Efficacy of a multivalent Bacteroides nodosus vaccine against foot rot in sheep in Britain

A multivalent Bacteroides nodosus foot rot vaccine was tested by comparing the prevalence of foot rot in 317 vaccinated ewes and lambs with the prevalence in 422 unvaccinated control sheep. The vaccine conferred statistically significant protection against foot rot. The vaccine also demonstrated a therapeutic effect in animals with foot rot, after one injection.     

Comparison of treatment methods for the control of contagious ovine foot rot

Four methods of treatment for ovine foot rot were evaluated: foot trimming and topical treatment (brief, daily foot bathing in 10% zinc sulfate); vaccination with an oil-alum adjuvanted, multivalent, Bacteroides nodosus bacterin, vaccination with the bacterin plus foot trimming and brief foot bathing, and 1-hour 10% zinc sulfate foot soaks. Compared with results of sheep in a nontreated control group, vaccination reduced the number of infected feet by 8%. Daily walk-through foot bathing reduced the number of infected feet by 16%, and vaccination and foot bathing reduced the number by 27%. In another experiment, treated but nonresponsive sheep were subjected to 2 one-hour foot soaks in 10% zinc sulfate. Compared with results in nontreated controls, the soaks reduced the number of affected sheep by 58%. Previously nontreated sheep responded with a 69% reduction of affected animals over controls.     

Electron microscopic study of Bacteroides nodosus pili and associated structures.

Surface structures of Bacteroides nodosus were examined by electron microscopy. Collodion film and chrome shadowing were used for maximizing the visualization of B nodosus pili and ring structures. The existence of B nodosus pili in foot rot lesions was confirmed. Contrary to previous reports, it was found that B nodosus pili production can be retained through serial broth transfer under certain conditions. Capsule production by B nodosus was irregular in that it could be either lacking or variable in thickness. A bacteriophage capable of infecting B nodosus also was detected.     

Antibody responses of sheep vaccinated with foot rot vaccines

Enzyme-linked immunosorbent assay (ELISA) and crossed immunoelectrophoresis (IEP) were used to investigate antibody responses of sheep vaccinated with a double adjuvanted or single adjuvanted commercial foot rot vaccine. ELISA detected an antibody response of greater magnitude to the double adjuvant vaccine compared with the single adjuvant vaccine. Sera from sheep vaccinated with double adjuvant vaccine recognised at least six antigens of Bacteroides nodosus in crossed IEP while sera from the single adjuvant vaccinated sheep recognised one antigen. The use of non-denatured antigens of B nodosus in ELISA and crossed IEP enabled quantitative comparisons of antibody responses to the different foot rot vaccines to be made.     

Genetic-associated resistance to foot rot in selected Targhee sheep

Three Targhee rams obtained from the Ohio Agricultural and Experimental Station had been identified as foot rot resistant on the basis of results of challenge exposure. In the first breeding trial, when rams were bred to 20 foot rot-susceptible ewes, the percentages of foot rot-resistant offspring from the 3 foot rot-resistant rams were 68, 82, and 100, compared with 55 and 60 for foot rot-resistant offspring from 2 known foot rot-susceptible rams. In the second year, the foot rot-resistant rams were mated with ewes of unknown foot rot status. The foot rot-resistant status of their lambs was compared with that of range-raised lambs whose parents' foot rot status was unknown. During the first year, challenge exposure to the disease consisted of confinement of the lambs in moist or wet pens with sheep affected with the naturally acquired disease. This protocol was repeated for lambs born during the second-year breeding trial. In addition, the right front foot of each lamb was inoculated with a broth culture of Bacteroides nodosus. During the second year, when data that included infected feet from all lambs were analyzed, 41% of the progeny of the foot rot-resistant rams and 17% of the offspring of parents of unknown foot rot status were unaffected by the disease. When the B nodosus-inoculated foot was not included in the analysis, however, 61% of the progeny of the foot rot-resistant rams and 29% of the others were unaffected. The resistance to foot rot undoubtedly is hereditary. The mechanism of resistance may be in the interdigital skin.(ABSTRACT TRUNCATED AT 250 WORDS)     

An economic evaluation of various treatments for contagious foot rot in sheep, using decision analysis

Two decision analysis models were constructed to identify the cost-effectiveness of treatment and/or prevention regimens for ovine foot rot through a systematic evaluation approach of 2 consecutive phases. The first model evaluated the cost-effectiveness of examining the sheep for foot lesions and the use of 1 of 32 treatment regimens when lesions were present. The second model evaluated the 6 most cost-effective treatment regimens from the first model with or without a preventive measure (in this case, vaccination) to determine the most cost-effective approach to preventing/treating foot rot in a single year. Three prevalence levels of foot rot were used. In addition, 3 levels of reduced production attributable to foot rot were used. Threshold analysis, a form of sensitivity analysis, was used to evaluate allowable variations in the success rates and cost of treatments/prevention where the outcome of the models remains unchanged. Of the 32 treatment regimens tested in this model, the use of 10% zinc sulfate applied to the feet of sheep with foot rot was the most cost-effective regimen, regardless of the prevalence levels of the disease or its impact on productivity. In the second model, the use of vaccination with paring of the feet, as a preventive measure, followed by a treatment of the sheep that were still infected, was less cost-effective than to treat only the sheep with foot lesions and disregard prevention. This was true regardless of the prevalence levels of the disease or its impact on productivity.     

Comparison of alum-absorbed or non-alum-absorbed oil emulsion vaccines containing either pilate or non-pilate Bacteroides nodosus cells in inducing and maintaining resistance of sheep to experimental foot rot

Highly pilate (P) or non-pilate (NP) cells of Bacteroides nodosus were compounded into oil emulsion (O) either with or without prior absorption onto alum (A). The abilities of these four preparations (referred to as PAO, NPAO, PO and NPO vaccines) to stimulate antibody production and to protect sheep from foot rot were compared. Two injections of PAO vaccine protected sheep against homologous challenge 12 weeks after the second dose by PO, NPO and NPAO vaccines were less effective. Sheep were protected against homologous challenge for 14 weeks after a single dose of PAO vaccine and for 22 weeks after three doses; an ameliorative effect was still evident 40 weeks after the third dose. Protection against challenge with two heterologous strains was demonstrated at six weeks after three doses of vaccine. A numerical system of scoring the lesions also confirmed that foot rot in vaccinated sheep challenged outside the 'protective' period of the vaccine was somewhat less severe than in controls. PAO vaccine induced much higher and more persistent titres of agglutinins than the other vaccines tested. There was a relationship between agglutinin titres and resistance to homologous challenge.     

Purification, characterization, and serologic characteristics of Bacteroides nodosus pili and use of a purified pili vaccine in sheep

Hair-like appendages (pili) were isolated and purified from Bacteroides nodosus, the etiologic agent of foot rot disease in sheep. Microscopic and biochemical analyses indicated that pili from organisms isolated in Australia, New Zealand, and the United States are morphologically and structurally similar. Pili are filamentous assemblies of identical protein subunits. Using specific antisera raised in rabbits against pili, 7 antigenic types were identified. A geographic pattern in the distribution of the pilus serotypes was not evident. In a preliminary vaccine trial, sheep vaccinated with purified pili developed resistance to challenge exposure to B nodosus. Protection was correlated positively with the serum anti-pilus antibody titers.     

Isolation and identification of anaerobic bacteria from ovine foot rot in Spain

A microbiological study was made of 125 Merino sheep showing clinical signs of foot rot. A total of 435 strictly anaerobic strains were isolated, belonging to the following genera: Bacteroides, Peptostreptococcus, Tissierella, Fusobacterium, Megasphaera, Eubacterium, Acidaminococcus, Clostridium, Peptococcus and Propionibacterium. Of the 35 species obtained, the following were found in more than 10 per cent of animals sampled: Bacteroides nodosus, B putredinis, B buccae, B ruminicola subspecies brevis, Tissierella praeacuta, Peptostreptococcus anaerobius and Megasphaera elsdenii. Six culture media were used for isolation. Agar brucella and agar brucella enriched with G-N anaerobe supplement proved to be the most efficient for isolating anaerobic bacteria.     

Identification and genetic mapping of proteins encoded in the fimbrial subunit gene region of Bacteroides nodosus

The fimbriae produced by the anaerobic bacterium Bacteroides nodosus are important in the pathogenesis of ovine foot rot. Studies on other microorganisms have shown that the genes coding for the production and assembly of fimbriae are often clustered. By the use of maxicells, transposon mutagenesis and expression vectors, we have identified several genes which are located in the fimbrial subunit gene region. Antiserum was prepared against one of the proteins (88 kDa) which we were able to overproduce in Escherichia coli. In Western blots, these antibodies reacted with an 88 kDa protein located in the B. nodosus cell membrane. However, they did not react with the putative basal protein which is found in fimbrial preparations. We concluded that in B. nodosus the genes involved in fimbrial assembly are not all localised to one small region of the genome. In addition, our studies showed that although the fimbrial subunits are not assembled into intact fimbriae, an N-terminal sequence is processed in E. coli.     

The use of an autogenous Dichelobacter nodosus vaccine to eliminate clinical signs of virulent footrot in a sheep flock in Bhutan

An outbreak of virulent footrot was investigated in a flock of 605 Merino cross-bred sheep in Bhutan. Conventional control methods in the preceding eight years had reduced its prevalence from 36-79% in different components of the flock to about 15% overall. Only one serogroup (B) of Dichelobacter nodosus was identified among 40 isolates cultured from affected sheep. A vaccine prepared from this strain was used in a pilot trial to compare the response of 14 treated and 14 untreated sheep. All affected, vaccinated animals in this trial healed quickly and were protected against re-infection while additional cases developed among untreated sheep during a period favourable for the spread of footrot. The serogroup B vaccine was administered to the whole flock for two successive years. No other footrot treatment was given during these or subsequent years. The whole flock was examined three times, foot by foot, for two years and twice yearly for another two years. When vaccination began there were 88 affected sheep in the flock, an affected sheep being defined as an animal with a foot-score of 2 or greater in one or more feet. There were neither affected sheep in the flock 30 days after the first dose of vaccine nor were any identified in later inspections. Virulent footrot, originating from the farm under investigation, persisted in neighbouring village flocks during this period. It was concluded that whole flock specific D. nodosus vaccination made a major contribution to the elimination of all clinical signs of footrot from the flock of 605 sheep where the condition had previously persisted for 10 years.     

Humoral responses to a multivalent vaccine in age-matched lambs of different bodyweight and nutrition

K-agglutination, pilus-enzyme-linked immunosorbent assay (ELISA) and outer membrane protein-ELISAs were used to assess humoral responses after vaccination with a commercial, multivalent, ovine foot rot vaccine (Dichelobacter nodosus whole cells) in three groups of nine-month-old lambs of markedly different bodyweight, nutritional history and dietary protein supply. Mean bodyweights of lambs in low (L), medium (M) and high (H) bodyweight/nutrition groups were 22, 32 and 48 kg, respectively, at the time of vaccination. Few significant differences in humoral responses to vaccine antigens were found between groups. However, lambs in group H tended to have lower levels of antibody to a greater number of component antigens than did lambs in the other groups. These results suggest that low bodyweight due to poor nutrition is unlikely to affect the response of sheep to multivalent foot rot vaccines.     

Effect of pilus dose and type of Freund's adjuvant on the antibody and protective responses of vaccinated sheep to Bacteroides nodosus

Groups of sheep were immunised twice with one or other of six vaccines consisting of purified pili from Bacteroides nodosus at three dose levels (10, 38 and 154 micrograms) and emulsified with either complete (CFA) or incomplete Freund's adjuvant (IFA). Beginning one month after vaccination the sheep were homologously challenged on irrigated pasture, with naturally transmitted foot rot for a period of 26 weeks. Statistical analyses of the number of feet per sheep with severe foot rot demonstrated that there was a significant effect of vaccinal dose but neither an adjuvant effect nor an interaction between dose and adjuvant. Similar conclusions were reached when the titres of antipilus agglutinins in the serum were analysed. By both criteria the responses to doses of 154 and 38 micrograms of pili were significantly better than to 10 micrograms, but not significantly different from each other. The IFA vaccines caused less reaction at the sites of injection than the CFA vaccines and within the former the vaccines containing 10 and 38 micrograms pilus produced less reaction than those containing 154 micrograms. Hence a vaccine containing 38 micrograms of purified pili in IFA is nearly optimal for homologous protection against severe foot rot and is acceptable in terms of the reaction at the injection site.     

Advances in the control of foot rot in sheep

All cases of foot rot, whether acute, chronic, benign, or inapparent, must be identified. If the outbreak is severe and production losses warrant, each foot of each animal must be examined thoroughly. Proper handling facilities and equipment, adequate light, and dry working conditions are needed to properly examine each foot. Infected sheep must be separated from the clean flock. Following extensive treatment, these animals must be diagnosed as free from the disease before returning to the clean flock. Animals that do not respond must be culled from the flock. Although copper sulfate and formalin are effective materials for footbathing, zinc sulfate is equally effective and does not irritate the skin, eyes, or lungs as does formalin, or stain the wool as does copper sulfate. A 10% zinc sulfate solution with a nonionic surfactant is an effective footbathing or foot soaking solution. The cure rate is improved by a thorough foot paring and a foot soak of at least 30 minutes. A number of treatment options along with formulations are outlined in the 1988 edition of the Sheep Production Handbook of the Sheep Industries Development Program, Inc, 6911 Yosemite, Englewood, CO 80112.     

Colostral transfer of Bacteroides nodosus antibodies in sheep.

Ovine contagious foot rot may cause lameness in sheep, resulting in decreased wool growth and low weight gain. Affected neonatal lambs are difficult to treat, and treatment is labor intensive; thus, a method of prevention is warranted. Vaccination of ewes with a multivalent vaccine in an oil adjuvant induced development of antibody to the somatic O antigen of Bacteroides nodosus, and this antibody was detected in serum of newborn lambs after consumption of colostrum from the vaccinated ewes. Antibody titers were determined in 48 unvaccinated ewe/lamb pairs, and in 50 once-vaccinated and 78 twice-vaccinated pairs. Serum and colostrum O-agglutinin titers to B nodosus were determined by a microtitration agglutination test. Lambs from vaccinated ewes had significantly (P less than 0.05) higher O-agglutinin titers than those from unvaccinated ewes, and double vaccination of ewes resulted in the highest potentially protective titers (greater than 1:2,400) in ewes and lambs.     

A comprehensive review of ceftiofur sodium and hydrochloride formulations for treatment of acute bovine foot rot

Seven well-controlled studies conducted under multiple management conditions demonstrated that ceftiofur, a late-generation veterinary parenteral cephalosporin, is effective for the treatment of bovine foot rot in beef and dairy cattle. Two preliminary dosage titration studies using a challenge model compared the efficacy of ceftiofur (1.1 mg or 2.2 mg ceftiofur equivalents [CE]/kg administered once daily for 3 days) with placebo. One preliminary clinical study evaluated the efficacy of ceftiofur sodium (1.0 mg CE/kg once daily for 3 days) in lactating dairy cows. Two clinical trials evaluated the efficacy of ceftiofur sodium versus placebo for naturally occurring foot rot, and two trials compared the efficacy of ceftiofur sodium or hydrochloride (1.0 mg CE/kg) with oxytetracycline (6.6 or 10 mg/kg), each administered once daily for 3 days, for treatment of acute foot rot in beef cattle. All trials demonstrated the efficacy of ceftiofur for treatment of acute bovine foot rot. Ceftiofur and oxytetracycline were comparable in efficacy, with ceftiofur having excellent injection-site tolerance and short or no milk discard or preslaughter withdrawal.     

A field trial to assess the therapeutic and prophylactic effect of a foot rot vaccine in sheep

An 18-week field trial was conducted on a sheep ranch to evaluate the therapeutic and prophylactic effect of a commercial foot rot vaccine. Two hundred sheep were included in the study, 100 with detectable foot rot lesions and 100 without. Approximately 50 sheep from each group were selected randomly and vaccinated twice against foot rot at a 6-week interval in the late spring 1984; the remaining sheep acted as nonvaccinated controls. Therapeutic effect of the vaccine was demonstrated by a cure rate of 53% in vaccinated, foot rot-affected sheep vs a cure rate of 19% in nonvaccinated, foot rot-affected sheep. Prophylactic effect of the vaccine was demonstrated by a foot rot prevalence at the end of the 18-week period of 9% for vaccinated sheep vs 53% for nonvaccinated sheep. Associations of foot rot lesions and vaccination with body condition were found to be significant, as was the association between foot rot lesions and mortality.     

The detection and characterisation of Dichelobacter nodosus from cases of ovine footrot in England and Wales

Footrot, caused by the strictly anaerobic bacterium Dichelobacter nodosus, is the most common cause of lameness in sheep in Great Britain but problems exist in association with its diagnosis and control. The fastidious nature of D. nodosus means that complex media and several weeks are required for characterisation. An alternative method to simplify and enhance the detection of D. nodosus in clinical samples is therefore highly desirable. In terms of control, anecdotal evidence from the farming community suggests that the commercially available vaccine, based on Australian isolates of D. nodosus, is not widely employed in this country due to its perceived inefficacy. Seven hundred and six isolates, collected from outbreaks in England and Wales, were therefore used to investigate these issues. A 16S rRNA PCR was adapted to detect D. nodosus in clinical material within 1 day of sampling; a 15% increase in detection compared with culture and less than 1% false negatives were achieved. This represents a major advance in the rapid diagnosis of footrot and will be of great value to practitioners and diagnostic laboratories. Bacterial virulence was tested using protease thermostability and zymogram assays, whilst serogrouping was performed by slide agglutination. All isolates demonstrated virulence patterns previously recorded in Australia and all nine serogroups of D. nodosus (A-I) were represented. Serogroup H was predominant. There was, therefore, no evidence for the presence of novel strains of D. nodosus compared with Australia suggesting the need for further investigation into farmers' views on the use of the commercial vaccine in Great Britain.     

Importance of pilus-associated antigen in Bacteroides nodosus vaccines

The performances of two cellular vaccines, one sparsely piliated and the other well piliated, were compared on irrigated pasture with those of vaccines containing their respective, purified pili. There were statistically significant differences among the four vaccines in the mean numbers of feet per sheep which developed severe foot rot during 27 weeks of exposure. The incidence of severe foot rot was significantly lower in the two pili-vaccinated groups than in the group vaccinated with well-piliated cells, which were in turn substantially more effective than the sparsely piliated. However, the two pili vaccines did not prevent infection of the interdigital skin so that the differences in vaccine performance were much less marked when interdigital skin lesions were included. The number of feet affected by blowfly strike was closely associated with the presence of the most severe lesions and consequently there were far fewer struck feet in the two pili vaccine groups than in the two cellular vaccine groups. Analysis of serum agglutinin titres led to the same assessment of vaccinal efficacy as that derived from the analysis of severe foot rot lesions. Individually the agglutinin response to vaccination was not universally associated with resistance or susceptibility to severe foot rot but mean titres were significantly higher in the two pili vaccine groups than in the highly piliated-cell vaccine group, which were all in turn significantly higher than in the poorly piliated-cell vaccine group.     

奶牛腐蹄病的分析与防治

对蚌埠蚂蚁山奶牛场奶牛腐蹄病发病情况进行了分析研究。结果表明,产奶牛1～≥6胎次腐蹄病的奶牛发病率分别为26．09％、27．64％、60．56％、68．09％、73．08％和81．25％,病蹄发病率分别是7．61％、8．13％、18．31％、23．40％、23．08％和23．44％,且3胎以上牛发病率明显大于1、2胎牛。就发病程度而言,1～5胎次间随着胎次的增加“中~ 、重”程度发病所占比例有逐渐加大的趋势,而“轻”程度发病呈现逐渐降低的变化;而6胎以上牛发病程度的变化与前者相反。