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This article was published in 1982
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Field Experiences With Footrot Vaccine
K.J. Astill, B.V.Sc., ICI Australia Operations Pty. Ltd., SYDNEY NSW
The control of footrot has always been one long slogging field experience, involving a farmer approach varying from treating individual cases, right through the scale of intensive control, to eradication, which may involve a decision to sell the entire flock. The latter decision may appear reckless, but is nevertheless mostly based on sound economics often after consideration, of the owners involvement in other farming enterprises.
No attempt will be made to place a dollar figure on the value of treatment, loss of condition, depressed wool growth, lowered fertility and deaths. Field officers who have been involved in outbreaks in large areas of the state, will know that economic losses due to each of the above are considerable. One can add to these problems the despair of the owner and the fact that neighbours often become enemies.
THE INITIAL INTRODUCTION OF VACCINES
Field Veterinarians with extensive experience in footrot have recognised the value of Beveridge's principles for control and eradication of this disease. This method involving radical paring, very frequent foot bathing, and isolation of infected sheep, demands a very heavy workload from the owner. Increasing labour costs have, over the last ten years lowered the number and quality of station labour, resulting in a decreased efficiency of control.
Such circumstances highlight the need for a vaccine. Following Egerton's work in 1970-1973 the first commercial vaccines were released in 1972 based on the MCMASTER STRAIN. All these were B. nodosus colonies, from a limited number of properties, and the vaccine had been tested on those same properties, i.e. unwittingly homologous vaccines were utilised.
Field results were excellent on some properties, but disastrous on others. Vaccines were withdrawn from sale in 1976.
The most significant experiences resulting from Egerton's research and the field results were:
1. The vaccine would both cure and protect sheep from infection with B. nodosus.
2. The recognition that the bacteriology was very complex.
3. The realisation that a search for more strains of B. nodosus was an urgent priority.
4. Following from the above was the necessity of devising techniques for strain identification.
5. The influence of adjuvants on immunity needed to be determined.
Realisation of the above points finally led to the NSW Department of Agriculture calling meetings in 1976, and 1978.
The second meeting in February 1978 between vaccine manufacturers, the Victorian [and] NSW Department of Agriculture and CSIRO, stimulated renewed interest into research towards the development of footrot vaccines.
Agreement was reached on protocols for trials, and criteria for footrot vaccine registration with the Stock Medicines Board of NSW.
FIELD TESTING OF VACCINES FROM 1978
The following protocols for field trials, accepted by the 1978 meeting, were as outlined below.
CATEGORIES OF INFECTION
+ Some interdigital skin damage
++ Interdigital lesion clearly associated with footrot.
+++ Some under-running of heel and sole.
++++ Some under-running of wall of hoof.
MEASURE OF EFFICIENCY OF VACCINE
a. Level of infection at the commencement of trial should be at least 20%.
b. Cure rate (PER CENT) = 100 - 100 X PERCENT VACCINATES STILL AFFECTED / PERCENT CONTROLS STILL AFFECTED
Measured at 6 weeks after completion of vaccination must be not less than 65%.
c. Protection rate (PER CENT) = 100 - 100 X PERCENT AFFECTED VACCINATES / PERCENT AFFECTED CONTROLS
Measured at 12 weeks after completion of vaccination must be not less than 70%.
INSPECTIONS
a. At Primary Vaccination
b. 6 weeks after completion of Vaccination
c. 12 weeks after completion of Vaccination
TRIAL ORGANISATION
a. Trial properties must be in endemic areas - in summer and winter rainfall areas, and in irrigation areas.
b. Groups of 100 were to be used. Preference was for merinos or comebacks.
c. Vaccinated and control sheep run together.
d. No treatments e.g. paring and footbathing to be carried out.
e. Ten per cent of each group should be bled.
f. Typing of strains to be done at start and end of trials.
RESULTS OF FIELD TESTS
Spring 1978
ICI Tasman prepared a bi-valent vaccine based on CSIRO Strains 198 and 217. (Serotypes A & C) as a result of work published by Egerton in 1973.
This vaccine was tested on properties located near Holbrook (2), Molong, Orange, Young, and two in Victoria, in accordance with the protocols agreed upon from the Departmental meeting.
As with the original vaccine (pre 1976), results were variable with mostly only 55% protection recorded. Overall, the results were unsatisfactory and not up to the standard of the requirements for registration under the Stock Diseases Act.
Conditions for spread of footrot during the trial were excellent.
LESSONS LEARNED FROM THIS FIELD WORK IN 1978
Samples taken from trial properties enabled Claxton, working at the Veterinary School with Egerton, to isolate strains of B. nodosus, and serotype them.
By means of Kagglutination tests, Claxton and Liardet (ICI TASMAN LTD) agreed that strains not only of A, B, C, occurred in the field, but serogroups of D, E, F, were also identified from field isolates.
FIELD TRIALS SPRING 1979
ICI TASMAN prepared a 5 strain vaccine for field trials containing serogroups A, B, D, E, F. C strain was excluded because it was rarely seen in the field.
Initial pen trials conducted prior to its use, showed on challenge that the vaccine protected against, and assisted in the improvement of clinical footrot with strains A, B, D and E. Results of strain F were invalidated due to an intercurrent infection with an unrelated type in Vaccinates and controls.
Once again the season favoured the rapid spread of footrot, but the change in field results from the previous year, was spectacular on four properties in NSW and two in Victoria.
RESULTS
| TRIAL | New South Wales | Victoria | ||||
|---|---|---|---|---|---|---|
| 1 | 2* | 3 | 4 | 5 | 6 | |
| CURE RATE 6 Weeks | 79 | 46 | 89 | 80 | 66 | 100 |
| CURE RATE 12 Weeks | 92 | N/A | 90 | 79 | 67 | 100 |
| PROTECTION RATE 6 Weeks | 77 | 80 | 92 | 79 | 82 | 90 |
| PROTECTION RATE 12 Weeks | 94 | (84) | 92 | 79 | 81 | 100 |
* Controls withdrawn from paddock at about 8 weeks - and treated and footbathed to stop deaths.
In trial 5, an extra group treated by weekly footbathing, showed a nil cure rate at 6 and 12 weeks, with a protection rate at 6 and 12 weeks of 7% and 19% respectively.
These results were more than adequate for registration under the protocols.
During the period of the trials, further serogroups were identified. The final commercial vaccine, released to the farmers in June 1981, contained Strains A, B1, B2, C, D, E, F, G, H.
FIELD EXPERIENCES WITH THE VACCINE
Since the release of the Vaccine to the farmer only five properties have shown up as problems. Sheep owners in general have put the vaccine under pressure by many means. Apart from these five properties, users have been well satisfied, e.g. vaccination at the point of lambing, when the disease was spreading rapidly, was used without loss of ewes or lambs. The owners wondered whether the second Vaccination was really necessary!
COMPLAINT PROPERTIES
Results can be summarised as follows:
1. All complaints arose from the first commercial batch (Batch 152).
2. This batch is far more sensitive to high and low environmental temperatures, than is the case with subsequent batches, or with Clostridial Vaccines.
3. Properties were located at Harden, Stockinbingal, Wombat, Illabo and Holbrook.
4. Vaccine remaining in the field was withdrawn from stockists (Batch 152).
5. All strains recovered from the properties were present in the Vaccine.
6. Serology indicated some low titres. As a result, all Vaccinated sheep were given a booster dose, which is being monitored.
7. On almost all properties, Vaccination commenced when the challenge was extremely high.
8. It appears likely that all the problems were due to lack of care in handling of the Vaccine in spite of warnings on the label.
COMMENTS ON SEROLOGY
Victorian Trial 1981-1982
Batch 152 was used in the Victorian Trial which commenced in November 1981. Titres measured 6 weeks post second injection were quite satisfactory.
TESTS ON A BROKEN EMULSION (Batch 152)
These have indicated that titres are quite satisfactory. However, in the field, adequate shaking would be necessary.
SEROLOGY AS A MEASURE OF PROTECTION
It has not yet been established that definite levels of serological response can be directly related to cure or protection with footrot vaccine. Sufficient observations have been made, which confirm that there is very little serological response to natural infections of footrot.
INFLUENCE OF FOOTROT CONTROL PROCEDURES ON FOOTROT CONTROL
A co-operative trial has been conducted by the Department of Agriculture Victoria and ICI, comparing the effects of Vaccination, Vaccination plus footbathing, footbathing and paring, and no treatment, (TRIAL MATERIAL COMMERCIAL BATCH 152).
RESULTS
| GROUP | PERCENT INCIDENCE OF FOOTROT AT | CURE RATE | |||
|---|---|---|---|---|---|
| 4/11/81 | 15/12/81 | 28/1/82 | 18/3/84 | 28/1 | |
| CONTROL | 25 | 29 | 35 | 4* | |
| VACCINE & FOOTBATH | 19 | 4 | 2 | ? | 90% |
| VACCINE ONLY | 22 | 15 | 8 | ? | 64% |
| FOOTBATH & PARING ONLY | 25 | 19 | 19 | 17 | 24% |
* FEET PARED AND SHEEP VACCINATED AT 28/1/82.
CONTROLS AND VACCINE ONLY GROUPS RUN TOGETHER.
TWO FOOTBATHING GROUPS RUN TOGETHER.
FUTURE DEVELOPMENT IN FOOTROT VACCINES
Research towards improving the Vaccine could be directed into the following problems:
1. ADJUVANTS - Results show that oily adjuvants produce the best antibody levels for the longest period. Their problem is in the production of a significant number of local reactions.
Hopefully a new adjuvant will be found which will produce equal or better immunity with minimal skin reaction.
2. ANTIGENS - Antigenicity has been found to be due to the high pilus numbers, and work is proceeding on the use of pure pilus vaccines, as opposed to conventional whole cell vaccines. Success is related to the availability of isolates from the field, their successful transport to the laboratory, resulting in a better selection of highly piliated strains.
3. EPIDEMIOLOGY OF STRAINS OF FOOTROT - The number of new strains now recovered and identified over the last few years, poses the problem of lack of knowledge of the persistence of each strain both in the foot and in the paddock.
I am sure that the claims of some experienced and knowledgable sheep owners, that footrot spreads on their properties during periods of frost, on the one hand, and midsummer on the other, should not be ignored.
4. B. nodosus SEROGROUPS - Field work has shown over the last footrot season that no new strains have been uncovered. This should give field veterinarians confidence that the vaccine gives extremely good coverage.
Continual monitoring is still necessary as the control of nine strains may tend to select new strains. If these are around, they must be extremely rare.
SUMMARY
The background of the development of the footrot Vaccine manufactured by ICI TASMAN UTD is outlined.
The influence of strains of B. nodosus on the results of vaccination in the field are discussed, while suggestions for future research are suggested.
ACKNOWLEDGEMENTS
The author wishes to acknowledge the advice, assistance, and devotion of Dr. Peter Claxton and his staff and Prof. Egerton and his staff at Camden, in the development of a footrot vaccine.
Personal communications from D. Liardet and staff at ICI Tasman Ltd. have been freely used.
Thanks are due to the Divisional Veterinary Officers and Veterinary Inspectors who have collected specimens and sera when the author has not been available.
Finally, it should be recognised that this development work was the result of a joint project with the Department of Agriculture NSW, the Sydney University Veterinary School, CSIRO and ICT Tasman Ltd.
REFERENCES
Department of Agriculture NSW (28/2/78) - Minutes of Meeting to discuss Footrot Vaccines
EGERTON, J.R., BURRELL, D.H., (1970) - Australian Veterinary Journal 46 : 179
EGERTON, J.R., ROBERTS, D.S., (1971) - Journal of Comparative Pathology 81 : 170
EGERTON, J.R., THOMPSON, J.J., MERRITT, G.C., (1979) - Veterinary Record 104 : 98
STEWARD, D.J., (1978) - Research in Veterinary Science 24 : 293
UNIVERSITY OF SYDNEY (1981) - Report of workshop - Ovine Footrot.