Treponema spp. associated with digital dermatitis in Norwegian cattle and development of a diagnostic qPCR

Bovine digital dermatitis (DD) is a painful infectious disease of cattle limbs, causing lameness and major economic and welfare issues. Its prevalence is increasing in Norway, yet diagnosis relies on clinical signs due to the lack of validated laboratory tests. This study applied 16S rDNA sequencing to identify Treponema species associated with DD and aimed to develop a specific PCR assay. A secondary goal was to assess swab samples as a non-invasive alternative to biopsies. Samples (n = 225) from 187 cows in 38 herds (31 DD-affected, 7 DD-free) were collected in 2018 and 2023 from DD lesions, mild dermatitis, and healthy feet. Treponema phylotypes PT1, PT6, PT12, and PT19 dominated DD lesions; PT19 also appeared in DD-free herds. Two PCR assays targeting PT1 and PT6 were successfully developed. Swab and biopsy samples from 23 matched lesions showed strong correlation, supporting swabs as a viable alternative. This is the first deep sequencing study of DD lesions in Norwegian cattle. It enabled PCR assay development for DD-associated Treponema and demonstrated that swabs provide a less invasive diagnostic sampling option.

牛指（趾）间皮炎（Bovine digital dermatitis，简称DD）是一种引发奶牛肢部疼痛的传染性疾病，可导致跛行并造成严重的经济损失与福利问题。该病在挪威的发病率呈上升趋势，但由于缺乏经过验证的实验室检测手段，目前DD的诊断仍依赖临床症状。本研究采用16S rDNA测序技术鉴定与DD相关的密螺旋体属（Treponema）菌种，旨在开发特异性聚合酶链式反应（Polymerase Chain Reaction，PCR）检测方法，次要目标为评估拭子样本作为活检术非侵入性替代采样手段的可行性。研究于2018年至2023年间，从38个牛群（其中31个为DD感染牛群，7个为未感染牛群）的187头奶牛身上采集了225份样本，采样部位涵盖DD病灶、轻度皮炎患处及健康足部。密螺旋体系统型PT1、PT6、PT12与PT19为DD病灶中的优势菌群，其中PT19同时在未感染DD的牛群中被检出。本研究成功开发出针对PT1与PT6的两种PCR检测方法；对23处匹配病灶的拭子样本与活检样本进行比对分析后发现，二者具有极强的相关性，证实拭子采样是切实可行的替代方案。本研究为挪威首次针对奶牛DD病灶的深度测序研究，不仅成功开发出针对DD相关密螺旋体的PCR检测方法，同时证实拭子采样是一种侵入性更低的诊断采样手段。