Unravelling the aetiology of contagious ovine digital dermatitis.

Contagious ovine digital dermatitis (CODD) is an extremely severe and relatively recent cause of infectious lameness in sheep in the UK, affecting approximately 35-53% of UK sheep farms and 300,000 sheep annually. The economic impact of CODD is unknown but likely similar to that of footrot, another common cause of lameness which is estimated at £24million per year. The Farm Animal Welfare Council, who report to the UK government on farm animal welfare issues, identified that research into this new disease should be a priority. Research into footrot has led to substantial improvements for the evidenced based advice available to farmers and vets on this aspect of lameness, and has been widely taken up by the sheep industry. However many farmers are struggling to control CODD infection in their flocks and substantial research support is required here.
The applicants are currently the only research group studying CODD and through funding from the British Veterinary Association, HCC and EBLEX, this research group is making advances in our understanding of the epidemiology, pathology and microbiology of the disease, including the development of control strategies using antimicrobial drugs. The outputs of this work will produce practical solutions for the farming industry. Given the severe pressure on antimicrobial usage world-wide, sustainable, non-antibiotic solutions to CODD must focus on preventative approaches such as stopping the introduction of disease into naïve flocks through biosecurity and improvement in the sheep's ability to resist infection through vaccination. Both these solutions require a greater knowledge of the agent(s) causing the disease than we currently possess.
We have already demonstrated evidence that specific culturable treponemes identical to those from bovine digital dermatitis have an association with CODD lesions and data from other studies has suggested a role for Dichelobacter nodosus and Fusobacterium necrophorum. This study proposes to i) carry out substantial metagenomic (entire microbial community) investigations of CODD lesions to identify the key microbes involved and ii)to characterise the host immune response to the identified microbes and determine whether specific antigens may allow a protective immune response to underpin future vaccine studies and iii) to use additional metagenomic surveys of the host farm environment and faeces to detect the relevant microbes which should allow for relevant farmer / veterinary guidelines to improve disease control.
This proposal would ensure we obtain a greater understanding of the role of different bacteria in CODD development. This information will be key to future vaccine studies so that the correct microorganisms are targeted for vaccine design. Monitoring specific immunity in the naive sheep flock to be used in this study after exposure to CODD will allow assessment of the different stages of the infective process. This will not only describe stages of microbial infections but may also identify whether some animals are able to produce an effective immune response allowing for subsequent antigen discovery for effective vaccines. Identification of the considered causal microorganisms will also allow for more appropriate antimicrobial treatments thus reducing the risk of antibiotic resistance developing. Monitoring bacterial populations of CODD lesions post treatment should inform biosecurity practices i.e. whether treated animals result in bacteriological cure or become asymptomatic CODD "carriers". Monitoring faeces and environmental samples prior and post antibiotic treatment will also allow for development of best farm practices to minimise reinfection of sheep with CODD thus preventing failure / overuse of antibiotic treatment at the flock level.
Investigating CODD using the various methods described above, should improve understanding of the disease and contribute towards the eradication of this painful and expensive disease.

Objectives:
Monitor by lesion and mobility score, pathogen qPCR and microbial metagenomics of foot swabs, host antibody and T cell responses; the transmission of CODD under experimental conditions between symptomatic (n=5) and naive sheep (n=20), pre (2 weeks) and post introduction (5 months) of CODD sheep and post antibiotic treatment (6 weeks).
Collect tissue biopsies from 6 CODD lesion stages (n=8 for each) from sheep on CODD endemic farms. Stages including 4 clinical disease stages, asymptomatic animals and 6 weeks post antibiotic treatment. Develop qPCR assays for previously identified pathogens and survey all aforementioned swab and tissue samples.
Evaluate temporal changes to ovine foot metagenome throughout the development of CODD to identify key associated pathogens by using shotgun metagenomic analysis of CODD lesions (tissues n=24 and swabs n=24 including above 6 lesion stages) and 16S rRNA gene targeted metagenomic analysis (tissues n=48 and swabs n=48 again of the above 6 lesion stages). Develop qPCR assays of metagenomic identified pathogens to subject all samples to and carry out retrospective isolations.
Characterise sheep immune responses, against metagenomic identified pathogens, from the experimental CODD outbreak to identify any protective immune responses and their associated antigens including specific classes of antibodies (IgG1, IgG2 and IgM), using both ELISA and western blotting and Th1 cell responses after co-incubating microbial antigen preparations with blood PBMCs of sheep healthy before exposure, active CODD lesion, resolving lesion and healthy at end of study (n=5 for each) using ELISA to determine secreted IFNg and IL-2.
To investigate the host environment and faeces (collected weekly in above CODD experimental study) for presence of disease associated micro-organisms during the experimental CODD outbreak using the developed qPCR assays and 16S rRNA gene targeted metagenomic analysis of faeces (n=30) and environment (n=28).

Contagious ovine digital dermatitis (CODD) is an endemic infectious disease causing lameness in sheep across the UK and Republic of Ireland (RoI) and is very important as it is extremely painful for animals involved. CODD is reported as more severe and at a similar prevalence to footrot suggesting >£24M per year losses to the UK sheep industry due to lost production, control measures and treatment. Reports identify 35-53% of UK sheep flocks as CODD affected with 2.0-2.4% morbidity on farm suggesting a large number of animals suffer in the UK alone (~300,000 per year of 30M UK sheep). The major benefactors of this research would be sheep as results produced could aid in eradicating or controlling CODD in turn preventing the suffering for hundreds of thousands of UK animals with an even greater impact when considering RoI is endemic and recent reports from South America and Europe. As similar manifestations have been reported in USA Wild Elk and UK Dairy Goats, CODD appears to be emerging into new hosts and this research should lead to better animal welfare for these also.
The general public worldwide and especially in UK would benefit from this research if new vaccines or effective control measures are identified as there would be reduced cost of sheep products and therefore a better standard of living. Currently, CODD has significant negative financial outcomes due to increased hoof inspection, veterinary fees, expensive (ineffective) treatments and weight gain reduction. Farmers would benefit as this is a costly disease in terms of time and finances. Prevention or eradication of this disease would have a positive effect on farm economics especially across the UK (& potentially worldwide).
There would also be environmental impact if CODD is eradicated/better controlled as a result of this research. Such strategies would reduce the need for footbaths and over-use of antibiotics. Footbath chemicals can be very environmentally damaging. Furthermore, overuse of antibiotics (especially ineffective ones used in footbaths) may induce antibiotic resistance in causative bacteria and other host/environment microbes, which could be damaging to the food chain.
The commercial sector will benefit from this research as this project will place in the public domain information to underpin novel treatments, control measures or identify all causal bacteria needed for efficacious vaccines. Once we identify relevant microbes for vaccines and potential control measures from environmental/faeces studies we will approach relevant companies as well as work closely with the project partners EBLEX and HCC whose job it is to produce guidelines for vets and farmers. If CODD control strategies identified are more widely applicable to other diseases then we will contact industry directly or form relationships with relevant academic groups to further investigate.
Towards realistic timescales for benefits to be realised from this grant, it could be considered completion of this work will have contributed to substantially underpinning future vaccine design and control methods. Therefore at the end of the grant (3 years) an industrial concern should then be able to use information produced to develop an effective vaccine or treatment within another 3-4 years whilst any farm management control measures could be delivered in terms of control guidelines immediately.
Project staff will develop comprehensive knowledge of metagenomics, infectious diseases and identifying vaccine candidates/control measures. These would benefit both researcher and applicants giving them skills useful to academia and industry. By having research dedicated CODD staff at the University of Liverpool we can support UK biotech companies better, for example we have previously shared culturing skills with a vaccine producer. Continuation of such activity is helped greatly by having a larger staff base and can only be good for the UK economy and increase its global economic performance.