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Title: Identifying infection reservoirs of digital dermatitis in dairy cattle
Author: Bell, J.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Digital dermatitis (DD) is an infectious ulcerative dermatitis typically affecting the skin of the hind feet of dairy cattle worldwide with substantial welfare and economic implications making it an important issue for the dairy industry. A polytreponemal aetiology has been described with three distinct cultivable treponeme phylogroups (Treponema medium, Treponema phagedenis and Treponema pedis) consistently detected within DD lesions in the UK and USA. Current control strategies are failing to eliminate DD on farm and there is little known about DD transmission. Identifying the infection reservoirs of DD treponemes would inform new targeted prevention strategies for DD. Dairy cattle gingiva, recto-anal junction (RAJ) and DD-unaffected foot tissue (previously identified as potential infection reservoirs) along with samples from the dairy farm environment were surveyed for the presence of DD treponemes by molecular and cultivation techniques to determine their role as infection reservoirs. DD treponemes were detected in 14/122 gingiva sampled, 2/121 RAJ sampled and 41/217 DD-unaffected feet. No temporal association with presence of DD treponemes in these tissue types was identified. Detection of DD treponemes in dairy cattle faeces (n=62), mucin casts (n=31), water (n= 19) and feed samples (n=36) failed by PCR, despite use of optimised detection techniques for DD treponemes in faecal material. However, for the first time a treponeme belonging to the T. phagedenis DD treponeme phylogroup was isolated from a dairy cattle faecal culture. In addition, a second faecal culture was also positive by PCR for the T. phagedenis DD treponeme phylogroup. DD treponemes were detected on dairy cattle fomites with 9/16 foot trimmer gloves positive for DD treponemes which were only detected following DD-affected foot handling. DD treponemes were also detected on a small number of foot trimming tools other than the foot trimming knife blades. Additionally, for the first time, DD treponemes were detected in 22/169 dairy cattle footprints, with the largest proportions detected in footprints on concrete and rubber floors. Further investigation into the carriage of DD treponemes in tissues using histopathology and immunohistochemistry (IHC) on tissues demonstrated that gingiva and RAJ tissue had no signs of disease; however, almost all healthy foot tissue (PCR positive for DD treponemes) appeared to have changes in the tissue associated with infection. Multi-locus sequence typing (MLST) revealed that the same sequence types of the DD treponeme phylogroups found in DD lesions of various species could also be found in gingiva, RAJ and DD-unaffected foot tissue of dairy cattle. Survival of DD treponemes was assessed in a range of different conditions, with DD treponemes remaining viable when cultured between the pH values of 5.5 and 9 and in temperatures of 4-37 °C under anaerobic conditions. DD treponemes remained viable in faecal microcosms incubated aerobically for a median of 1 day (range of 0-6 days). In five different bedding microcosms under aerobic conditions, DD treponemes were viable for the full 7 days of the study in sand bedding, for 6 days in sawdust and for 5 days in recycled manure solids (RMS). However, DD treponemes were not viable at any time point when inoculated into bedding microcosms of straw or sand containing 5% (w/w) lime. In conclusion, these studies have demonstrated that DD treponemes have a diverse range of potential infection reservoir sites including the gastrointestinal (GI) tract and fomites, and along with survival information, this knowledge can be applied to the development of preventative measures to mitigate DD transmission.
Supervisor: Evans, Nicholas ; Carter, Stuart ; Murray, Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral