked to live sheep imported from Denmark in 2005. A large-scale program for eradicating the disease was implemented as a joint industry and governmental driven eradication project in the years 2008-2014, and continued with surveillance and control measures by the Norwegian Food Safety Authority from 2015. The cost of the eradication program including surveillance and control measures until 2032 was assumed to reach approximately €10.8 million (NOK 90 million). A financial cost-benefit analysis, comparing costs in the eradication program with costs in two simulated scenarios, was carried out. In the scenarios, designated ModerateSpread (baseline) and SlowSpread, it was assumed that the sheep farmers would undertake some voluntary measures on their own that would slow the spread of the disease. The program obtained a positive NPV after approximately 12 years. In a stochastic analysis, the probabilities of a positive NPV were estimated to 1.000 and to 0.648 after 15 years and to 0.378 and 0.016 after ten years, for the ModerateSpread and SlowSpread scenarios respectively. A rapid start-up of the program soon after the detection of the disease was considered crucial for the economic success as the disease would have become more widespread and probably raised the costs considerably at a later start-up.

Sample pooling for real-time PCR detection and virulence determination of the footrot pathogen Dichelobacter nodosus

Dichelobacter nodosus is the principal cause of ovine footrot and strain virulence is an important factor in disease severity. Therefore, detection and virulence determination of D. nodosus is important for proper diagnosis of the disease. Today this is possible by real-time PCR analysis. Analysis of large numbers of samples is costly and laborious; therefore, pooling of individual samples is common in surveillance programs. However, pooling can reduce the sensitivity of the method. The aim of this study was to develop a pooling method for real-time PCR analysis that would allow sensitive detection and simultaneous virulence determination of D. nodosus. A total of 225 sheep from 17 flocks were sampled using ESwabs within the Swedish Footrot Control Program in 2014. Samples were first analysed individually and then in pools of five by real-time PCR assays targeting the 16S rRNA and aprV2/B2 genes of D. nodosus. Each pool consisted of four negative and one positive D. nodosus samples with varying amounts of the bacterium. In the individual analysis, 61 (27.1%) samples were positive in the 16S rRNA and the aprV2/B2 PCR assays and 164 (72.9%) samples were negative. All samples positive in the aprV2/B2 PCR-assay were of aprB2 variant. The pooled analysis showed that all 41 pools were also positive for D. nodosus 16S rRNA and the aprB2 variant. The diagnostic sensitivity for pooled and individual samples was therefore similar. Our method includes concentration of the bacteria before DNA-extraction. This may account for the maintenance of diagnostic sensitivity. Diagnostic sensitivity in the real-time PCR assays of the pooled samples were comparable to the sensitivity obtained for individually analysed samples. Even sub-clinical infections were able to be detected in the pooled PCR samples which is important for control of the disease. This method may therefore be implemented in footrot control programs where it can replace analysis of individual samples.

Cloning, Expression, and Functional Characterization of Serine Protease Aprv2 from Virulent Isolate Dichelobacter nodosus of Indian Origin

A gene encoding an extracellular protease from Dichelobacter nodosus was characterized and expressed in E. coli rosetta-gami (DE3). The nucleotide sequence analysis revealed an ORF of 1427 bp ecoding 475 amino acids long protein of calculated molecular weight 50.6 kDa and pI value 6.09. The phylogenetic analysis showed relatedness to subtilisin-like serine proteases of peptidase S8 family. The amino acid sequence analysis showed presence of N-terminal pre-peptide (1-23 aa), pro-peptide (24-160 aa), peptidase S8 domain (161-457 aa), and a C-terminal extension (458-475 aa). The gene harboring native signal peptide was expressed in pET-22b(+) for production of AprV2 recombinant protein. SDS-PAGE revealed the highest production of IPTG induced recombinant protein ∼37 kDa at 16 °C after 16 h. The purified protein after Ni-NTA affinity chromatography showed single protein band of ∼37 kDa which was also confirmed by the detection of blue coloured band of same size in Western blotting. The recombinant protein showed activity over broad temperature and pH range with optimum at 35 °C and pH 7.0. Similarly, the enzyme was stable over broad range 15-65 °C and 4-10 pH with maximum stability at 25 °C and pH 6. The activity of purified enzyme was also stimulated in the presence of Ca²⁺. The purified enzyme showed highest activity towards casein as compared to gelatin and BSA. These findings suggest AprV2 as an important candidate for industrial applications such as pharmaceuticals.

Characterisation of Dichelobacter nodosus and detection of Fusobacterium necrophorum and Treponema spp. in sheep with different clinical manifestations of footrot

The aim of this study was to determine the proportion of Dichelobacter nodosus, Fusobacterium necrophorum and Treponema spp. in sheep with different clinical manifestations of footrot compared to healthy sheep both at flock and individual level. The second aim was to characterise D. nodosus with respect to virulence, presence of intA gene and the serogroups. Swab samples (n=1000) from footrot-affected (n=10) and healthy flocks (n=10) were analysed for the presence of D. nodosus, F. necrophorum and Treponema spp. by real-time PCR and culturing (D. nodosus only). Dichelobacter nodosus isolates (n=78) and positive swabs (n=474) were analysed by real-time PCR for the aprV2/B2 and the intA genes and by PCR for the fimA gene (isolates only). D. nodosus was more commonly found in flocks affected with footrot than in clinically healthy flocks. A significant association was found between feet with severe footrot lesions and the aprV2 gene and between feet with moderate or no lesions and the aprB2 gene, respectively. F. necrophorum was more commonly found in flocks with footrot lesions than in flocks without lesions. No significant association was found between sheep flocks affected with footrot and findings of Treponema spp. or the intA gene. Benign D. nodosus of six different serogroups was detected in twelve flocks and virulent D. nodosus of serogroup G in one. In conclusion, D. nodosus and F. necrophorum were more commonly found in feet with footrot than in healthy feet. The majority of D. nodosus detected was benign, while virulent D. nodosus was only detected in a single flock.

Selenium supplementation restores innate and humoral immune responses in footrot-affected sheep

Dietary selenium (Se) alters whole-blood Se concentrations in sheep, dependent upon Se source and dosage administered, but little is known about effects on immune function. We used footrot (FR) as a disease model to test the effects of supranutritional Se supplementation on immune function. To determine the effect of Se-source (organic Se-yeast, inorganic Na-selenite or Na-selenate) and Se-dosage (1, 3, 5 times FDA-permitted level) on FR severity, 120 ewes with and 120 ewes without FR were drenched weekly for 62 weeks with different Se sources and dosages (30 ewes/treatment group). Innate immunity was evaluated after 62 weeks of supplementation by measuring neutrophil bacterial killing ability. Adaptive immune function was evaluated by immunizing sheep with keyhole limpet hemocyanin (KLH). The antibody titer and delayed-type hypersensitivity skin test to KLH were used to assess humoral immunity and cell-mediated immunity, respectively. At baseline, FR-affected ewes had lower whole-blood and serum-Se concentrations; this difference was not observed after Se supplementation. Se supplementation increased neutrophil bacterial killing percentages in FR-affected sheep to percentages observed in supplemented and non-supplemented healthy sheep. Similarly, Se supplementation increased KLH antibody titers in FR-affected sheep to titers observed in healthy sheep. FR-affected sheep demonstrated suppressed cell-mediated immunity at 24 hours after intradermal KLH challenge, although there was no improvement with Se supplementation. We did not consistently prevent nor improve recovery from FR over the 62 week Se-treatment period. In conclusion, Se supplementation does not prevent FR, but does restore innate and humoral immune functions negatively affected by FR.

Selenium supplementation alters gene expression profiles associated with innate immunity in whole-blood neutrophils of sheep

Footrot (FR) is a common, contagious bacterial disease of sheep that results in lameness and significant economic losses for producers. We previously reported that sheep affected with FR have lower whole-blood (WB) selenium (Se) concentrations and that Se supplementation in conjunction with routine control practices accelerates recovery from FR. To determine whether oral Se-yeast administered at supranutritional levels (>4.9 mg Se/week) alters the ability of sheep to resist or recover from FR infection, 60 ewes with and 60 ewes without FR were drenched once weekly for 62.5 weeks with 0, 4.9, 14.7, or 24.5 mg organic Se-yeast (30 ewes per treatment group). Footrot prevalence and severity were measured at 0, 20, 28, 40, and 60 weeks of Se supplementation. Genomic expression of eight WB-neutrophil genes for selenoproteins and seven WB-neutrophil genes for proteins involved in innate immunity was determined at the end of the treatment period using SYBR Green and quantitative polymerase chain reaction methodology. Supranutritional Se-yeast supplementation successfully increased Se status in sheep but did not prevent FR. Supranutritional Se-yeast supplementation increased WB-neutrophil expression of genes involved in innate immunity: L-selectin, interleukin-8 receptor, and toll-like receptor 4, which were or tended to be lower in ewes affected with FR. Furthermore, supranutritional Se-yeast supplementation altered the expression of selenoprotein genes involved in innate immunity, increasing selenoprotein S and glutathione peroxidase 4 and decreasing iodothyronine deiodinases 2 and 3. In conclusion, supranutritional Se-yeast supplementation does not prevent FR, but does alter WB-neutrophil gene expression profiles associated with innate immunity, including reversing those impacted by FR.

Development and comparison of a real-time PCR assay for detection of Dichelobacter nodosus with culturing and conventional PCR: harmonisation between three laboratories

Background

Ovine footrot is a contagious disease with worldwide occurrence in sheep. The main causative agent is the fastidious bacterium Dichelobacter nodosus. In Scandinavia, footrot was first diagnosed in Sweden in 2004 and later also in Norway and Denmark. Clinical examination of sheep feet is fundamental to diagnosis of footrot, but D. nodosus should also be detected to confirm the diagnosis. PCR-based detection using conventional PCR has been used at our institutes, but the method was laborious and there was a need for a faster, easier-to-interpret method. The aim of this study was to develop a TaqMan-based real-time PCR assay for detection of D. nodosus and to compare its performance with culturing and conventional PCR.

Methods

A D. nodosus-specific TaqMan based real-time PCR assay targeting the 16S rRNA gene was designed. The inclusivity and exclusivity (specificity) of the assay was tested using 55 bacterial and two fungal strains. To evaluate the sensitivity and harmonisation of results between different laboratories, aliquots of a single DNA preparation were analysed at three Scandinavian laboratories. The developed real-time PCR assay was compared to culturing by analysing 126 samples, and to a conventional PCR method by analysing 224 samples. A selection of PCR-products was cloned and sequenced in order to verify that they had been identified correctly.

Results

The developed assay had a detection limit of 3.9 fg of D. nodosus genomic DNA. This result was obtained at all three laboratories and corresponds to approximately three copies of the D. nodosus genome per reaction. The assay showed 100% inclusivity and 100% exclusivity for the strains tested. The real-time PCR assay found 54.8% more positive samples than by culturing and 8% more than conventional PCR.

Conclusions

The developed real-time PCR assay has good specificity and sensitivity for detection of D. nodosus, and the results are easy to interpret. The method is less time-consuming than either culturing or conventional PCR.