Investigating the Polymicrobial Nature of Bovine Digital Dermatitis in Natural Infections and Animal Models
Date
2024-12-12
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Abstract
Digital Dermatitis (DD) is a multifactorial, polymicrobial skin disease on cattleās feet and is the leading cause of lameness in Canadian dairy cattle, with an etiology that remains unclear. This thesis aimed to investigate the polymicrobial nature of DD by identifying potential bacterial reservoirs and investigating the roles of specific bacteria in lesion initiation in natural infections. Additionally, efforts were made to optimize a bovine infection model. Four studies were conducted, three field studies in commercial dairy farms and an experimental infection study. We relied on quantitative molecular techniques, real-time qPCR, targeting three DD-associated Treponema spp. and four other anaerobes. First, we validated swabs as an alternative to invasive skin biopsies in detecting and quantifying DD bacteria. We then mapped and quantified DD bacteria in potential reservoirs in dairy cows from herds with or without DD. Next, we assessed the temporal changes in bacterial counts preceding lesions and determined whether bacterial presence in reservoirs was persistent or transient in a longitudinal study. Finally, we explored a novel tattoo-based inoculation method to optimize DD bovine models. DD-Treponema spp. were detected only in DD-affected herds, while non-treponemal anaerobes were widespread in both affected and DD-negative herds. Although all target bacterial species were occasionally detected on healthy skin and in saliva, only Porphyromonas levii and Fusobacterium necrophorum seem to persist in these sites. Despite their detection in environmental samples, we did not detect any of the target species in feces. All target species increased in numbers before lesion onset, with sequential colonization starting with non-treponemes two weeks before DD occurred, followed by DD-Treponema spp. Lastly, the tattooing method showed potential for future use in experimental induction of DD by depositing Treponema spp. at the epidermis-dermis junction; however, we were unable to induce lesions in dairy calves likely due to factors missing in our model. While DD etiology remains undetermined, this thesis supports the key role of Treponema spp. in the disease, offers a change in perspective on the involvement of non-treponemes in lesion initiation, discusses the challenges in reproducing this disease experimentally, and proposes a hypothetical scheme of pathogenesis for this complex disease.
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Keywords
Dairy cattle, Hoof infectious disease, Lameness, Treponema, Porphyromonas, Fusobacterium, Real-time qPCR
Citation
Petersen Dias, A. (2024). Investigating the polymicrobial nature of bovine digital dermatitis in natural infections and animal models (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.