New South Wales Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, New South Wales, 2568, Australia.
Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, New South Wales, 2570, Australia.
Aust Vet J. 2023 Dec;101(12):522-530. doi: 10.1111/avj.13295. Epub 2023 Oct 4.
Ovine footrot is a contagious bacterial disease that causes foot lesions, and depending on the virulence of the causative strains, may lead to severe underrunning of the hoof and lameness. Virulent footrot can be identified, treated and controlled more effectively than less virulent benign forms. The in vitro elastase test for virulence of the causative bacteria, Dichelobacter nodosus, has been used to support clinical diagnosis. However, not all laboratory-designated virulent D. nodosus strains cause clinical signs of virulent footrot. This study evaluated retrospectively how well the elastase test supported clinical footrot diagnosis in 150 sheep flocks examined for suspect footrot in New South Wales between August 2020 and December 2021. Flocks were included if measures of clinical disease, environmental conditions and the virulence of D. nodosus isolates were available. Variation in the elastase activity result between D. nodosus isolated from the same flock made bacterial virulence hard to interpret, but calculating the mean elastase rate for all isolates from the same flock made correlations between bacterial virulence and flock footrot diagnosis possible. Simplifying bacterial virulence into whether there were any elastase-positive D. nodosus isolates before 12 days increased the predictive value of elastase results for virulent diagnosis, compared with using the first day that any isolate was elastase positive or the percentage of elastase-positive isolates by 12 days, but not all clinically virulent flocks had isolates with elastase activity before 12 days. Logistic regression models were fitted to identify the minimum number of predictors for virulent footrot diagnosis, with models suggesting that virulent footrot diagnosis was best predicted by adding the elastase test result and environmental conditions to the prevalence of severe foot lesions (score 4 and 5). However, performing the same analysis with different breeds, ages of sheep and seasons might highlight other factors important in the diagnosis of virulent footrot.
绵羊腐蹄病是一种传染性细菌性疾病，会导致蹄部病变，并且根据致病菌株的毒力，可能导致蹄壳严重腐烂和跛行。毒力较强的腐蹄病可以比毒力较弱的良性形式更有效地识别、治疗和控制。体外弹性蛋白酶试验用于检测致病细菌双形诺维氏梭菌的毒力，已用于支持临床诊断。然而，并非所有实验室指定的毒力双形诺维氏梭菌菌株都会引起毒力腐蹄病的临床症状。本研究回顾性评估了在 2020 年 8 月至 2021 年 12 月期间对新南威尔士州疑似腐蹄病的 150 个羊群进行检查时，弹性蛋白酶试验对临床腐蹄病诊断的支持程度。如果有临床疾病、环境条件和双形诺维氏梭菌分离株的毒力的测量值，则包含羊群。同一羊群分离的双形诺维氏梭菌之间的弹性蛋白酶活性结果的差异使得细菌毒力难以解释，但计算同一羊群所有分离株的平均弹性蛋白酶率使得细菌毒力与羊群腐蹄病诊断之间的相关性成为可能。将细菌毒力简化为在 12 天之前是否有任何弹性蛋白酶阳性的双形诺维氏梭菌分离株，与使用任何分离株首次出现弹性蛋白酶阳性或 12 天内弹性蛋白酶阳性分离株的百分比相比，增加了弹性蛋白酶结果对毒力诊断的预测值，但并非所有临床毒力的羊群在 12 天之前都有具有弹性蛋白酶活性的分离株。拟合逻辑回归模型以确定用于毒力腐蹄病诊断的最小预测因子数量，模型表明，通过将弹性蛋白酶试验结果和环境条件添加到严重蹄部病变的患病率（评分 4 和 5）中，可更好地预测毒力腐蹄病的诊断。然而，使用不同品种、绵羊年龄和季节进行相同的分析可能会突出诊断毒力腐蹄病的其他重要因素。
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