A reduced potential for lameness bacterial transmission by Lucilia sericata larvae and flies through metamorphosis.

Lameness in sheep is one of the most serious issues on farms in the UK and worldwide, affecting over 90% of all UK sheep flocks. Despite its severity and prevalence, there are knowledge gaps regarding transmission routes of bacterial pathogens associated with infectious lameness in sheep. As larvae of Lucilia sericata are commonly found on foot lesions on lame sheep, it was hypothesised that the flies or their larvae could harbour lameness associated bacteria. This study examined the gut contents of larvae obtained from the foot lesions of lame sheep and compared them to control larvae collected from infested cat food on the same farm. Of particular interest, were the presence of three different bacterial genera associated with lameness; Fusobacterium necrophorum, Dichelobacter nodosus and Treponema spp., for which viability was also investigated. Larvae were cultured In vitro and some allowed to metamorphose into flies before specific PCR assays were carried out on the gut contents. Results showed a significant association between the bacteria on the feet of the sheep and those within the larvae. Although the gut contents of all larvae found on sheep feet contained one or more of the lameness bacteria, none of the bacteria were recovered from the adult flies, suggesting a level of gut remodelling during metamorphosis. Interestingly, Treponema spp. and Fusobacterium spp. were viable when isolated from gut contents of larvae. Maintenance of infection from larvae to fly did not occur. However, it still remains important to control both disease and insect populations of farms to maintain animal welfare.

Comparison of clinical cure rates from footrot and contagious ovine digital dermatitis using zinc sulphate foot bathing and topical oxytetracycline: A randomised trial.

BACKGROUND: This study reports the clinical cure rates of topical oxytetracycline and 10% zinc sulphate foot bathing for treatment of interdigital dermatitis (ID), footrot (FR) and contagious ovine digital dermatitis (CODD) in lambs. METHODS: The study was a randomised controlled trial of 75 lambs. Group A (n = 38) was foot bathed daily for 5 days in 10% zinc sulphate for 15 minutes and group B was treated with daily topical oxytetracycline for 5 days. On days 0, 7, 14, 28 and 42, lambs were scored for locomotion and foot lesions were recorded. RESULTS: The initial cure rates for ID were 96.20% and 97.00%; for FR, 100% and 95%; and for CODD, 90.09% and 83.33% for zinc sulphate and oxytetracycline, respectively. By day 42, these had changed to 53.16% and 61% for ID; 47.82% and 70% for FR; and 100% and 83.33% for CODD. There were no significant differences in cure rates between the treatments for most time points. LIMITATIONS: The sample size was small, and further studies in larger cohorts and different classes of sheep are required before the findings can be translated into recommendations for clinical practice. CONCLUSION: Both treatments achieved cure rates that are comparable to reported cure rates using systemic antibiotics and could be an effective alternative.

An Observational Study Investigating Potential Risk Factors and Economic Impact for Bovine Ischaemic Teat Necrosis on Dairy Farms in Great Britain.

Bovine ischaemic teat necrosis (ITN) is an emerging disease of unknown aetiology that affects the teats of dairy cattle. It causes economic and animal welfare issues with many animals being culled. No effective treatments or epidemiological data to inform control strategies are currently available. The aim of this observational study was to investigate farmer-reported experiences and identify potential farm-level risk factors. In January 2018, a questionnaire was sent to a random sample of 1,855 Great Britain (GB) dairy farmers. A usable response rate of 12.3% was obtained. Fifty-one per cent [95% confidence interval (CI): 44.4-57.8%] of farmers reported having experienced ITN on their farm between 1985 and 2018. Rising numbers of farms indicated that ITN is an emerging disease with 46.3% of farmers reporting the first case in the 3 years up to 2018. At the animal level, 47.3% (95% CI: 38.7-55.9%) of the cases occurred during the first lactation and 78.9% (95% CI: 75.2-82.6%) within the first 90 days in milk. Only 20.8% (95% CI: 15.9-26.4%) of the cases were reported to recover, whereas 22.8% (95% CI: 17.8-28.5%) of the cases required culling. The remaining cases experienced complications such as loss of a teat and/or mastitis. From these data, the cost of ITN, through production losses and expenditure, was estimated to be £1,121 per farm per year. The costs were estimated at £720, £860 and £2,133 for recovered, complicated and culled cases, respectively. Univariable and multivariable logistic regression models were used to explore the associations between the presence of ITN on farm and various risk factors. The presence of udder cleft dermatitis (UCD) (odds ratio 2.80; 95% CI: 1.54-5.07; p < 0.01) and chapped teats (odds ratio 6.07; 95% CI: 1.96-18.76; p < 0.01) in the milking herd was associated with the presence of ITN at the farm level. This is the first national questionnaire of ITN within GB and highlights the association of UCD and chapped teats with ITN at the farm level. While there are many limitations and potential bias around farmer questionnaires, these findings highlight several key areas for further disease investigation and possible intervention.

Impact of research on contagious ovine digital dermatitis on the knowledge and practices of UK sheep farmers and veterinarians.

BACKGROUND: Contagious ovine digital dermatitis (CODD) is a common foot disease of sheep which causes a severe form of lameness and can be difficult to control. Recent research has provided evidence-based guidance on diagnosis, treatment and farm management control. The aim of this study was to determine the uptake of this guidance on the knowledge and practices of UK sheep farmers and veterinarians and identify priorities for future research. METHODS: Data were collected in 2019-2020 by electronic surveys of UK sheep veterinarians and farmers distributed through sheep industry organisations and social media. RESULTS: Two hundred eight-four sheep farmers and 77 veterinarians responded to the surveys. Fifty-two per cent of farmers and 70% of vets considered that their management of CODD had improved as a direct result of recent research evidence on the disease. The principle areas improved for both sectors were biosecurity advice and use of antibiotic treatments. Farmers and veterinarians reported that the priorities for future research should be in therapeutics, vaccine development and the understanding of disease transmission. CONCLUSION: There has been strong uptake of recent evidence-based veterinary medicine by farmers and veterinarians for the management of CODD, particularly in the areas of biosecurity and responsible antibiotic use.

Contagious Ovine Digital Dermatitis: A Novel Bacterial Etiology and Lesion Pathogenesis.

Contagious ovine digital dermatitis (CODD) is a severe and common infectious foot disease of sheep and a significant animal welfare issue for the sheep industry in the UK and some European countries. The etiology and pathogenesis of the disease are incompletely understood. In this longitudinal, experimental study, CODD was induced in 18 sheep, and for the first time, the clinical lesion development and associated microbiological changes in CODD affected feet are described over time, resulting in a completely new understanding of the etiopathogenesis of CODD. The majority of CODD lesions (83.9%) arose from pre-existing interdigital dermatitis (ID) and/or footrot (FR) lesions. All stages of foot disease were associated with high levels of poly-bacterial colonization with five pathogens, which were detected by quantitative PCR (qPCR): Treponema medium, Treponema phagedenis, Treponema pedis, Dichelobacter nodosus, and Fusobacterium necrophorum. Temporal colonization patterns showed a trend for early colonization by T. phagedenis, followed by F. necrophorum and D. nodosus, T. medium, and then T. pedis, D. nodosus was present at significantly higher predicted mean log10 genome copy numbers in FR lesions compared to both ID and CODD, while Treponema species were significantly higher in CODD and FR lesions compared to ID lesions (p < 0.001). Treatment of CODD-affected sheep with two doses of 10 mg/kg long acting amoxicillin resulted in a 91.7% clinical cure rate by 3 weeks post-treatment; however, a bacteriological cure was not established for all CODD-affected feet. The study found that in an infected flock, healthy feet, healed CODD feet, and treated CODD feet can be colonized by some or all of the five pathogens associated with CODD and therefore could be a source of continued infection in flocks. The study is an experimental study, and the findings require validation in field CODD cases. However, it does provide a new understanding of the etiopathogenesis of CODD and further supportive evidence for the importance of current advice on the control of CODD; namely, ensuring optimum flock control of footrot and prompt isolation and effective treatment of clinical cases.

In vitro susceptibility of contagious ovine digital dermatitis associated Treponema spp. isolates to antimicrobial agents in the UK.

BACKGROUND: Contagious ovine digital dermatitis (CODD) is an important cause of infectious lameness in sheep in the UK and Ireland and has a severe impact on the welfare of affected individuals. The three treponemal phylogroups Treponema medium/Treponema vincentii-like, Treponema phagedenis-like and Treponema pedis spirochaetes have been associated with clinical CODD lesions and are considered to be a necessary cause of disease. There are scant data on the antimicrobial susceptibility of the treponemes cultured from CODD lesions. OBJECTIVE: The aim of this study was to determine in vitro the miniumum inhibitory concentration/ minimum bactericidal concentration (MIC/MBC) of antimicrobials used in the sheep industry for isolates of the three CODD associated treponeme phylogroups T. medium/T. vincentii-like, T. phagedenis-like and T. pedis. ANIMALS: Twenty treponeme isolates; from 19 sheep with clinical CODD lesions. METHODS: A microdilution method was used to determine in vitro the MIC/MBC of 10 antimicrobial agents for 20 treponeme isolates (five T. medium/T. vincentii-like, 10 T. phagedenis-like and five T. pedis). The antimicrobials tested were penicillin G, amoxicillin, oxytetracycline, tilmicosin, lincomycin, spectinomycin, tylosin, tildipirosin, tulathromycin and gamithromycin. RESULTS: The treponeme isolates tested showed low MICs and MBCs to all 10 antimicrobials tested. They were most susceptible to gamithromycin and tildipirosin (MIC90: 0.0469 mg/L), and were least susceptible to lincomycin, spectinomycin and oxytetracycline (MIC90: 48 mg/L, 24 mg/L and 3 mg/L, respectively). CONCLUSIONS: These data are comparable to in vitro antimicrobial susceptibility data for treponemes cultured from bovine digital dermatitis lesions. Dependent on local licensing, penicillin and tilmicosin appear to be the best candidates for future in vivo studies.