Footrot is an infectious bacterial disease of sheep which causes separation of the hoof from underlying soft tissues, leading to pain and lameness. This disease has major welfare and economic impacts on the sheep industry worldwide. The disease process for footrot is multifactorial and initiated by initial damage of the epidermis and mixed bacterial infection including Fusobacterium necrophorum allowing subsequent invasion by Dichelobacter nodosus. The description of the disease state can be split based on the gross pathology into the milder inter digital dermatitis (ID) and the more severe footrot.
The aim of this study is to investigate the host responses that occur during ID and footrot and to develop a robust histopathological scoring system that can be used to correlate host responses with disease severity and the extent of bacterial infection.
Skin hoof interface biopsies were collected post slaughter from healthy, ID and footrot feet. Samples were fixed, processed and stained with: (1) Haematoxylin and eosin for assessment of cellular and intercellular morphology, (2) Periodic acid-Schiff for basement membrane assessment, (3) Masson’s trichrome for the evaluation of tissue collagen and (4) Tissue Gram stain for the detection of bacteria with the observer blinded to the clinical condition.
The histopathology scoring approach includes (1) semi-quantitative grading of inflammatory cell infiltration into epidermis and dermis, collagenous tissue deposition and bacterial clusters, (2) measurements of epidermal thickness and (3) presence or absence of features such as abscesses, oedema, congestion, haemorrhage, karyopyknosis, cell ballooning and detachment of stratum corneum of the epidermis.
Initial investigations have shown high levels of inflammation in footrot samples with occasional abscesses, cellular degeneration (ballooning and karyopyknosis) and bacterial clusters in epidermis and dermis. Comprehensive histopathological findings from this study will enhance our understanding of footrot pathogenesis while the scoring system will standardise our interpretation of footrot lesions.