Om Dhungyel

Dichelobacter nodosus (D. nodosus) is the pathogen responsible for causing footrot in sheep and goats, which poses significant challenges to animal health and welfare. D. nodosus is classified into 10 different serogroups (A–I and M) based on the genetic variation of this fimbrial ( fimA ) gene. These fimbriae are immunogenic and play an important role in virulence, making serotyping of these fimbriae valuable for identification and vaccine development. In this study, three multiplex quantitative polymerase chain reaction (qPCR) assays, targeting the most commonly prevalent nine serogroups (ABC, DEF, and GHI), were studied for the detection of serogroups in foot swab samples collected from Dutch sheep farms. A total of 147 samples tested positive for D. nodosus using pnpA qPCR, and 144 (98%) samples exhibited a serogroup using qPCR. The multiplex qPCRs detected significantly more serogroups than conventional serogroup PCRs and detected more than one serogroup in a swab. In 46 samples (31%, 46/147), two to five different serogroups were identified from a single swab sample. In three samples, no serogroup was identified, likely due to sequence variation in the fimA gene in these samples. These direct multiplex qPCR tests provide faster, more sensitive, and accurate testing for the direct classification and quantification of D. nodosus serogroups for studying the epidemiology of footrot and for the formulation of serogroup-specific targeted vaccination strategies for prevention, control, and treatment of footrot.

The study objectives were to understand the practices and perceptions of sheep farmers and district veterinarians (DVs) towards sheep health management and, the impact of disease at the farm level in addition to the availability, accessibility, and use of veterinary services. Data were collected using question-based surveys, distributed online and in-person to sheep farmers (45 respondents) and DVs (25 respondents). Most farmers were male, ≥51 years old, who placed a high priority on the health and welfare of their sheep. For disease prevention most farmers vaccinated their sheep (91%) and 86.7% had a farm biosecurity plan, although its components and their application varied, e.g., the isolation of new or sick sheep. Fencing costs were most frequently identified (70.5% respondents) as a financial concern for sheep farmers. Their most common sources of information about disease control and prevention were DVs (66.7%), private veterinarians (60.0%), the internet (42.9%), rural suppliers (35.7%), and farmers/neighbours (28.6%). Fifty-eight percent of farmers reported a long distance from veterinarian services. Farmers preferred to receive information via email (77.8%), whereas 56% of DVs preferred to share information via phone call. This discrepancy presents an opportunity to align these mechanisms more closely for effective dissemination of information and increased producer engagement.

The aims of this study were to develop an understanding of farmers' perceptions and risk factors for footrot, including its less severe forms, and other hoof diseases in sheep in New South Wales (NSW). A questionnaire was developed and administered to sheep farmers in Local Land Services (LLS) regions across NSW. LLS staff selected sheep farmers who met the inclusion criteria which included farmers with a minimum of 100 sheep, a history of having had foot problems in their flock or having expressed an interest in improving sheep health and production. Farmers completed the questionnaire either by telephone or via the REDCap online survey platform. Descriptive analyses and multivariable logistic regression models were created. The survey was completed by 43 sheep farmers with a median farm size of 1,500 Ha and flock size of 2,300; footrot was present on 39% of farms while 75.6% had other hoof diseases. A flock of >3,000 sheep were more likely to have footrot than a smaller flock (OR = 11.99, 90% CI = 3.02–63.92, P-value = 0.005) and footrot was less likely to be present on farms when an Animal Health Statement was requested while purchasing sheep (OR = 0.10, 90% CI = 0.01–0.56, P-value = 0.04). Hoof conditions other than footrot were likely to be present in flocks when foot inspections were conducted at a time other than weekly inspections (OR = 0.13, 90% CI = 0.01–0.68, P-value = 0.04) and flocks kept on undulating ground were more likely to have diseases other than footrot compared to those kept on flat ground (OR = 3.72, 90% CI = 1.02–15.80, P-value = 0.09). Most farmers agreed that footrot including its less severe forms can cause production losses and negatively affect animal health and welfare. Limitations of the study were the sample size and dry environmental conditions prior to and during study period in many regions of NSW which limited the expression of footrot.

Objective: The aim of this study was to determine the efficacy of serogroup‐specific bivalent fimbrial vaccines in the control and elimination of relatively mild (intermediate) forms of footrot in sheep flocks in NSW, there being some evidence that such forms are difficult to control.Methods: Four flocks of sheep with history of footrot of intermediate virulence were selected based on clinical and bacteriological diagnoses. Dichelobacter nodosus serogroups included in bivalent vaccines at each farm were based on on‐farm serogroup‐prevalence data. Two doses of bivalent vaccine were administered with a 4‐week interval between doses. Repeated post‐vaccination inspections of all feet of between 100 and 119 animals per mob were conducted and foot swabs were collected for bacteriological testing. Blood samples were collected from 10 to 24 individually identified animals per flock at each inspection to check for agglutinating antibody responses.Results: In the majority of animals, antibody levels for serogroups included in each vaccine were above the level believed to be required for protective immunity. Footrot disappeared on farm 1 prior to vaccination, but did not reappear postvaccination. Footrot was controlled but not eliminated on farms 2, 3, and 4, where the prevalence and severity of the disease and number of serogroups present were reduced.Conclusion: Serogroup‐specific bivalent vaccines can be effective at controlling footrot caused by intermediate strains of D. nodosus.

Objectives: The primary objective of this study was to evaluate the clinical virulence of aprV2‐positive lesser virulent field isolates of footrot bacteria Dichelobacter nodosus in comparison with an aprV2‐positive clinically virulent reference strain. Correlations between the clinical expression of the disease and the presence of aprV2 (detected using PCR tests) have been inconsistent. A second objective was to evaluate the elimination of D. nodosus following treatment of sheep as some strains of D. nodosus have been reported to be difficult to eliminate.Methods: The virulence of three aprV2‐positive field isolates of D. nodosus which had lesser virulent phenotypes, and an aprV2‐positive virulent reference strain was evaluated in a sheep trial using a pasture‐based experimental infection model. In the second phase of the study, treatments including footbathing and a long‐acting antibiotic were administered and their efficacy in elimination of these strains was evaluated.Results: Severe underrun (score 4) lesions developed in sheep infected with the aprV2‐positive virulent reference strain but not in sheep infected with the field isolates; they had mild lesions (score 2 or 3). The three field isolates and the virulent reference strain of D. nodosus were eliminated by intensive foot bathing and antibiotic therapy in combination with housing the animals in dry conditions post‐treatment.Conclusion: The results suggest that the presence of aprV2 gene in isolates of D. nodosus may not be a reliable indicator of virulence and that further investigation of the factors that determine clinical virulence is required. While the treatment regime was successful, based on a range of considerations, the use of such an intensive treatment involving antibiotics should be limited to small groups of high‐value animals, such as rams.