Persistence of Dichelobacter nodosus, the causal agent of ovine footrot

Watson, Katharina, Green, L and Purdy, K (2017) Persistence of Dichelobacter nodosus, the causal agent of ovine footrot. In: Proceedings of the British Society of Animal Science Annual Conference: The future of Animal Science. Advances in Animal Biosciences, 26th - 27th April 2017, Chester.

Text BSAS_2017_-_Proceedings.pdf - Published Version Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (4MB)

Abstract

Application Ovine footrot is the main cause of lameness in sheep in the UK. Information on sites where the causative agent of footrot Dichelobacter nodosus persists may lead to changes in sheep management and disease control. Introduction Ovine footrot (FR) is an economically important disease that causes lameness and affects sheep flocks worldwide. It is characterized by interdigital skin inflammation (interdigital dermatitis [ID]) with, or without, separation of the hoof horn from the underlying tissue (severe footrot [SFR]). The primary causative agent is the gram-negative anaerobic bacterium Dichelobacter nodosus, which is thought to exclusively colonize the hoof and is transmitted indirectly via contaminated surfaces. Periods of apparent zero prevalence of FR in a flock are followed by disease occurrence when climatic conditions become favourable for pathogen transmission. This suggests that there are sites were D.nodosus persists. These sites might include the feet, gingival cavity and faeces of sheep and the environment. The aim of this study was to investigate persistence of D. nodosus, by investigating possible sites of survival, using a longitudinal study design. Materials and methods Study 1: From a flock of approximately 150 animals, 5 North Country Mules and 5 lambs (Northcountry mule x Texel) were selected for the study. All animals and their pasture were examined and sampled (including swabs from feet and the gingival cavity, as well as soil, grass and faecal samples) fortnightly from June to August for a period of 8 weeks. Study 2: A flock of 120 Suffolk x Wiltshire-horn ewe lambs was screened for FR and 40 animals without FR lesions were selected randomly and moved to a study pasture that had been unoccupied for 10 days. The study group and pasture were examined and sampled weekly for five months from January to May. For both studies, sheep were turned and scored for ID and SFR lesions using a 4-point scale (Moore, et al., 2005). Swabs were taken from the interdigital skin of the foot (study 1: n=40, study 2: n=160) and from the gingival cavity (study 1: n=10, study 2: n=40) at every visit. Faecal samples (n=10) were collected from the pasture (study 1 only). For study 2 faecal samples (n=40) were taken directly from the animal. Soil samples (n=22) were collected weekly and grass samples were taken when present at these sites (n=6). Local climate data (ambient temperature [°C] and rainfall [mm]) was collected. All samples from study 1 were analysed resulting in a total of 342 samples. For study 2, DNA was extracted from 7 sheep (5 sheep with footrot lesions and 2 control sheep with no disease), and all samples collected from the pasture; a total of 898 samples. Real-time PCR used to detect and quantify D.nodosus. Chi square tests using R software were used for the preliminary statistical analysis. Results Flock disease prevalence was higher in study 1 than in study 2. The climate during study 1 was warm and initially wet, but became progressively drier and the climate during study 2 was cold and dry. D. nodosus was detected in all sample types in both studies but not on all occasions (Table 1). Detection levels differed significantly between the two studies in feet, gingival cavity, soil, and grass samples (P<0.01). The proportion of positive foot swabs was greater than expected by chance (P<0.01) in both studies. The proportion of positive faecal samples (study 1) and grass samples (study 2) was lower than expected by chance (P<0.05). Conclusions For the first time we show that D. nodosus can be shed in ovine faeces. The differences in detection between studies are likely to be attributable to differences in disease status of the study groups and climatic conditions. D. nodosus was detected in all sample types in both studies but was less prevalent in non-foot sites, especially when the weather was dry, suggesting that feet are the more likely place of persistence. A binomial mixed regression model will be used to further elucidate variables temporally associated with the presence of D. nodosus in feet, in the gingival cavity and on the pasture.

Item Type:	Conference or Workshop Item (Paper)
Divisions:	Agriculture, Science and Practice
Depositing User:	Dr Katharina Watson
Date Deposited:	04 Apr 2025 14:25
Last Modified:	04 Apr 2025 14:25
URI:	https://rau.repository.guildhe.ac.uk/id/eprint/16949

Actions (login required)

Edit Item