Contagious Ovine Digital Dermatitis: A Novel Bacterial Etiology and Lesion Pathogenesis.

Gareth J Staton,Simon R Clegg,Nicholas J Evans,Stuart D Carter,Dai Grove-White,Joseph W Angell,Jennifer S Duncan

doi:10.3389/fvets.2021.722461

Gareth J Staton, Simon R Clegg + Show 5 more

Open Access

https://doi.org/10.3389/fvets.2021.722461

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Abstract

Contagious ovine digital dermatitis (CODD) is a severe and common infectious foot disease of sheep and a significant animal welfare issue for the sheep industry in the UK and some European countries. The etiology and pathogenesis of the disease are incompletely understood. In this longitudinal, experimental study, CODD was induced in 18 sheep, and for the first time, the clinical lesion development and associated microbiological changes in CODD affected feet are described over time, resulting in a completely new understanding of the etiopathogenesis of CODD. The majority of CODD lesions (83.9%) arose from pre-existing interdigital dermatitis (ID) and/or footrot (FR) lesions. All stages of foot disease were associated with high levels of poly-bacterial colonization with five pathogens, which were detected by quantitative PCR (qPCR): Treponema medium, Treponema phagedenis, Treponema pedis, Dichelobacter nodosus, and Fusobacterium necrophorum. Temporal colonization patterns showed a trend for early colonization by T. phagedenis, followed by F. necrophorum and D. nodosus, T. medium, and then T. pedis, D. nodosus was present at significantly higher predicted mean log10 genome copy numbers in FR lesions compared to both ID and CODD, while Treponema species were significantly higher in CODD and FR lesions compared to ID lesions (p < 0.001). Treatment of CODD-affected sheep with two doses of 10 mg/kg long acting amoxicillin resulted in a 91.7% clinical cure rate by 3 weeks post-treatment; however, a bacteriological cure was not established for all CODD-affected feet. The study found that in an infected flock, healthy feet, healed CODD feet, and treated CODD feet can be colonized by some or all of the five pathogens associated with CODD and therefore could be a source of continued infection in flocks. The study is an experimental study, and the findings require validation in field CODD cases. However, it does provide a new understanding of the etiopathogenesis of CODD and further supportive evidence for the importance of current advice on the control of CODD; namely, ensuring optimum flock control of footrot and prompt isolation and effective treatment of clinical cases.

Highlights

Contagious ovine digital dermatitis (CODD) is a relatively new infectious foot disease of sheep, first recorded in the UK in 1997 [1]
This study presents a new understanding of the etiopathogenesis CODD in sheep, whereby the majority of CODD lesions developed from pre-existing interdigital dermatitis (ID)/and or FR lesions
CODD has a polymicrobial etiology associated with infection with the bacteria T. medium, T. phagedenis, T. pedis, D. nodosus, and F. necrophorum

Summary

Introduction

Contagious ovine digital dermatitis (CODD) is a relatively new infectious foot disease of sheep, first recorded in the UK in 1997 [1]. It is widespread in the UK, affecting an estimated 35– 58% of sheep flocks [2, 3] and has been reported in Ireland [4], Germany [5], and Sweden (personal comm.). The severity of lameness in CODD-affected sheep is a consequence of the extensive foot pathology caused by the disease (Figure 1). Histopathological examinations of early stage lesions are described as lymphoplasmacytic infiltration of the distal digital skin with suppurative coronitis and intracorneal pustules; in the more advanced stages of disease, there is complete separation of the dorsal wall of the hoof with a necrotizing and fibrinosuppurative exudate and dermatitis [8]

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