Do Treponemes in Bovine Digital Dermatitis-Associated Claw Horn Lesions Preclude Co-Infection by Pyogenic Bacteria?

Bovine digital dermatitis (BDD) is an infectious claw disease chiefly induced by treponemes, while deep digital sepsis (DDS) is caused by pyogenic bacteria. It is currently unclear why persistent BDD-associated claw horn lesions (BDD-CHL) do not develop DDS. One possible explanation could be that the intralesional presence of treponemes makes it more difficult for pyogenic bacteria to colonize BDD-CHL. To lay the groundwork for exploring this possibility, we determined the presence and amounts of treponemes and selected pyogenic bacteria in BDD-CHL versus DDS at the DNA level. "Total Treponema" (TT-)PCR and type-specific qPCR were used to screen 18 BDD-CHLs from 15 cows and 18 DDS samples from 11 cows for bacterial DNA. TT-PCR identified Treponema DNA as most abundant DNA in 8/18 BDD-CHLs and 1/18 DDS samples. qPCR revealed Treponema pedis DNA in all BDD-CHLs, and one DDS lesion. Fusobacterium necrophorum DNA was significantly more abundant in DDS compared to BDD-CHL samples (p = 0.027). Both lesion types harbored similar mean levels of Trueperella pyogenes DNA. Interestingly, 7/18 DDS samples contained Parvimonas DNA. Our DNA-based data call for downstream studies involving living BDD-CHL-associated Treponema species and F. necrophorum, and, importantly, point to a possible pathogenic role of Parvimonas in DDS.