Preventing contagious ovine digital dermatitis: Characterisation of bacterial pathogens and development of disease control measures to prevent transmi

Contagious ovine digital dermatitis (CODD) is a severe cause of sheep lameness. It affects approximately half of UK sheep flocks, and is emerging globally. Due to its' severity, CODD has a substantial and highly visible impact on sheep welfare. The economic consequences, and high levels of antibiotic use associated with disease control, negatively affect sustainability. In the 2021 Ruminant Health and Welfare Group survey of UK livestock farmers, CODD was a top priority endemic disease for the livestock industry; whilst recent surveys identified that improved understanding of disease transmission and prevention methods were farmers and vets top CODD research priorities.
The aim of this study is to inform and devise biosecurity protocols for prevention of between and within farm transmission of CODD.
Objective 1: Comparison, characterisation and localisation of pathogenic bacterial populations from field cases of footrot and CODD.
Evidence from experimental studies demonstrated that CODD occurs as a result of superinfection of pre-existing footrot lesions with three treponeme bacteria; Treponema medium, Treponema phagedenis and Treponema pedis (DD treponemes). To inform disease prevention on farms, this requires field validation. Therefore, we will compare the microbiomes, the presence, abundance and virulence characteristics of these DD treponeme bacteria from field cases of CODD and footrot using 16 S metagenomic analysis and quantitative PCR. Pathogen load and localisation will be studied using fluorescence in situ hybridisation.
Objective 2: Whole genome sequencing of T.medium, T.phagedenis, T.pedis isolates from cattle and sheep digital dermatitis lesions.
It is a long-held concern that the DD treponemes originated from bovine digital dermatitis (BDD), and that transmission between species occurs through the farm environment. This risks introduction of disease to naïve farms and maybe a source of infection in endemically affected farms. We will investigate this hypothesis using whole genome typing of T.medium, T.phagedenis and T.pedis isolates from farms affected by both BDD and CODD. We will also investigate their bacterial diversity and virulence factors.
Objective 3: Evaluate disinfection protocols for the elimination of CODD pathogens from sheep's feet.
As CODD continues to spread it is evident that current biosecurity advice is inadequate. We will conduct farm RCT trials to investigate the efficacy of disinfection protocols for the elimination of the CODD pathogens from sheep's feet. The protocols will be based on evidence gathered from the current study and pilot in vivo and in vitro efficacy data. Clinical examination, bacterial culture and qPCR will be used to assess efficacy.