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Persistence of Dichelobacter nodosus on the feet of sheep: a molecular study

My MRes project works alongside a PhD project funded by the National Environment Research Council (NERC), investigating the survival and persistence of the primary causative agent of ovine footrot, Dichelobacter nodosus.

Ovine footrot (FR) is the most common cause of lameness in sheep in GB. It is a contagious and debilitating disease resulting in pain, poor ewe body condition and weight loss in adults, as well as production losses through reduced growth rates in lambs. Therefore, it is a major negative impact on animal welfare and economics, costing the industry £24 million per annum.

Footrot is identified by an exudative inflammation with a distinct, pungent odour. The two clinical presentations of FR are interdigital dermatitis (ID), characterised by inflammation of the interdigital skin and severe FR (SFR), characterised by necrosis of the epidermal tissues of the hoof with a varying degree of separation of the hoof horn from the underlying tissues. These two clinical presentations are viewed as the same disease, but different states.

The primary causative agent of ovine FR is the gram-negative anaerobic bacterium, Dichelobacter nodosus. Although the presence of D. nodosus is necessary for FR to occur, the disease involves a secondary pathogen, Fusobacterium necrophorum, both working synergistically. Footrot may become re-established in a flock when climatic conditions are favourable for pathogen transmission. This suggests that environmental reservoirs of infection exist.

Evidence shows that D. nodosus may survive longer and at lower temperatures than previously expected. It has been shown that favourable conditions which facilitate the spread of FR has been associated with increased rainfall and temperatures of >10°C. However, evidence suggests that FR can still be transmitted when mean daily temperature is <10°C. It is not quite clear as to why these two results appear contradictory, however as these two studies were performed from different continents with different climates, both could hold true.

My project aims to investigate the persistence of D. nodosus by identifying possible sites of survival (mainly from feet, oral cavity or from faecal matter) and therefore establish whether D. nodosus persists at these sites. Other aims include comparing the presence/bacterial load, disease state and persistence of D. nodosus with the incidence and prevalence of footrot in feet, sheep and flocks. This focuses on capturing the changes that may exist between expected periods of transmission and non-transmission.

Samples collected from individual sheep on farm are processed in order to detect and quantify D. nodosus using PCR-based methods to gather information on bacterial load. These samples are then characterized using an effective molecular typing system to monitor the occurrence and persistence of the pathogen.

The results gathered should increase our understanding of the role of D. nodosus in the epidemiology of ovine footrot and may be useful in the development of management strategies for footrot.



Nicola Liu

N dot L dot B dot H dot Liu at warwick dot ac dot uk


Supervisors:

Professor Laura Green

Laura dot Green at warwick dot ac dot uk

Dr. Kevin Purdy

K dot Purdy at warwick dot ac dot uk