A longitudinal study of the role of Dichelobacter nodosus and Fusobacterium necrophorum load in initiation and severity of footrot in sheep.
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 load(2) 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 load(2) 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.
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK; UCL School of Pharmacy, University College London, 29-39 Brunswick Square, London, UK. Electronic address: l.witcomb@ucl.ac.uk.
Luci A
LA
Witcomb
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK.
Laura E
LE
Green
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK; School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Leicestershire, UK.
Jasmeet
J
Kaler
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK.
Atiya
A
Ul-Hassan
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK.
Leo A
LA
Calvo-Bado
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK.
Graham F
GF
Medley
School of Veterinary Sciences, University of Bristol, Langford House, Langford, UK.
Rose
R
Grogono-Thomas
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, UK.
Elizabeth M H
EM
Wellington
D000818:Animals; D058491:Bacterial Load / Q000662:veterinary; D001426:Bacterial Proteins / Q000032:analysis; D020376:Dichelobacter nodosus / Q000235:genetics / Q000302:isolation & purification; D058066:Digital Dermatitis / Q000453:epidemiology / Q000382:microbiology; D004739:England / Q000453:epidemiology; D005260:Female; D005535:Foot Rot / Q000453:epidemiology / Q000382:microbiology*; D005674:Fusobacterium Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005675:Fusobacterium necrophorum / Q000235:genetics / Q000302:isolation & purification; D016905:Gram-Negative Bacterial Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D006724:Hoof and Claw / Q000382:microbiology*; D008137:Longitudinal Studies; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000662:veterinary; D015995:Prevalence; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000382:microbiology*; D013997:Time Factors
D001426:Bacterial Proteins
Dichelobacter nodosus; Footrot; Fusobacterium necrophorum; Longitudinal study; Quantitative PCR; Sheep