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This article was published in 1981
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Bacteroides nodosus Vaccines

P.D. Claxton, B.V.Sc., Dip.Bact. (London), Veterinary Research Station, NSW Dept. of Agriculture, Glenfield

The Stock Medicines Boards of Victoria and New South Wales have recently registered a Sheep Footrot Vaccine containing representatives of nine serogroups of Bacteroides nodosus. This vaccine is based on the results of research carried out in the Department of Veterinary Clinical Studies, University of Sydney. The research programme was aimed at investigating the reasons for the apparent lack of efficacy of footrot vaccines when used in Merinos in Australia, despite promising results recorded overseas for monovalent or bivalent alum precipitated (AP) vaccines.

The effect of adjuvant, number and timing of vaccine doses and antigenic differences between vaccine and challenge strains of B. nodosus were examined.

Adjuvant

Under pen challenge conditions it was found that AP vaccines gave little or no protection to Merinos against homologous challenge. The addition of Quil A (a saponin. derivative) to AP vaccines significantly enhanced the antibody response but provided only short-lived (less than eight weeks) protection after a second dose of vaccine.

Oil adjuvant vaccines resulted in more persistent antibody responses but the best results were obtained with a oil adjuvanted AP (APO) vaccines. With such vaccines up to 16 weeks protection against homologous challenge could be obtained after each dose of vaccine. High persistent antibody titres were also recorded.

Number and Timing of Vaccine Doses

The results of some earlier field and pen challenge in trials suggested that significant cross protection occurred using a monovalent type A vaccine. However, following a series of controlled pen challenge experiments it was concluded that protection afforded by APO vaccine was serogroup or serotype specific. A type A vaccine protected sheep against serogroup A challenge but did not protect against seragroup B, C, D, E, F, G or H challenge after one, two or three doses of vaccine.

The timing of the second dose of vaccine depended on the antibody response to the primary vaccination. In general it should be given six to twelve weeks after the primary dose.

Antigenic Differences

Using slide agglutination tests 755 of 762 isolates of B. nodosus from 47 properties could be classified into eight distinct serogroups. These were identified as A to H by extending the classification of Egerton (1973). The existence of these serogroups was confirmed using cross tube agglutination tests and antigens and rabbit antisera prepared from 44 isolates representing the eight serogroups. On the basis of the type of agglutination occurring in the tube agglutination test the grouping was considered to be based on K or pilus antigens.

The existence of subgroups or serotypes within some of these serogroups was confirmed using absorbed antisera and cross tube agglutination tests. At least 16 'serotypes' appear to exist (Table 1).

Individual flocks were found to carry representatives of up to six serogroups of B. nodosus and individual sheep to be infected with up to four serogroups in one foot.

The number of serogroups identified in a particular flock tended to depend on the number of sheep examined and the number of isolates serogrouped from each sheep. It was considered that a minimum of ten affected sheep from a flock should be examined and that ten colonies from each sheep be serogrouped in order to give a reasonable idea of the range of serogroups present.

Approximately 25 per cent of affected feet sampled were found to contain more than one serogroup of B. nodosus.

Implications

Under pen challenge conditions it was found that a vaccine prepared from one serotype, e.g. A₁ would protect against challenge with closely related serotypes, e.g. A₁ and A₂, provided high enough K agglutinin titres were induced. A vaccine prepared from a representative of one serogroup would not protect against challenge with a representative of one of the other seven serogroups.

Under both pen and field conditions it was shown that vaccination may alter the distribution of serotypes of B. nodosus within a flock by providing protection against strains closely related to the vaccine strains but little or no protection against unrelated strains (Tables 2, 3, 4).

It would seem, then, that vaccines for field use should contain representatives of the eight serogroups so far defined. They should also be incorporated in a highly effective adjuvant to induce high persistent K agglutinin titres. A problem still to be overcome is the large local granulomas produced by oil adjuvant vaccines.

There tends to be a lower antibody response to the components of a multivalent B. nodosus vaccine than to the individual components as monovalent vaccines. This is particularly true after the first dose of vaccine. It is, therefore, considered that best results with multivalent vaccines might be achieved by first vaccinating sheep four to six weeks prior to the expected commencement of transmission. Re-vaccination should then be carried out at the first sign of footrot in the flock or, preferably, at the onset of conditions favourable to transmission. The aim of vaccination should be to reduce the incidence and prevalence of footrot to low levels and eliminate residual infection during summer months by traditional methods.

Reference

Egerton, J.R. (1973) Surface and somatic antigens of Fusiformis nodosus. J. Comp. Path. 83: 151-159

TABLE 1

Tube Agglutination Reactions between Bacteroides nodosus isolates and Antisera Prepared in Rabbits

Serogroup
A				B				C	D	E		F		G		H
Subgroup Antiserum
Antigen		A1	A2	B1	B2	B3	B4			E1	E2	F1	F2	G1	G2	H1	H2
Sub-group	Prototype Strain*	1001	1251	1006	1208	1190	1125	1008	1072	1137	1114	1017	1244	1220	1004	1215	1057
A1	1001	10240∂	2560	0+	0	0	0	0	0	0	0	0	0	0	0	0	0
A2	1251	2560	10240	0	0	0	0	0	0	0	0	0	0	0	0	0	0
B1	1006	0	0	10240	10240	1280	1280	0	0	0	0	0	0	0	0	0	0
B2	1208	0	0	5120	10240	2560	320	0	0	0	0	0	0	0	0	0	0
B3	1190	0	0	5120	10240	20480	5120	0	0	0	0	0	0	0	0	0	0
B4	0	0	1125	0	0	5120	1280	5120	20480	0	0	0	0	0	0	0	0
C	1008	0	0	0	0	0	0	10240	0	0	0	0	0	0	0	0	0
D	1072	0	0	0	0	0	0	0	10240	0	0	0	0	0	0	0	0
E1	1137	0	0	0	0	0	0	0	0	10240	2560	0	0	0	0	0	0
E2	1114	0	0	0	0	0	0	0	1280	20480	0	0	0	0	0	0	0
F1	1017	0	0	0	0	0	0	0	0	0	0	20480	320	0	0	0	0
F2	1244	0	0	0	0	0	0	0	0	0	0	320	5120	0	0	0	0
G1	1220	0	0	0	0	0	0	0	0	0	0	0	0	5120	1280	0	0
G2	1004	0	0	0	0	0	0	0	0	0	0	0	0	640	10240	0	0
H1	1215	0	0	0	0	0	0	0	0	0	0	0	0	0	0	5120	640
H2	1057	0	0	0	0	0	0	0	0	0	0	0	0	0	0	320	5120

* Sydney University Department of Veterinary Clinical Studies Culture Collection number.

∂ Reciprocal of agglutinin titre

TABLE 2

Proportion of vaccinated and unvaccinated sheep infected at Inspection 6. Distribution of serogroups of B. nodosus among sampled infected sheep.

					Distribution of Serogroups
Group	Vaccination Status	Number* in Group	Number Infected	Number Sampled	A	B	F	G	H	Mixed Infections
1	Twice	90	25(27.8%)	15	0	2+	0	14	2	2
2	Once	90	36(40.0%)	13	0	4	1	10	0	2
3	Nil	90	47(52.2%)	16	2	11	0	6	1	3

* Number presented for final inspection.
+ Number of animals infected with serotype. Total exceeds number of sheep sampled because of occurrence of mixed infections.

TABLE 3

Expected distribution of serogroups at Inspection 6 in vaccinated and unvaccinated sheep.

				Expected Distribution of Serogroups*
Group	Vaccination Status	Number in Group	Number Infected	A	B	F	G	H
1	Twice	90	25 (27.8)+	0 (0)	3.33 (3.70)	0 (0)	23.33 (25.92)	3.33 (3.70)
2	Once	90	36 (40.0)	0 (0)	11.08 (12.31)	2.77 (3.08)	27.69 (30.77)	0 (0)
3	Nil	90	47 (52.2)	5.88 (6.53)	32.31 (35.90)	0 (0)	17.62 (19.58)	2.94 (3.27)

* Determined by multiplying the observed number by the number infected and dividing by the number sampled.

+ Figures in parenthesis indicate percentages.

TABLE 4

Protection rates afforded by one and two doses of a polyvalent B. nodosus vaccine

Protection Rate %
			By Serogroup
Group	Vaccination Status	Overall	A	B	F	G	H
1	Twice	47	(100)*	90	IS+	0	IS
2	Once	23	(100)	66	IS	0	IS

* Unreliable due to low prevalence of serogroup A strains in control group.

+ Insufficient sample size.

x Determined from expected values (Table 3).