Understanding inflammatory processes in ovine footrot to inform rational vaccine design

Footrot is one of the most important diseases affecting the health and welfare of sheep in the UK and throughout the world, and impacts on productivity and profitability within the sheep industry. It is in the top five most important diseases of sheep and globally affects the income of the poorest farmers. Approximately 14 million sheep get footrot in the UK each year.
Footrot is caused by bacteria that invade the skin of the foot, and cause pain and swelling. In severe cases, the hoof horn capsule, the hard outer surface of the foot, separates from the underlying and sensitive living tissue, rather like a fingernail coming away from the finger. Affected sheep can be treated with an antibiotic injection, however to do this sheep have to be caught. Sheep are fearful animals and are very stressed by being caught and handled, so although it is good for their health and welfare to be treated, the very act of catching them to administer the treatment also reduces their welfare; 14 million treatments means a lot of very stressed sheep. If sheep are left untreated they lose weight, remain lame for some time and are less likely to become pregnant. If they do have lambs they produce less milk and so cannot feed their lambs as well as those ewes that are not lame, as well as impacting on their profitability.
We know that treatment by antibiotic injection early in disease leads to dramatic recovery within a few days. In the long term however, we want to stop using antibiotics to treat farm animals so that we reduce the risk of antibiotic resistance and avoid antibiotics being present in livestock farmed for human consumption. In addition, we want to reduce stress in sheep and avoid the need to catch and treat lame sheep. Ideally, rather that treating disease, we would prefer to prevent disease by vaccination. There is a vaccine available to assist in control of footrot, but less than 10% of UK farmers use this vaccine: it is neither long lasting (5 months maximum) nor very effective (60% effective at best). This lack of effectiveness is thought to be due to a failure to stimulate the best possible host immune response. Our research will help us to understand how sheep respond to the bacteria that cause footrot during the very early stages of infection, and will ultimately help in the development of alternative approaches to preventing disease, including a new vaccine in the longer term.
We will do this by studying the local immune defences in the sheep foot, how the bacteria causing footrot are recognised by the immune system and the immune response to these bacteria. In addition, we will investigate the relationships between individual strains of the bacterium that causes disease and the potential for certain strains to be associated with disease. We think that footrot might occur when the sheep immune system responds too much to the bacteria, rather like human intolerance to milk, when our gut reacts to milk proteins when it should not. Alternatively, this could be due to lack of regulation of the inflammatory response leading to excessive collateral damage to the surrounding tissues. If we are right, then this will explain why antibiotics are so good at aiding recovery from footrot - because they kill the bacteria and so reduce the sheep immune response. We will be able to see this by studying tissue samples taken from the feet of sheep affected and unaffected with footrot. We will also use tissue samples taken from healthy sheep that we will culture in the laboratory and expose to bacteria that cause footrot.
By the end of this project we will be able to explain better how the clinical signs of footrot are caused and how the immune system contributes to this. This will help to inform on new approaches to disease management and ultimately disease prevention.

The aetiology of footrot is complex and multifactorial. Physical damage to the interdigital skin is required to initiate disease following exposure to damp conditions. The incidence of footrot could therefore increase in line with the climate change predictions of warmer and wetter summers in the UK. Bacterial replication in the damaged skin leads to interdigital dermatitis where the superficial epidermal layers are inflamed, damaged and slough off. This can progress to footrot with separation of the hoof horn from the underlying tissue. The essential bacterium causing footrot is Dichelobacter nodosus. However, the role of a second bacterium, Fusobacterium necrophorum, in the pathogenesis of footrot is unclear. The host response to the invasion of bacteria is characterised by inflammation of the epidermis and pressure in the hoof horn capsule. Consequently the hoof horn separates from the underlying tissue. The host immune response is a double-edged sword, while it is required for successful defence, if unbalanced it can lead to pathology. Given that separation of the hoof horn is characterised by immune-mediated inflammation, investigating how this is initiated and controlled will dramatically improve our understanding of footrot pathogenesis. Analysing the global host immune response to footrot-associated bacteria is a first step in understanding local inflammation. Together with an insight into the molecular epidemiology of D. nodosus and analysis of the correlation of sequence type with disease presentation, this will greatly enhance our understanding of the aetiology of footrot.
This proposal will help to inform the design and delivery of novel therapeutic and vaccine approaches, with the ultimate aim of facilitating strategic effective vaccine development. This proposal aligns with solutions to food security, reducing antibiotic usage in meat production and the potential for resistance, and providing a sustainable, secure supply of good quality food.

Footrot is a bacterial infection of the interdigital skin of the sheep foot resulting in lameness, and is the greatest welfare and economic concern for sheep farmers and veterinarians worldwide. In England, more than 95% of sheep flocks have footrot, with a mean daily prevalence of ~10% and an estimated cost to the UK sheep industry of £24-84 million per annum. The results from this project will help to improve our understanding and management of footrot, a disease that impacts this industry and those concerned with animal welfare. It is therefore of relevance to the sheep industry (both pedigree and commercial sheep farmers), their consultants including veterinarians and policy makers, Farm Animal Welfare Committee and the RSPCA. We will ensure that our work has high visibility through peer-reviewed publications, trade publications and through presentations at scientific, veterinary and farmer meetings. We will continue work with EBLEX, the levy body for beef and sheep farmers, and transfer knowledge as appropriate throughout the project allowing interaction and promotion of results to key stakeholders. The results are also of potentially high media interest and could lead to a radical change in the approach to managing the foot health of sheep. The farming press (Farming Today, Farmer's Weekly) are routes to communicating the outputs of this project to the farming industry. In addition, outcomes will inform teaching practice and have the potential to change prevention and treatment of footrot.
This is a collaborative, multidisciplinary project and we envisage that the proposed research will benefit a wide range of academics working in diverse fields. It will benefit immunologists studying innate immunity to bacterial infections by elucidating host recognition and signalling responses to bacteria in a farm animal species of veterinary importance. It will also provide valuable tools (ovine TLR expression constructs, ovine skin fibroblast cell lines) to study other host - microbe interactions in sheep. This research will be of interest to scientists studying mechanisms of inflammation and immunopathology in response to infections. The generated and freely available mammalian transcriptome and pathogen genome and community profiling data will benefit the research community for diverse future research. In addition, the MLST analysis is a web based portable system that will allow others to 'plug and play' with their own data, thus developing an ever growing database of such information on D. nodosus globally, enabling bespoke global adaptation of project findings.
The public have a strong interest in the health and welfare of animals that are farmed for human consumption. This includes concerns over the use of antibiotics to control disease in food animals and the impact of disease on productivity that ultimately influences the quality and purchase cost of meat. Footrot in sheep impacts on all of these areas and is therefore pertinent to the global Food Security agenda. The applicants have expertise in communicating their science to broad audiences beyond the academic arena. Drs Tötemeyer and Coffey are involved in outreach activities including Science Week, Sutton Trust Summer Schools and as STEM ambassadors aiming to communicate veterinary science to pupils, including pupils from widening participation backgrounds. Dr Tötemeyer also reviewed for the Wikivet project. Prof Entrican and Dr Wattegedera have communicated their science to farmers at The Royal Highland Show and open days at Moredun Research Institute. They have presented to the public at The Edinburgh International Science Festival and have delivered immunology workshops to school teachers addressing the learning objectives relating to immunology and infectious disease within the new Curriculum for Excellence.