Comparison of footbathing treatments for ovine footrot using formalin or zinc sulphate

A field trial was carried out to compare 3 topical treatments for ovine footrot. They were preliminary hoof paring with weekly footbathing either in 10% formalin, or in 10% zinc sulphate + 0.2% anionic surfactant ('Teepol'), or twice-weekly footbathing in the same zinc sulphate-surfactant mixture without hoof paring. Control sheep were not treated. Within 21 days, the number and severity of active lesions of footscald and footrot among treated sheep were substantially reduced by comparison with the controls; no significant differences were observed between treatments. Treatment effects were also comparable against mild footrot infection of the sole or heel region, hut in the more advanced lesions the healing response to paring and zinc footbathing was superior to that from paring and formalin footbathing (P<0.01). Twice-weekly footbathing in zinc-surfactant solution was effective in preventing new footrot infection. No chronic toxic effects attributable to zinc sulphate at a concentration of 10% were demonstrable in the hoof integument either clinically or histologically.     

Eradication of ovine footrot by repeated daily footbathing in a solution of zinc sulphate with surfactant

OBJECTIVE: To investigate the effect on ovine footrot of repeated daily footbathing in a solution of zinc sulphate with surfactant. DESIGN: Merino sheep were allocated to control and treatment groups of 119 sheep each at week 0. The sheep had a history of S1, U1, T and/or U6 types of Dichelobacter nodosus in interdigital and underrunning footrot lesions. Feet were not pared prior to treatment. PROCEDURE: Treatment sheep were footbathed in a 15 to 18% (w/v) solution of zinc sulphate with surfactant for 10 min on five consecutive days during week 1. At week 2, and fortnightly to week 52, all feet were inspected, lesion scores were recorded and samples were taken for laboratory tests. At week 53, all feet with no lesions at week 52, but with underrunning lesions prior to week 1, were pared and samples were taken. RESULTS: After footbathing, there were no lesions in any treatment sheep at any inspection to week 52. The percentage of feet of control sheep with lesions increased from 9% (391 of 4,284) between weeks 20 and 36, to 14% (593 of 4,284) between weeks 36 and 52. Ninety-five of 96 control sheep with no lesions at week 20 were still asymptomatic at week 52. D nodosus was not isolated from samples taken from 99 and 87 pared feet of treatment and control sheep, respectively. CONCLUSION: Repeated daily footbathing combined with prolonged exposure to a dry environment eradicated footrot in sheep with both interdigital and underrunning lesions in feet that were not pared prior to treatment.     

Failure to eradicate ovine footrot associated with Dichelobacter nodosus strain A198 by repeated daily footbathing in zinc sulphate with surfactant

OBJECTIVE: To investigate the effect of repeated daily footbathing in zinc sulphate on virulent ovine footrot associated with S1, U1 and U5 zymogram types of Dichelobacter nodosus, including the highly virulent S1 strain A198. DESIGN: A field trial with experimentally infected sheep. PROCEDURE: At week 0, 50 sheep were infected with D. nodosus strains A198 (S1), C305 (U1), BC3993 (U5) and BC3995 (U5). At weeks 1 and 47, respectively, 169 and 235 uninfected sheep were added. At week 60, sheep were allocated to control and treatment groups each containing 220 sheep. Every 2 or 4 weeks to week 113, feet were inspected, and lesions were scored and sampled. Treatment sheep were footbathed in 15 to 18% (w/v) zinc sulphate with surfactant for 5 consecutive days (10 min per day) during week 61. During week 110, the footbathing protocol was applied again, this time to all surviving treatment and control sheep. RESULTS: BC3993 and A198 were isolated from 57% (162 of 285) and 20% (58 of 285), respectively, of new lesions sampled between weeks 3 and 13, and 21% (57 of 271) and 50% (136 of 271) between weeks 49 and 59. Percentages of new lesions associated with C305 and BC3995 remained constant. During the initial 17 weeks after footbathing at week 61, 90% (75 of 83) and 19% (95 of 490) of lesions in treatment and control sheep, respectively, were score 4 or 5, and 94% (47 of 50) and 38% (33 of 87) of those were associated with A198. CONCLUSIONS: Repeated daily footbathing did not eradicate virulent ovine footrot because strain A198 produced deep, covert lesions that facilitated the survival of D. nodosus.     

Improved diagnosis of virulent ovine footrot using the intA gene

Footrot is a mixed bacterial infection of the hooves of sheep. The gram-negative anaerobic bacterium Dichelobacter nodosus is the principal causative agent, with different strains causing diseases of different severity, ranging from benign to virulent. In Australia, in the state of New South Wales (NSW), only virulent footrot is subject to regulatory action, including quarantine. However, it is often difficult to distinguish benign footrot from virulent footrot in the initial stages of infection, or under adverse climatic conditions. The gelatin gel test, which measures the thermostability of secreted bacterial proteases, is the laboratory test most widely used in Australia to aid in the differential diagnosis of footrot. The proteases of virulent strains are, in general, more thermostable than the proteases of benign strains. However, there are some false positives in the gelatin gel test, which may lead to unnecessary quarantine procedures. We used Southern blot analysis on 595 isolates of D. nodosus from 124 farms on which sheep had benign or virulent footrot to test for the presence of the intA gene. We found that for D. nodosus strains which are stable in the gelatin gel test, there is a high correlation between the presence of the intA gene and the ability of the strain to cause virulent footrot. We also developed a PCR-based assay for the rapid detection of intA, which can be used to test DNA extracted from colonies grown on plates, or DNA extracted from cotton swabs of culture plates.     

Factors associated with the effectiveness of antibiotic treatment for ovine virulent footrot

Factors associated with the proportion of sheep cured of virulent footrot after antibiotic treatment were studied in a field trial under dry environmental conditions. From 2 similar flocks, 1091 Merino sheep weighing about 50 kg and infected with virulent footrot received an intramuscular injection of either 12 mL of a mixture of penicillin (250 mg/mL) and streptomycin (250 mg/mL), 6 mL of long acting oxytetracycline (200 mg/mL) or 6 mL of a mixture of lincomycin (50 mg/mL) and spectinomycin (100 mg/mL). Variables that were significantly associated with the proportion of sheep cured were: the type of antibiotic used, the number of feet infected and the flock from which the sheep came. There was an interaction between antibiotic type and number of feet infected and between antibiotic type and flock in association with the proportion of sheep cured. The extent of paring and the occurrence of blowfly strike in footrot lesions treated with diazinon had no significant association with the proportion of sheep cured.     

Treatment of virulent footrot with lincomycin and spectinomycin

A mixture of lincomycin and spectinomycin was investigated as a treatment for footrot in sheep. In a controlled clinical trial 92.5% of acute and chronic cases of virulent footrot were cured following a single intramuscular injection of a mixture containing 50 mg lincomycin and 100 mg spectinomycin/ml at a dose rate of 1 ml/10 kg bodyweight. No improvement in clinical response was observed in groups of sheep treated on 3 successive days with this dose rate nor in another group treated once at a dose rate 1 ml/3.3 kg bodyweight. Cure effectiveness of each of the 3 treatment groups relative to untreated controls was 89%, 95% and 95%. Efficacy of lincomycin/spectinomycin was compared with that of penicillin/streptomycin in the treatment of footrot on 2 farms in south western New South Wales. Assessments made 14 to 17 d after treatment showed that on one farm all 122 ewes treated with lincomycin/spectinomycin had recovered while 170 of 175 ewes treated with penicillin/streptomycin recovered in the same period. On the second farm 87 of 90 ewes treated with lincomycin/spectinomycin recovered, compared with 184 of 190 sheep in the same flock treated with penicillin/streptomycin. Supportive footbathing did not seem to improve the clinical response in either treatment group and the paring done was sufficient only to establish diagnosis and to remove grossly overgrown horn.     

Comparative antigenic analysis of extracellular proteins of Bacteroides nodosus isolated from virulent and benign ovine footrot

Antigens in the extracellular protein (ECP) complexes of Bacteroides nodosus, isolated from sheep with either benign or virulent footrot, were studied by immunoelectrophoresis (IEP). Rabbit antisera against ECP from virulent and benign strains, were used in homologous and heterologous crossed IEP. Four precipitin peaks unique to the virulent strain, and five peaks unique to the benign strain were identified. In an attempt to characterize the different antigens in ECP, rabbit antisera were raised against an outer membrane protein (OMP, mol. wt. 35 000 daltons), pili and various proteases of virulent and benign strains of B. nodosus. No precipitin band was observed when ECP from both B. nodosus strains were reacted against anti-OMP and anti-pilus antisera. However, single precipitin bands unique to one protease from the benign strain and one protease from the virulent strain were identified. The results suggest that specific antigens other than proteases or pili are important in determining whether a B. nodosus isolate is virulent or benign.     

The pathogenesis of ovine footrot

Ovine footrot is a contagious and debilitating disease that is of major economic significance to the sheep meat and wool industries. The causative bacterium is the gram negative anaerobe Dichelobacter nodosus. Research that has used a classical molecular genetics approach has led to major advances in our understanding of the role of the key virulence factors of D. nodosus in the disease process. D. nodosus strains produce polar type IV fimbriae and extracellular serine proteases. Mutagenesis of the fimbrial subunit gene fimA and the pilT gene, which is required for fimbrial retraction, and subsequent testing of these mutants in sheep virulence trials has shown that type IV fimbriae-mediated twitching motility is essential for virulence. The extracellular protease genes aprV2, aprV5 and bprV have also been mutated. Analysis of these mutants has shown that ArpV5 is the major extracellular protease and that AprV2 is the thermostable protease that is responsible for the extracellular elastase activity. Structural analysis of AprV2 has revealed that it contains several novel loops, one of which appears to act as an exosite that may modulate substrate accessibility. Finally, virulence experiments in sheep have shown that the AprV2 protease is required for virulence.     

Onset and remission of ovine footrot

SUMMARY Sheep exposed to uncontrolled outbreaks of footrot were observed on one farm for 3 successive years and on another for one year. Observations were made from mid-winter to early summer. In each outbreak about 70% or more of sheep exposed to footrot acquired the disease. Natural remission occurred in each outbreak and some cases healed while new cases continued to develop. A feature of all outbreaks observed was that a much higher proportion of late onset cases healed than cases which developed early in the outbreaks. By contrast, 90% of sheep already affected before spring had lesions which persisted into next summer. It is suggested that there is a spectrum of resistance to footrot among sheep. This spectrum includes animals which remain chronically infected and those that do not become infected at all. Intermediate levels of resistance are reflected firstly in the time taken by different groups of sheep, to become affected after exposure and secondly, to heal after becoming affected.     

Transmission of virulent footrot between sheep and goats

OBJECTIVE: To determine the infectivity of ovine and caprine strains of Dichelobacter nodosus for both sheep and goats. DESIGN: Pen experiments in which 20 sheep and 19 goats were challenged directly with the two strains, and transmission experiments on pasture, using donors infected by experimental challenge. RESULTS: Sheep and goat strains of D nodosus infected both animal species in experimental challenges. Animals so infected transmitted footrot to both sheep and goats on pasture plots. A significantly smaller proportion of goats than sheep was infected when challenged with either strain. The interval between exposure and development of footrot in goats was longer than in sheep when recipient animals were exposed to infected donors on pasture. The disease was less invasive in goats than in sheep. CONCLUSIONS: With the strains of D nodosus used there was no evidence of host specificity. Direct transmission of footrot can occur between sheep and goats in the same environment. There is a need to include goats in ovine footrot eradication programs and vice versa.     

Effectiveness of vaccination in controlling ovine footrot

Efficacy of reducing footrot by use of a commercial vaccine was evaluated over 2 yr with 223 ewes from five crossbred genotypes. Ewes were assigned randomly within genotype, age and initial footrot status to a 2 x 3 factorial array of vaccination in the 1st yr and fall vaccination, winter vaccination or control in the 2nd yr. The flock contained a single Bacteroides nodosus serotype (XV) known to be highly cross-reactive with one of the vaccine serotypes (British serotype H). Vaccination reduced footrot incidence by 61% (P less than .01) in the 1st yr and by 45% (P less than .01) in the 2nd yr. Vaccination of previously uninfected ewes did not significantly reduce the rate of new infection, but vaccination of infected ewes reduced re-infection by 92% (P less than .01). Vaccination in the 1st yr failed to produce any carryover or additive protection in the 2nd yr. Genotypes differed in both footrot incidence (P less than .05) and footrot reduction following vaccination (P less than .05), but the effect was inconsistent between years. Vaccination increased serum antibody titers in both years (P less than .01). Among vaccinates in the 1st yr, infected ewes had lower titer levels than uninfected ewes (P less than .01), but no correlation between titer level and incidence was observed in the 2nd yr.     

硫酸锌治疗奶牛蹄底溃疡

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