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This article was published in 1959
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Ovine Brucellosis
J. C. KEAST, B.V.Sc., Principal Veterinary Research Officer, Glenfield.
DEFINITION
Ovine Brucellosis, like Brucella infections in other animals, is primarily an infection of the genitalia of both rams and ewes. In the ram it is responsible for lesions of epididymitis; while the primary infection in the female is diseased foetal membranes with subsequent abortion or neo-natal loss of the lambs.
OCCURRENCE AND INCIDENCE
The earliest cases of epididymitis recorded in Australia were by Gunn in 1942, during his studies on fertility in rams. Though the cause was not ascertained at the time there is little doubt that a good proportion of the lesions described by him were due to Brucella infection. Epididymitis was the most common abnormality observed in the rams by Gunn and over 5 per cent. of 9,000 rams examined in Queensland and New South Wales showed lesions of epididymitis.
Moule in 1950 recorded an incidence of 18 per cent. of epididymitis in approximately 1,000 Merino rams examined in North West Queensland but infective agents could not be recovered constantly from lesions. This high figure has not been supported by other Australian workers; who agree more closely with the incidence mentioned by Gunn. Thus Miller considered 6 per cent. over-all incidence of epididymitis in Queensland a more accurate figure; Doolette recorded 7.5 per cent. incidence in 3,000 rams examined in 100 flocks in South Australia; while Osborne working in northern New South Wales found 5.3 per cent. of 4,500 rams affected.
The typically diseased foetal membranes of Brucella infection were first recognised in New Zealand in 1950, and two years later McFarlane and others described the infective agent found in such cases; and also an identical organism found in a number of sites in rams affected with epididymitis. The identity of the organism was not clarified until Simmons and Hall in Queensland and Buddle from New Zealand published their work in 1953, suggesting it to be a "Brucella-like Organism" or a "Brucella Mutant" respectively. It has since been named Br. ovis, though some authorities are still of the opinion that it should not be included in the Brucella genus.
The disease appears to be widely distributed and of considerable economic importance in New Zealand. Besides being responsible for lesions of epididymitis and ram wastage, the disease in the ewe is also important and Brucellosis is one of the major infective agents causing abortion and neo-natal loss in the Dominion. In the United States the disease was reported in 1956 affecting rams in California and although 27 per cent. of 1,882 rams were found affected, the disease was not considered to be a major actor in reducing ram fertility in commercial flocks as assessed by lambing percentages.
In Australia, although epididymitis of Brucella origin is quite common in most of the States. Brucella abortions have been recorded only from South Australia; and only from a limited number of ewes there. In fact, despite the high incidence of the disease in many ram flocks, its effects on lowered lambing results is not always apparent and is confined mostly to stud properties. Abortions and neo-natal losses in lambs are a feature of many lambing flocks in Australia and must not be considered an indication of ewe infection. Examination of foeti from flocks, in both Victoria and New South Wales, with a high incidence of epididymitis in the rams have proved negative for Brucella on cultural examination.
There has been no organised attemnt to determine the incidence of the disease throughout the whole of New South Wales and the only information available is that supplied by field officers with specimens to the laboratory for examination from flocks where the disease was suspected or clinically present. Generally there is little accurate information on the presence of the disease in the large Merino flocks in this state, but opportunity to examine large numbers of these rams has not been provided. A considerable number of Merino rams from this State sent to Queensland ram sales have been culled for epididymitis; so presumably the disease is present to an unknown extent in some Merino studs. On the other hand, less than 4 per cent. of a small sampling of rams from at least three recognised studs were found with lesions; while only one of fifty Merino rams has been proved infective by serological means.
In some of the other breeds in this state the incidence is extremely high. Dorset Horn rams have become very popular in the last ten years as sires of fat lambs and there has been a considerable increase in the number of young studs formed. The incidence of Ovine Brucellosis in this breed is high and has been confirmed serologically or culturally on no less than twenty-four properties. Opportunities to examine rams of other breeds have been limited but indications are that the disease may be widespread in most other British Breeds as indicated in the following Table.
BREED INCIDENCE OF OVINE BRUCELLOSIS IN SUSPECTED INFECTED FLOCKS IN N.S.W. SINCE 1957
| Breed | Properties Examined | Affected | Rams Examined No. | Serologically Reactors |
|---|---|---|---|---|
| Dorset Horn | 29 | 24 | 606 | 153 |
| (Property A | 158 | 22) | ||
| (Property B | 174 | 0) | ||
| (Remaining | 274 | 131) | ||
| Corriedale | 5 | 4 | 145 | 46 |
| Southdown | 3 | 3 | 21 | 5 |
| Border Leicester | 2 | 1 | 6 | 2 |
| Romney Marsh | 3 | 2 | 29 | 5 |
| Cheviots | 3 | 2 | 28 | 13 |
| Merinos | 6 | 1 | 50 | 1 |
| Breed not Specified | 5 | 2 | 32 | 6 |
Properties include both Studs and Commercial Flocks.
LESIONS AND PATHOLOGY
In the female the lesions are confined to the foetal membranes and this may have the effect of causing late abortions (within a month of lambing) or weak lambs that die within a day or two of birth. However, many lambs from infected ewes survive. The early lesions consist of gross gelatinous oedema of the foetal membranes, which may be up to 3 cm. thick; while in advanced cases there are dirty white plaque-like thickenings which have a tendency to coalesce, giving the membrane the appearance of chamois leather. The cotyledons are enlarged, firm, yellowish-white and necrotic instead of the more pliable deep red of normal cotyledons. As stated earlier, ovine Brucella abortions have not been confirmed in this state from the limited number of examinations made to date.
In the ram, epididymitis is the characteristic lesion and in the vast majority of cases the tail of either one or both epididymes may be involved (80-90 per cent.). When the lesions have reached the stage of being clinically palpable they usually are advanced and a considerable deposition of fibrous tissue is responsible for the denseness or firmness of the epididymis.
The earliest lesions are perivascular oedema and proliferation of the epithelium of the epididymis; with a lymphocytic infiltration and occlusion of the lumen of the epididymis. The passage of the spermatozoa is then prevented; causing a spermatocele and sometimes orchitis. Inflammation processes continue and a chronic lesion with deposition of fibrous tissue occurs. If the head and body of the epididymis become involved, or often when the lesion in the tail is extensive, atrophy of the involved testicle is not uncommon.
The enlargement of the tail may be barely palpable or up to a fourfold increase in size and with often an irregular contour. On incision, the affected epididymis will show an increase in white connective tissue in which there may be single or multiple abscess-like spermatoceles containing creamy or caseous material.
Lesions of epididymitis and orchitis, whether of Brucella origin or not, adversely affect the fertility of the ram and marked degenerative changes are apparent in the semen. Deterioration in semen morphology is apparent before clinical lesions appear. In some rams with unilateral lesions the seminal picture may improve after variable period and the rams show a high degree of fertility, but with bilateral lesions the rams are usually sterile.
EPIDEMIOLOGY AND FACTORS ASSOCIATED WITH SPREAD OF THE DISEASE
Ewes - Many flocks of ewes which are or have been affected, are normally fertile. The role of the ewe in spreading infection does not seem to be an important one except for assisting ram to ram infection at mating time. The per cent. of ewes infected during natural mating with infected rams is small and while many of them pick up only a temporary infection which may disappear after few months, a very small number may continue to react serologically for some years. Organisms may be secreted in milk for varying periods in some infected ewes.
Lambs from infected mothers frequently react serologically as a result of placental transmission or colostrum transmission of antibodies but such reactions do not persist for more than two to three months and there is no positive proof that such lambs will develop the disease. However, it still is suspected that this type of infection occurs in a small minority of cases.
The spread of the disease through ram flocks varies considerably and appears to be influenced by husbandry methods. There is no direct evidence that ingestion of contaminated pastures is responsible for the spread of the disease, while mating with infected ewes does not result in ram infection. Much infection in ram flocks is direct from ram to ram or indirect through ewes when the same ewe would be first mated to an infected ram and then to a clean ram during the same heat period. However, high infection rates in young unmated rams are not easily accounted for even though acts of sodomy and suckling are common the initial entrance of infection must be explained.
In view of the fact that the organism has been recovered from the seminal vesicles as well as from the semen, epididymes, testes and regional lymph glands, it is obvious that the vasectomised ram can be an important source of infection and any control measures should consider the "teasers" as well.
DIAGNOSIS
All cases of epididymitis in rams are not of Brucella origin, while all rams infected with Brucella do not develop genital lesions. One authority states that 12 per cent. of infected rams do not develop lesions. These two facts complicate control measures on any one property when eradication measures are being considered. Experience in this state suggests that where lesions exceed, say, 5 or 10 per cent. of a ram flock, then Brucella is most likely responsible; whereas non-Brucella lesions commonly are seen where the incidence is less than 2 or 3 per cent. It is not possible to decide from a clinical examination whether the genital lesions are those of Brucella or not; except in the case of Corynebacterium pyogenes infection of the genitalia where frank pus formation, sinus formation and discharging abscesses are characteristics.
The most exact diagnosis can be made by cultural or smear examination of the semen, but this is not always practical when larre numbers of rams are to be examined; while some infected rams do not secrete organisms regularly in their semen and might be falsely classed as negative. The application of a satisfactory blood test was investigated by a number of investigators, and finally South Australian workers developed the complement fixation test, which has given very useful results. The same type of test was developed also in Vicoria and is being employed in this State, but other workers still regard this serological test to be in the "experimental stage"; maintaining that the test will not indicate all infected rams. Our experience to date has been limited to observations over a few months but these, together with tests kindly carried out for us earlier by Adelaide and Victorian workers, suggest that the complement fixation test is a very useful method to assist in diagnosing and controlling the disease in a flock.
CONTROL
Four main aspects of control will be considered, namely:—
- Manual examination.
- Segregation of various age groups; particularly young rams.
- Use of the complement fixation test.
- Vaccination.
Despite the two important facts mentioned earlier under diagnosis clinical examination of rams and the culling of those with lesions will reduce infection materially in a ram flock. In at least one flock, with admittedly a low incidence of about 3 per cent. cases of epididymitis annually, this method alone would appear to have eradicated the disease. It must be remembered, however, that some of the rams culled in this manner may not necessarily have been infected with Brucella.
Segregation of the young from mature rams is essential if the spread of the disease is to be reduced, as it is frequently the practice to hold rams of all ages in a common ram paddock when not joined with the ewe. Ram lambs must be kept to themselves following weaning and must not have access to other rams which may be infected; even for short periods such as yarding or subsequent mating. The use of young clean rams and older rams on the one flock of ewes is one of the best methods of spreading the disease. In view of the possibility that occasional ram lambs might become infected whilst suckling their dams, the application of this segregation method together with the serological testing of the lambs at weaning and again at, say, ten months (as planned by Victorian workers) could be expected to eradicate the disease.
The use of the complement fixation test, together with clinical examination, and culling reactors and affected rams can reduce infection rapidly in a flock. If repeated at intervals it can be expected to eliminate infection entirely.
Vaccination as a means of preventing infection in rams, and to a lesser extent in ewes to reduce abortions and neo-natal losses, has been developed by Buddle in New Zealand over the last few years. The high incidence of the disease, and its importance as a cause of ram wastage and abortion in New Zealand, prompted work on the preparation of a vaccine which commenced in 1954.
Intensive laboratory work and field trials over the next few years enabled Buddle to produce an effective product which will confer substantial protection on rams against either natural or artificial infection. This adjuvant vaccine, which is a saline oil emulsion of killed Brucella ovis organisms, is rendered far more effective, however, if used simultaneously with Brucella abortus Strain 19 vaccine; so commonly used for cattle. Final protection figures on extensive feld trials in 1958, involving some hundreds of rams, may be mentioned briefly to demonstrate convincingly the value of this vaccine. No less than 76, or 43 per cent. of 176 rams, became infected from other infected rams when both groups were joined with ewes for an eight week mating period. Only eight rams, or 5.5 per cent. of 146 rams, vaccinated simultaneously with the adjuvant vaccine and Strain 19 became infected when mated with the same groups at the same time.
The optimal time of vaccination is still under consideration, but vaccination as hoggets or at weaning is at present recommended. In young sheep a second vaccination may be necessary.
Strain 19 has produced some temporary changes in the semen picture of rams and consequently the recommendation is not to vaccinate within two months of mating. The duration of immunity would appear to persist for at least two years. Vaccination of ewes has not given results as conclusive as those with rams and trials are being continued. However, early results were encouraging.
Despite the extensive trials and over-all good results in New Zealand, and the fact that over one quarter of a million sheep have been vaccinated in the Dominion, only small numbers of rams have been vaccinated in this state and no controlled trials have yet been reported in Australia; mainly because State Authorities have not recommended this method of control. The reasons why vaccinations have not been officially supported here would appear to be: 1. The disease is generally not as important as in New Zealand. 2. The extensive use and high regard of the value of the Complement Fixation Blood Test by Australian workers and the fact that the disease has been eradicated from flocks by segregation, clinical examination and blood test. 3. Commonwealth authorities insist on a negative blood test for all rams being exported. Vaccination titres, which cannot be distinguished from infection titres, will persist for many months after vaccination. Two of five rams vaccinated when eight months old still had positive titres eleven months after vaccination. Blood tests are required also by some buyers of stud rams. 4. Vaccination is effective in reducing infection but without the use of blood tests would be a very slow or doubtful method of eradicating the disease from a flock. 5. Cost is about 2/6 per dose; and in view of the use of Strain 19. vaccination must be carried out by a registered veterinarian.
REFERENCES
Buddle. M. B. (1954)-N.Z. vet. J., 2: 99
(1957) - ibid. 5: 43
(1958)-ibid. 6: 41
Buddle, M. B. and Boyes B. W. (1953)- Aust. vet. J. 29: 145
Gunn. R. M. C. Sanders, R. N. and Granger, W. (1942)-Bull Coun. sci. industr. Res. Aust. No. 148.
McFarlane, D., Jebson, J. L., Hartley, W. J., Salisbury. R. M. and Osborne. H. G. (1952)- Aust. vet. J. 28: 221.
McGowan, B. and Shultz. G. (1956)-Cornell Ver. 46: 277.
Simmons, G. G. and Hall, W. T. K. (1953)- Aust. vet. J. 29: 33.
Keogh, J., Doolette. J. B. Clapp, KH. (1958) - Aust, vet. J. 34: 412.
Klapp. K. H. (1955) - Aust. vet. J. 31: 27.
Moule, G. R. (1950) - Aust. vet. J. 26: 29
Watts. PR. (1955) - Aust. vet. J. 31: 1.
Doolette. J. B. (quoted by Watts-ibid 31: 1)
Miller. K. S. (quoted by Watts-ibid 31: 1).