Footrot (FR) is a highly infectious and debilitating disease of sheep, which has a significant economic impact on the sheep farming industry, in the UK and worldwide and causes significant suffering of sheep. Despite some recent advances, FR remains a scientifically challenging disease to understand. To help improve our understanding of disease pathogenesis, two culture-independent techniques were developed to examine the microbial succession events between the causative agent, Dichelobacter nodosus and an accessory agent, Fusobacterium necrophorum, the latter also postulated to be involved in disease initiation. The two populations were monitored in relation to disease initiation and progression during a longitudinal study and disease presentation in tissue biopsies (in situ). Finally, the distribution of these two species of bacteria in the environment was examined to highlight possible sources of infection. The work in this thesis has demonstrated that FR is a disease where expression is related to D. nodosus load present in the ovine interdigital space. D. nodosus (rpoD) load increased from that on a healthy foot to one presenting with interdigital dermatitis (ID) and feet with a higher D. nodosus (rpoD) load were more likely to go on to develop FR one week later. FISH analysis of the D. nodosus population present within the epidermis also revealed similar findings; D. nodosus cell counts increased during stages of ID, but the organism was less frequently detected in biopsies from feet with FR. Suggesting that ID might be the most infectious stage of the disease process. A fact that needs to be highlighted to farmers to encourage treatment at this stage of disease. In contrast, F. necrophorum (rpoB) load did not correlate with ID presentation or prior to the development of FR, but increased the week of FR onset. FISH analysis also revealed that F. necrophorum cell counts were higher in feet with FR than those with ID. It is possible therefore that F. necrophorum may thrive in the altered environment of a foot presenting with FR, possibly contributing to disease persistence and severity. Finally, both pathogens were detected in a range of environmental samples from a farm with endemic FR, highlighting possible sources of infection and material, which once contaminated with D. nodosus and F. necrophorum may contribute to the spread of FR. This study has provided an improved understanding of the microbial population dynamics involved in the development of ID and FR in sheep, which may have implications for control and treatment practices not only in the UK, but world-wide.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:560407 |
| Date | January 2012 |
| Creators | Witcomb, Luci |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/50463/ |
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