The epidemiology of ovine footrot and virulence and phylogeny of Dichelobacter nodosus in a single flock and globally

Footrot, caused by Dichelobacter nodosus, accounts for 70% of foot lesions in sheep in the UK and is a huge economic issue for the sheep industry. There are two clinical presentations: interdigital dermatitis and severe footrot where hoof horn separates from the underlying tissue. Neither D. nodosus load in relation to the severity within ID and SFR, nor the effects of footrot treatments on D. nodosus load, have been investigated. The phylogenetic diversity of D. nodosus and its key virulence factors also required deeper investigation as their association with clinical disease remain unclear. D. nodosus load was investigated using molecular techniques, on the feet of 99 ewes from one farm in the UK. Each ewe was assigned one of two treatments; foot trimming plus topical antibiotics or parenteral plus topical antibiotics. Interdigital skin swabs of two feet of 25 of the ewes were analysed and D. nodosus load quantified using qPCR. Fimbrial serogroup and acidic protease B2/V2 of D. nodosus were investigated through molecular and sequencing analysis. D. nodosus phylogeny was analysed at a single farm level and global level. D. nodosus load increased with ID score but showed no relationship with SFR score. D. nodosus load decreased one week after treatment with either FTA or PTA, but not with parenteral antibiotics alone (administered for a separate health reason). This indicates that topical antibiotics reduced D. nodosus load on feet. D. nodosus detection, along with fimbrial serogroup and acidic protease B2/V2 detection, was higher and more representative through molecular analysis than through culture. One of the three phylogenetic clades identified from the single farm data indicated that strain introduction occurred when new stock was brought onto the farm. From both the single farm data and global data, neither fimbrial serogroup nor acidic protease identification related to disease severity or pathogenicity