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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
NOTES ON RECENT RESEARCH WORK WITH BRUCELLA SUIS INFECTION
R. O. C. King. B.V.Sc., R. M. Kinross Research Officer, Veterinary Research Station, Glenfield.
It has been shown by workers in other countries that spread of Brucella infection in pigs is commonly caused by the infected boar. This has been substantiated in New South Wales and the ease with which Br. suis has been isolated from the boar semen indicates the danger of keeping an infected boar in a herd. The infected boar is not always a spreader of the disease, however, as is shown by a case encountered in New South Wales where the only boar in the herd was the only reactor found on test of the whole herd. This sire had been mated with all the 32 sows at least once and with most of them three times. He was quite potent and ran with the sows. When this animal was destroyed his genitalia and bladder were forwarded to the Research Station where Br. suis was isolated by guinea pig inoculation from the right seminal vesicle and urine.
Infected Boars.
Twelve positively reacting boars have been examined to date. These were obtained from a total of 19 boars tested so that in this small series of animals, all taken from infected farms, 63% of boars reacted to the agglutination test. With two exceptions all infected farms encountered to date have had at least one boar infected so that where the agglutination test is being used to establish a diagnosis of Brucellosis, or in survey work, it is important to obtain serum samples from all boars on the farm.
Experience in the field and at Glenfield has shown that comparatively few boars infected with Brucella suis show clinical symptoms of disease. Of the twelve positive reactors mentioned above only two showed lesions, and these were encountered on the one farm. Both showed clinical symptoms; in one case both testes were involved, one being slightly enlarged and considerably fibrosed while its fellow was smaller than normal and appeared soft, on palpation. In the other case one testis only was involved, it being smaller than normal and very fibrosed. The absence of symptoms in the boar is therefore no indication of freedom from disease.
All of six reacting boars examined post-mortem were proved to be infected with Br. suis. A positive agglutination test is therefore evidence of actual infection in the boar. Semen from four infected boars has been examined on ten occasions and Br. suis has been isolated on nine. Of the four boars three were potent, including an animal with an obvious lesion in one testis. The fourth boar was the animal noted above as showing obvious lesions in both testes. He was impotent; his semen showing aspermia on each of three examinations, but Br. suis was isolated at each examination. This supports the opinion that the infected boar commonly excretes Br. suis in his semen.
Two infected boars have been observed to show inability to erect the penis while exhibiting apparently normal sexual desire. One animal was a naturally occurring case, the other having been experimentally infected. In each case the animals had shown normal sexual function previously and had impregnated sows. They apparently lost the ability to erect their penis quite suddenly and would display normal sexual desire by performing the actions of copulation although the penis was not observed to enter the sow's vagina. One of these animals was kept under observation for two months and at six attempts at mating during this period he showed either inability to erect his penis or complete lack of sexual desire. The other animal was destroyed for post-mortem examination shortly alter he first exhibited sexual disability. Neither animal showed macroscopic lesions in the genital organs on post-mortem examination. It is not certain, of course, that this condition was a result of Brucella infection, but it is recorded as of possible importance and reports of similar observations would be of interest, especially if correlated with agglutination test results.
Cases of death probably due to Brucella infection have been reported from the U.S.A. A single case of this type has been encountered at the Research Station, Glenfield. This animal, a boar, was the naturally occurring case mentioned previously as having one testis obviously diseased. He was held under observation and examination for a period of sixteen months and during this time remained uniformly in good health, there being no apparent alteration in the condition of the affected testis. Overnight he developed an almost complete paralysis of both hind limbs; being found down and unable to rise when an attendant entered his sty to feed him one morning. All attempts to make the animal rise were unsuccessful and he evinced considerable pain during attempts to rise. No change was noted in his condition during the next 48 hours and he was then destroyed. On post-mortem examination it was found that both kidneys, regional lymph glands and bladder were the site of an acute inflammatory process, the kidneys containing large numbers of miliary abscesses. Br. suis was isolated in purity from all sites.
Positively Reacting Immature Pigs.
In field work on the eradication of Brucella suis infection it has been found that while the majority of positive reactors are found in the adult breeding stock, there is usually a number of reactors among the young stock and positive reactors may be encountered in pigs of all ages.
It is known that in Brucella infection of cattle, calves will react to the agglutination test while drinking infected milk but will cease to react at varying periods after weaning. Further, it is known that calves may harbour Br. abortus in the lymph glands of the neck for up to six weeks after weaning from infected milk but that thereafter the organism apparently disappears from their bodies. It therefore was thought advisable to determine whether immature pigs were actively infected and whether they were capable of carrying infection for any length of time.
Firstly, a naturally infected young pig was examined. This animal was the only positive reactor found on test of 47 young stock on a farm where 45 per cent. of 76 adult breeding stock were reactors. On post-mortem examination of this animal no naked eye lesions were found, but Br. suis was isolated from the liver, spleen, lung and ten of the eleven groups of lymph glands examined from all parts of the body.
Following this, sixteen weaner pigs were exposed to experimental infection when four months of age, some via the eye and some orally. These animals comprised two boars, six barrows and eight sows and all except two of them reacted to the agglutination test following exposure. It was planned to kill these animals when from ten months to one year old but for several reasons this could not be done. When it was possible to commence post-mortem examinations only three of the original sixteen animals were still reacting positively to test. Seven of the animals had declined to negative and had been sold for slaughter, while three were reacting within the "suspicious" range. The three positive reactors comprised one boar, one sow and one barrow.
The sow was destroyed one year and two months after exposure. i.e., when one and one half years old. She had not been mated. Examination of her body did not reveal any lesions of disease and guinea-pig inoculations failed to demonstrate Br. suis. However, only half the usual number of guinea-pigs were used in this examination and it is not considered conclusive.
The boar and barrow were destroyed two years and three months after exposure. i.e., when they were two and one half years old. No lesions of disease were encountered but Br. suis was isolated from several sites in their bodies. This demonstrated conclusively that Brucella suis infection may be carried through from immaturity to maturity in the bodies of pigs.
Thus Brucella infection of swine cannot be considered a "self-limiting" disease as has been stated by some overseas authors.
Low-titre Reactions to the Agglutination Test.
Several foreign authors have reported that Br. suis had been recovered from pigs which gave very low-titre reactions to the agglutination test, i.e., reactions not above 1:50. It was considered by them that a pig which gives any reaction at all to the agglutination test should be considered infected.
When agglutination testing of pigs became general in New South Wales considerable thought was given to the interpretation of reactions and at first a conservative attitude was adopted and the results of experience were awaited. Experience has been that low-titre "suspicious" reactions occurred in very much the same way as with cattle. There are three main types of reactor:—
1. Those which give one or more "suspicious" reactions and subsequently give "positive" reactions. These animals are probably infected when the first suspicious reaction is given.
2. Those which give one or more suspicious reactions and subsequently negative reactions. These animals are possibly not infected but always must be treated with caution.
3. Those which give persistent suspicious reactions. Research work has shown that at least some of these animals are actually infected and animals giving this type of reaction must be considered as infected.
In view of the results of recent work at Glenfield and that reported by foreign authors it is probable that a revision of our interpretation of the agglutination titres of pigs is necessary.
At times animals giving reactions as detailed in 2 and 3 above have been encountered in otherwise negative herds and interpretation of such reactions is difficult. In the light of present knowledge it seems very risky to permit a pig showing any agglutination reaction whatever to remain a member of a herd where eradication is in progress.
A very interesting case has been observed recently at Glenfield. A boar, exposed to Br. suis when four months of age reacted in the positive range for approximately three months and subsequently for one year and seven months gave reactions which were never higher than 1:25 and commonly were negative in this dilution. He was exposed a second time and subsequently reacted regularly in 1:25 but never in a higher dilution. Ordinarily this reaction would be considered "negative." He was mated with two persistent suspicious reactors seven or eight months following his second exposure, but these possible further exposures to infection did not affect his titre. It became necessary to subject him to a poet-mortem examination some six months following the last mating and when this was done no lesions of disease were noted but Br. suis was isolated from his genitalia (Cowper's glands).
This animal, therefore, was infected while reacting only in the titre of 1:25, and it is obviously impossible to say whether the organisms isolated at post-mortem had been retained since his exposure at four months or from his subsequent definite or possible exposures.
The important thing is that once any animal has reacted positively to the agglutination test it must be considered potentially dangerous thereafter. It is impossible, of course, in the present state of our knowledge to say whether the phenomenon observed in the case of the above boar is one usually occurring with animals which are exposed to infection and subsequently react in low titre only, or whether he is an unusual case. It is hoped to gain further information on this point by slaughter of animals at present held at the Veterinary Research Station.
Brucellosis of Swine and Public Health.
It is desired to take this opportunity to impress on Inspectors of Stock that Br. suis is an organism which infects man quite readily and may produce serious illness. It is recognised in other countries as the cause of occupational disease in swine-slaughtermen and veterinarians, so that it is desirable to bear this in mind when handling animals which may be infected. When bleeding pigs the use of rubber gloves is not advocated because the life of gloves has been found to be short when handling pigs. The next best thing appears to be to keep a supply of reliable disinfectant accessible in which the hands may be cleaned immediately after blood has come in contact with the skin. When conducting post-mortem examinations it is advisable always to wear rubber gloves.
It is known, of course, that Br. suis may infect dairy cattle under some circumstances. To give an indication of the serious consequences which may ensue when this occurs it may be pertinent to quote an abstract which appeared in the Journal of Dairy Science, 1945, 26; 9. A162. This report showed that in a town whose population was 1,200 some 77 cases of human Brucellosis had occurred. In tracing the origin of the cases it was found that in one dairy which supplied 40% of the milk supply of that town three cows reacted to the serological test. Brucella suis was isolated from the cows' milk and from the blood of affected humans. Pigs had access to the cow yard and it was found that most of the pigs were affected. Brucella suis can be a serious menace to human health and its spread throughout food animals should be checked if possible.