The efficacy of
salicylic acid paste (SA) in the treatment of ulcerative
bovine digital dermatitis (
BDD) was assessed by combining clinical and histopathological analyses with molecular
biological techniques. The latter were conducted in a blinded manner to reach maximum objectivity. Prior to treatment, M2-stage
BDD lesions (n = 26, diagnosed in 21 dairy cows) exhibited ulceration, with severe perivascular, chronic, lymphoplasmacytic
dermatitis and extensive keratinolysis being noted in most cases. Pretreatment biopsy samples (n = 12) followed by
povidone-iodine ointment under
bandage for one week before administration of SA
paste were tested positive for Treponema spp. by blinded PCR and fluorescent in situ hybridization (FISH). Subsequent treatment consisted of application of SA and bandaging at weekly intervals until lesions had completely resolved. The
treatment duration ranged between 2 and 4 weeks. Complete healing was achieved in 100% of cases, with 2/21 animals requiring a second round of treatment upon disease reoccurrence. Importantly, only 3/26 biopsies taken from previously affected sites still tested positive by Treponema PCR, and in another biopsy, the outermost layers of the stratum corneum scored weakly positive by Treponema-specific FISH. None of these Treponema
DNA-positive biopsies showed signs of ulceration. One case exhibited focal keratinolysis. Positive PCR or FISH in these cases may have arisen from
DNA traces of dead bacteria or environmental contamination during biopsy harvesting. To our knowledge, this is the first study on blinded molecular biological monitoring of the therapeutic efficacy of SA with respect to
treponemal infection, and on complete
BDD M2-stage remission in all animals achieved by SA treatment according to an optimized protocol. Although the etiology of
BDD is considered as multifactorial, our data further support the concept that treponemes have a decisive role in
BDD pathogenesis.