Histopathological Characterization of the Lesions of Contagious Ovine Digital Dermatitis and Immunolabelling of Treponema-like Organisms

Abstract

Contagious ovine digital dermatitis (CODD) is a cause of severe lameness in sheep and the three Treponema phylogroups Treponema medium/Treponema vincentii-like, Treponema phagedenis-like and Treponema pedis have been associated with clinical disease. The aims of this study were: (1) to describe the histopathological changes associated with each previously established grade of clinical lesion, and (2) to investigate immunohistochemically the association of the Treponema-like organisms with the observed histopathological changes. Early lesions were characterized by lymphoplasmacytic infiltration of the distal digital skin, with suppurative coronitis and intracorneal pustules. In more advanced stages of the disease there was complete separation of the dorsal wall of the hoof with a necrotizing and fibrinosuppurative exudate and dermatitis. The later lesions were mostly resolved, but with milder suppurative changes remaining within the cornified layer and periosteal reaction of the dorsal aspect of the distal phalanx. Large numbers of Treponema-like organisms were identified within early grade lesions (as well as later, more advanced grade lesions) and were specifically associated with the observed histopathological changes. The results of this study provide some evidence in support of the hypothesis that the three CODD-associated Treponema phylogroups are involved in the aetiopathogenesis of this disease.

Keywords: Treponema; contagious ovine digital dermatitis; histopathology; sheep.