Application of 16S rRNA gene amplicon sequencing in the investigation of novel ovine skin lesions in Norway

Background Contagious ovine digital dermatitis (CODD) is a globally emerging polymicrobial foot disease in sheep that causes severe welfare and economic problems. Currently, there is no validated commercial laboratory diagnostic test for CODD, and the current ‘gold standard’ is the pathological scoring of foot lesions. In this study, we used a combination of gross pathological lesion scoring and 16S rRNA gene amplicon sequencing of the bacterial microbiome to investigate novel suspected CODD foot lesions identified in three Norwegian abattoirs. Methods We conducted 16S rRNA gene amplicon sequencing of biopsy samples from novel Norwegian foot lesions ( n = 30), footrot lesions ( n = 7), and healthy skin ( n = 30), and the results were compared with sequenced biopsy samples from a previous study of sheep from the United Kingdom (UK) with CODD lesions ( n = 31) and healthy foot skin ( n = 7). A UK veterinarian with clinical experience in CODD performed the pathological scoring of the novel Norwegian foot lesions using photographic images collected at the Norwegian abattoirs. Results Gross pathology and bacterial microbiome compositional analysis revealed that the novel CODD-like lesions were pathologically and bacteriologically distinct from healthy skin, CODD lesions, and footrot lesions. The novel CODD-like lesions presented as ulceration in the skin region immediately dorsal to the coronary band, extending distally below the carpus/tarsus, and were associated with hair loss, haemorrhage, and crusting. A comparison of the bacterial microbiota in the novel CODD-like lesions with those found in healthy skin, CODD lesions, and footrot lesions revealed that the bacterial communities were significantly different in terms of diversity, phylogeny, and microbial composition. Conclusion Gross pathological lesion description, used in combination with 16S rRNA gene sequencing of the bacterial microbiome, demonstrated that the novel Norwegian skin lesions involved a dysbiosis that differed substantially from what has been previously described for CODD lesions and that the lesions were highly unlikely to be CODD. Further studies on the aetiopathogenesis of this novel sheep hoof condition should enable improved diagnosis.