Aetiology of ovine footrot in the Portuguese region of Alto Alentejo

The dysbiosis of ovine foot microbiome during the development and treatment of contagious ovine digital dermatitis

BACKGROUND

Contagious Ovine Digital Dermatitis (CODD) is an emerging and common infectious foot disease of sheep which causes severe welfare and economic problems for the sheep industry. The aetiology of the disease is not fully understood and control of the disease is problematic. The aim of this study was to investigate the polybacterial aetiopathogenesis of CODD and the effects of antibiotic treatment, in a longitudinal study of an experimentally induced disease outbreak using a 16S rRNA gene amplicon sequencing approach.

RESULTS

CODD was induced in 15/30 experimental sheep. During the development of CODD three distinct phenotypic lesion stages were observed. These were an initial interdigital dermatitis (ID) lesion, followed by a footrot (FR) lesion, then finally a CODD lesion. Distinct microbiota were observed for each lesion in terms of microbial diversity, clustering and composition. Porphyromonadaceae, Family XI, Veillonellaceae and Fusobacteriaceae were significantly associated with the diseased feet. Veillonellaceae and Fusobacteriaceae were most associated with the earlier stages of ID and footrot rather than CODD. Following antibiotic treatment of the sheep, the foot microbiota showed a strong tendency to return to the composition of the healthy state. The microbiota composition of CODD lesions collected by swab and biopsy methods were different. In particular, the Spirochaetaceae family were more abundant in samples collected by the biopsy method, suggesting that these bacteria are present in deeper tissues of the diseased foot.

CONCLUSION

In this study, CODD presented as part of a spectrum of poly-bacterial foot disease strongly associated with bacterial families Porphyromonadaceae, Family XI (a family in Clostridiales also known as Clostridium cluster XI), Veillonellaceae and Fusobacteriaceae which are predominately Gram-negative anaerobes. Following antibiotic treatment, the microbiome showed a strong tendency to return to the composition of the healthy state. The composition of the healthy foot microbiome does not influence susceptibility to CODD. Based on the data presented here and that CODD appears to be the severest end stage of sheep infectious foot disease lesions, better control of the initial ID and FR lesions would enable better control of CODD and enable better animal welfare.

The microbiome of the footrot lesion in Merino sheep is characterized by a persistent bacterial dysbiosis

Footrot is prevalent in most sheep-producing countries; the disease compromises sheep health and welfare and has a considerable economic impact. The disease is the result of interactions between the essential causative agent, Dichelobacter nodosus, and the bacterial community of the foot, with the pasture environment and host resistance influencing disease expression. The Merino, which is the main wool sheep breed in Australia, is particularly susceptible to footrot. We characterised the bacterial communities on the feet of healthy and footrot-affected Merino sheep across a 10-month period via sequencing and analysis of the V3-V4 regions of the bacterial 16S ribosomal RNA gene. Distinct bacterial communities were associated with the feet of healthy and footrot-affected sheep. Infection with D. nodosus appeared to trigger a shift in the composition of the bacterial community from predominantly Gram-positive, aerobic taxa to predominantly Gram-negative, anaerobic taxa. A total of 15 bacterial genera were preferentially abundant on the feet of footrot-affected sheep, several of which have previously been implicated in footrot and other mixed bacterial diseases of the epidermis of ruminants. Some, including Porphyromonas, can trigger a shift in the composition of bacterial communities and may therefore be of significance to the expression of footrot. A comparison of the communities in footrot lesions of different scores and at different times revealed that this state of dysbiosis is persistent at the active margins of lesions, irrespective of their severity.

Isolation and characterization of Dichelobacter nodosus from ovine and caprine footrot in Kashmir, India

Footrot is a highly contagious and economically important disease of sheep and goats, caused by Dichelobacter nodosus, a slow growing anaerobic Gram-negative rod. The current Australian antigenic classification system, based on variation in the fimbriae, classifies D. nodosus into at least 10 serogroups (A-I and M) and 18 serotypes. This investigation was intended to determine the serological diversity of D. nodosus in this region of Kashmir, India. Exudates of footrot lesions were collected from 24 naturally infected sheep and 42 goats located in the Kashmir valley. Of these 66 samples, 24 yielded evidence of D. nodosus by PCR using 16SrDNA specific primers. Multiplex PCR using serogroup specific primers revealed the presence of serogroup B in all the samples except two, which showed the presence of serogroup E D. nodosus. This study also documents the isolation of D. nodosus and detection of serogroup E for the first time in India.

Current approaches to the management of ovine footrot

Ovine footrot remains the most important cause of lameness in sheep flocks in the UK, despite the existence of proven methods for the control of the disease. Recent research suggests that sheep farmers may be unaware of these methods and may allocate greater resources to treatment of footrot rather than to its prevention. Foot paring, topical treatments, vaccination and parenteral antibiotic therapy all have a role in treating sheep with advanced footrot infections, but prevention of severe infections is best achieved by the timely implementation of control programmes. These are usually based on footbathing and vaccination. For control programmes to be effective it is essential that the pathogenesis and epidemiology of footrot is understood and that control methods are implemented at appropriate times in the season, depending on climatic and pasture conditions. This article reviews these strategies and makes recommendations for steps to reduce the spread of footrot between flocks and to reduce the incidence of footrot within UK flocks.

Minimum inhibitory concentrations for 25 selected antimicrobial agents against Dichelobacter nodosus and Fusobacterium strains isolated from footrot in sheep of Portugal and Spain

The agar dilution method was used to determine the inhibitory activity of 25 antimicrobial agents against 69 strains of Dichelobacter nodosus and 108 strains of the genus Fusobacterium, all of which were isolated from 90 clinical cases of ovine footrot between October 1998 and November 2000. In the case of the micro-organisms belonging to the genus Fusobacterium, the six beta-lactams studied (benzyl penicillin, ampicillin, cloxacillin, cefadroxil, cefuroxime and cephalexine) proved to be, in general, the most effective antimicrobial agents. Chloramphenicol, clindamycin and doxycycline were also quite active against Fusobacterium spp. With regard to the 69 strains of D. nodosus tested, the levels of resistance remain low.

Comparative study of biochemical methods for the identification of Dichelobacter nodosus

The aim of this study was to compare four identification procedures to detect Dichelobacter nodosus and develop a rapid, simple and effective method to identify D. nodosus strains isolated from cases of ovine footrot. The four methods used were: (a) the classic guidelines set down by Holdeman et al. (1977) and Summanen et al. (1993) which are based on gas liquid chromatography (GLC) and different biochemical tests, this method was considered as landmark; (b) Baron and Citron's flowchart for the rapid identification of Gram-negative rod-shaped anaerobes (1997); (c) the API rapid 32 A system (bio Mérieux), and (d) Mast ID Anaerobe ID Ring (MID8) (Mast Diagnostics). None of the four methods used allowed us to correctly identify the D. nodosus strains (neither the strains isolated from cases of ovine footrot nor those originating from type collection). Because of the difficulties encountered in obtaining a correct identification of D. nodosus, we propose a simple, rapid and effective way to achieve this task. Our flowchart will provide the means to identify this microorganism in any laboratory of general microbiology without having to use any specialised equipment.