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.