Prevalence of Dichelobacter nodosus in western Austrian sheep flocks: Comparison of bacterial cultures, clinical foot rot and lameness with PCR and analysis of sample pooling for PCR diagnosis.

Introduction: Ovine foot rot is a highly contagious and multifactorial claw disease, caused by Dichelobacter nodosus (D. nodosus) and is the main cause of lameness in sheep. The aim of this cross-sectional study was to determine the prevalence of D. nodosus in western Austria both at animal and farm levels. Real-time PCR was evaluated in comparison with clinical and bacteriological investigations from interdigital foot swabs to detect D. nodosus-infected animals. In addition, the use of pooled four-foot swabs to detect foot rot was determined. In course of the study a total of 3156 sheep from 124 farms were examined for lameness and clinical signs of foot rot. The found flock prevalence of D. nodosus was 30,65 % with bacterial culture showing a sensitivity of 75,0 % and a specificity of 100,0 % (p < 0,001) respectively, compared with PCR. Furthermore, clinical foot rot scores (Ckorr = 0,87; p < 0,001) and lameness scores (Ckorr = 0,71; p < 0,001) highly correlated with the detection of D. nodosus by PCR. The result showed that the clinical examination can be used to identify animals infected with D. nodosus in flocks, but PCR must be used to confirm the diagnosis. D. nodosus could be detected equally well with risk-based pools-of-five samples as with undiluted samples (p < 0,001), suggesting that a pool-of-five samples might be a suitable and cost-effective method for detecting D. nodosus in sheep flocks. This study provides an overview of foot rot in Tyrolean sheep flocks and outlines the possibilities and limitations of the various diagnostic tools for D. nodosus. Further studies to investigate possible influencing factors, including alpine pasturing, management factors and biosecurity predisposing to foot rot are necessary for the design of effective future control programs in alpine regions.