A longitudinal study of the role of Dichelobacter nodosus and Fusobacterium necrophorum load in initiation and severity of footrot in sheep

Abstract

Footrot is an infectious bacterial disease of sheep that causes lameness. The causal agent is Dichelobacter nodosus. There is debate regarding the role of Fusobacterium necrophorum in disease initiation. This research used an observational longitudinal study of footrot, together with quantitative PCR (qPCR) of bacterial load of D. nodosus and F. necrophorum, to elucidate the roles of each species in the development of disease. All feet of 18 a priori selected sheep were monitored for five weeks assessing disease severity (healthy, interdigital dermatitis (ID) and severe footrot (SFR)) and bacterial load. A multinomial model was used to analyse these data.Key unadjusted results were that D. nodosus was detected more frequently on feet with ID, whereas F. necrophorum was detected more frequently on feet with SFR. In the multinomial model, ID was associated with increasing log10 load of D. nodosus the week of observation (OR = 1.28 (95% CI = 1.08–1.53)) and the week prior to development of ID (OR = 1.20 (95% CI = 1.01–1.42). There was no association between log10 load2 of F. necrophorum and presence of ID (OR = 0.99 (95% CI = 0.96–1.02))). SFR was associated with increasing log10 load of D. nodosus the week before disease onset (OR = 1.42 (95% CI = 1.02–1.96)) but not once SFR had occurred. SFR was positively associated with log10 load2 of F. necrophorum once disease was present (OR = 1.06 (95% CI = 1.01–1.11)). In summary, there was an increased risk of increasing D. nodosus load the week prior to development of ID and SFR and during an episode of ID. In contrast, F. necrophorum load was not associated with ID before or during an episode, and was only associated with SFR once present. These results contribute to our understanding of the epidemiology of footrot and highlight that D. nodosus load plays the primary role in disease initiation and progression, with F. necrophorum load playing a secondary role. Further studies in more flocks and climates would be useful to confirm these findings. This study identifies that D. nodosus load is highest during ID. This supports previous epidemiological findings, which demonstrate that controlling ID is the most effective management strategy to prevent new cases of ID and SFR.

The cutaneous ecosystem: the roles of the skin microbiome in health and its association with inflammatory skin conditions in humans and animals

“…In DD lesions, Firmicutes predominated in superficial and intermediate lesions, whereas Treponema dominated the deeper layers of the DD lesions. 56 Another study based on 16S rRNA gene and fluorescent in situ hybridization (FISH), showed approximately that 50% of the sequences were Treponema-like, 25% were of 59,94 Chytrid infection High Composition is driven by chytrid infections 60,61,95 Fusobacterium necrophorum and the remaining were composed of other bacterial species. 93 In a metagenomic study, using shotgun sequencing, it was reported that cattle with DD had increased relative abundances of Spirochaetes, Bacteroidetes and Proteobacteria, in contrast to healthy feet which were colonized predominantly by Firmicutes and Actinobacteria.…”

“…The causative agents for this disease are Dichelobacter nodosus and Fusobacterium necrophorum. 94 Several bacterial taxa have been associated with this disease and, based on a 16S rRNA gene study, 59 microbial diversity and richness was greater in tissues from sheep with interdigital dermatitis, the first clinical sign in footrot lesions, than in healthy interdigital areas, or those with a chronic form of footrot (Table 3). This chronic form is known as virulent footrot and results in separation of the hoof horn from sensitive tissue.…”

A distinct bacterial dysbiosis associated skin inflammation in ovine footrot

“…Fusobacterium necrophorum, also a Gram negative bacterium, is attributed to play a role in the initiation of ID prior to D. nodosus infection1, and/or in the exacerbation of footrot lesions once it is established5. Other bacteria such as Treponema have also been detected in footrot cases, but its role in the disease process remains unclear678.…”

The detection of Dichelobacter nodosus and Fusobacterium necrophorum from ovine footrot in Kashmir, India

“…It was also observed that in 52 samples in which both the anaerobes were detected, the affected sheep had severe footrot with lesion scores mostly 4 in comparison to other footrot affected sheep in which F. necrophorum was absent or found alone. However [9], reported that F. necrophorum load was higher in feet of sheep with severe footrot. The reason for this could be that F. necrophorum plays vital role in creating anaerobic micro environment necessary for establishment of D. nodosus in the infected claws of sheep.…”