Chapter 25.

BRUCELLOSIS/GRAM +VE BACILLARY INFECTIONS

 

25.1 Summary

The genus Brucella consists of small non-motile, non-spore forming bacteria, that grows very poor on ordinary media and may require special supplementation. They are aerobic and do not grow well under strict anaerobic condition, but growth is often improved by CO2. This gas (5-10%) is required for primary isolation. Isolation is facilitated by the addition of blood, liver infusion or other materials to the media.

There is a variety of Brucella that are host adopted. Differentiation of species, therefore, depends on subjecting them to various tests. Some strains of Brucella can grow in the presence of certain dyes such as theonine, pyronine, basic fuschin and methyl violet, others can not. On suitable media hydrogen sulfide is produced by most strains of Br. abortus and by B. suis but not by B. melitensis. Brucella abortus will not grow unless the CO2 concentration of the atmosphere is increased. Brucella melitensis do not have this requirement. Two antigenic groups of Brucella are recognized. One includes Br. abortus and B. suis the other, B. melitensis. 

Brucellosis also known as Bang's disease (or contagious abortion) in cattle is of great economic importance and causes significant loses in the cattle industry. It is also a public health problem and is controlled in the United States by slaughter of infected animals and the practice of calfhood vaccination. The most important species in domestic animals are Br. abortus (bovine), B. melitensis (Caprine), B. suis (swine) and B. canis (dog). 

In man brucellosis is known as malta or indulant fever. The disease in man is characterized by a rather long incubation period, general aches and pain and an irregular (undulating) fever which continues into a chronic stage. Veterinarians should be especially careful because the disease may be contracted through pregnancy testing of infected cattle. The disease can be prevented in most people by the use of pasteurized dairy products, therefore, immunization is not employed nor has it been found to be satisfactory. In cattle an attenuated Br. abortus strain (strain 19) is used to prevent the disease. Brucella canis causes serious abortion in dogs and may be transmitted during breeding or whelping.

 

25.2 Key words:

Abortion,

cross-agglutination,

M-antigen,

molk ring test,

card test,

complement fixation test,

attenuated strain 19,

market ring testing program,

lymphocyte blastogenesis,

bacteremia,

biotype,

antiglobulin test.

 

25.3BRUCELLOSIS 

Brucellosis is a worldwide problem of both public health and economic importance. It is of public health significance not only because of direct consequent illness, physical incapacity, and loss of manpower, but also because it causes a serious diminution of much needed foodstuffs, especially animal protein, which are essential to human health and well being. Since brucellosis is not generally transmitted from person to person, the prevention of human infection depends upon the control and elimination of this disease in animals. The gravity of brucellosis in terms of human illness and economic loss remains a matter of major concern. 

Loss of livestock, and hence animal protein, occurs from abortion, premature birth, and infertility and decreased milk yield. 

The recognized modes of transmission to man are ingestion, contact, inhalation, and accidental inoculation. 

Infection by ingestion may occur via the gastrointestinal tract or by penetration of the mucous membrane of the throat. The usual vehicles of infection for man are: 

Contact with Brucella in vaginal discharges, fetuses, placentas, urine, manure, carcasses and salvaged animals causes a large portion of human cases. The skin and mucous membranes, including the conjunctivae, provide the portals of entry. The contact route of transmission is especially, packinghouse workers, animal handlers, factory workers engaged in the primary processing of wool, and laboratory workers. The chances of infection are particularly high during the season in which abortions occur, mainly because of the actual massive contamination of the premises. 

Infection occurs when man inhales infected dried materials of animal origin, such as the dusts from sheep wool, railway cars and trucks that have transported infected animals, abattoirs, infected farm premises, and Brucella laboratories. Infection by accidental inoculation is not infrequent among veterinarians and laboratory workers.

Brucella are defined as: 

Coccobacilli or short rods, 0.5-0.7 x 0.6-1.5 u, arranged singly, more rarely in short chains. No capsules. Nonmotile. Do not form endospores. Gram negative. Do not show bipolar staining. Chemorganotrophs. Metabolism by respiration.

Require the following vitamins for growth:

thiamine, niacin, biotin. Calcium pantothenate often stimulates growth. 

Haemin (X factor) and Coenzyme 1 (V factor) are not required. 

Catalase positive; oxidase is usually positive, but Br. neotomae and Br. ovis are oxidase negative. Urea hydrolyzed to a variable extent. Nitrates reduced to nitrites (except Br. ovis). Citrate not utilized. Indole not produced. Methyl red test and Voges-Proskauer reaction negative. Litmus milk-no change. 

Strict aerobes.

Some require 5-10% added CO2 for growth, especially on initial isolation. 

Temperature range:

20-400C, optimum 370C. Optimal pH 6.6-7.4. 

Mammalian parasites and pathogens. Facultatively intracellular with a relatively wide host range. 

The guanine plus cytosine content of the DNA ranges from 56-58 moles percent (buoyant density). Members of the genus comprise a closely knit and sharply demarcated genetic group as defined by DNA hybridization studies. 

25.4 BRUCELLA SPECIES 

25..4.1 Brucella melitensis 

Aerobic. Produces no H2S, or not more than a trace, on peptone media. Usually grows in the presence of basic fuchsin and thioneine. Usually M antigen predominant. Usually pathogenic for goats and sheep, but can also affect other species including cattle and man. Three biotypes are recognized. 

25.4.2 Brucella abortus 

Usually requires added CO2 (5%) for growth, especially upon primary isolation. Usually produces moderate amounts of H2S but may be negative. Usually growth in the presence of basic fuchsin, but inhibited by thioneine, usually has an antigen predominant. Cultures in the smooth or smooth-intermediate phase are lysed by brucella phage Tb at routine test dilution. Usually pathogenic for cattle causing abortion, but can also affect other species including man. Nine biotypes are recognized.

25.4.3  Brucella suis 

Produces large amounts of H2S or none at all. Grows in the presence of thioneine, but usually inhibited by basic fuchsin. Usually has A antigen predominant. Usually pathogenic for pigs, but can also affect hares and other species including man. Four biotypes are recognized. 

25.4.4 Brucella ovis 

Requires added CO2 for growth. H2S not produced. Grows on basic fuchsin and thioneine. Even on primary isolation, cultures are in the non-smooth phase and do not possess the A and M antigens of smooth Brucella. Not lysed by brucella phage Tb. Pathogenic for sheep--causes epididymitis in rams and may cause abortion in ewes. Cross-agglutinates with Br. canis and with other species (rough variants only). Although Br. ovis polynucleotides are similar to those of other Brucella spp., Br. ovis lacks some of the polynucleotide sequences present in Br. suis DNA and appears to be a deletion mutant. 

25.4.5 Brucella canis 

Aerobic. Does not produce H2S. No growth on basic fuchsin, but does grow on thioneine. Even on primary isolation, cultures are in the non-smooth phase and do not possess the A and M antigens. Not lysed by brucella phage Tb. Cross-agglutinates with Br. ovis and rough variants of other Brucella spp. Pathogenic for dogs, causing epididymitis and abortion. 

25.5 BOVINE BRUCELLOSIS 

25.5.1 Diagnostic Methods 

25.5.1.1 Serological Herd Screening Tests 

25.1.1.1 Milk Ring Test for dairy herds:

The milk ring test is the most practical method for locating infected dairy herds and for surveillance of brucellosis-free herds. It is performed on samples obtained from milk that is in cans or in bulk, and if repeated at least three times a year on each herd will detect the vast majority of infected herds. In eradication programs, herds that show a positive ring test should be examined by serological tests to identify the infected animals. 

Continual surveillance of brucellosis-free herds is a simple procedure with the milk ring test. Samples collected for routine determination of butterfat can be tested periodically by the milk ring test. The original procedure has be modified to maintain uniform sensitivity of the test under various conditions, i.e., for the examination of samples of cream, preserved milk, milk from bulk tanks, and milk from very large dairy herds. 

Vaccination of adult animals with Br. abortus vaccine strain 19 can produce positive reactions to the milk ring test. False positive or suspicious reactions may be obtained during the drying-off period if colostrum is present in the sample or if mastitis is present in the herd. 

25.1.1.2 Market Cattle Testing Program for Beef Herds:

In many areas it may not be practical or economically feasible to perform blood tests on entire beef herds. Market cattle testing programs can provide a method of screening and of continual surveillance with a minimum of effort. Animals sent to slaughter are identified, by means of a back tag or other suitable marker. with the owner and farm of origin. The responsibility for identification rests with the first person receiving control of the animal as it moves from the farm to the abattoir. Blood samples are collected at the abattoir and are sent to an official laboratory for testing.

 

25.5.1.2 Serological Tests for Individual Animals 

25.5.1.2.2 Serum Agglutination Test:

Although the serum agglutination test remains the most commonly used diagnostic test for bovine brucellosis, its limitations are recognized. Not all infected cattle show a diagnostically significant titer, which may be negative during the incubation stage. In animals exposed for the first time during pregnancy, it is not unusual for agglutinins to appear only several days to two weeks after abortion or parturition. Also, during the later stages of pregnancy, a small proportion of animals show a transitory reduction in titer associated with the physiological movement of immunoglobulins from the circulation to the mammary gland. The tests may be negative in chronic infections also. 

Following vaccination with Strain 19, agglutinins may persist longer than antibodies detected with other tests. Heterospecific agglutinins, due to cross reactions with other organisms, may interfere in some cases. 

25.5.1.2.2 Tube Agglutination Test:

Because of the wide variation in methods employed in various countries, the Joint FAO/WHO Expert Committee on Brucellosis recommends that the sensitivity of the agglutination test, and the diagnostic criteria in a given country, be stated in terms of the International Standard for Anti-Brucella abortus Serum (ISAbS), which has been assigned a unitage of 1000 IU/ml. The Committee recommends that the minimum diagnostic level by 100 IU/ml for non-vaccinated animals or those of unknown status, and 2000 IU/ml for vaccination animals. Levels 50% lower than these, i.e., 50 IU/ml for non-vaccinated animals and 100 IU/ml for vaccinated animals, should be regarded as "doubtful" or "suspect". 

Animals that are doubtful or suspect should be retested in 60 days. If, however, the animals are in herds that are otherwise free of infection, supplemental tests can be used to determine their infection status without waiting for retesting. 

If prozones are a problem, this can be minimized by suspending the antigen in a 5% solution of NaCl. 

25.5.1.2.3 Rapid Plate Agglutination Test:

Until recently, the rapid plate agglutination test was the only test employed in many areas of the USA and Canada. Mass testing with this fast, simple test, slaughter of animals giving a positive reaction, and vaccination with Strain 19 reduced the incidence of bovine brucellosis to such a level that it was technically feasible to use more complicated tests to detect the remaining infection. 

The test is less sensitive than the tube agglutination test but is less affected by the prozone phenomenon. It may be used as a screening test in areas of low incidence, or for recertification of brucellosis-free herds. Any reactors to the plate test in such herds should be retested by the tube agglutination test and by the complement fixation test or supplementary tests. 

25.5.1.3 Other Tests for Brucellosis 

25.5.1.3.1 The Rose Bengal Test.

The Rose Bengal plate test is a rapid slide agglutination test in which the antigen consists of Br. abortus stained with Rose Bengal. The test is rapid and cheap. It provides results comparable to the tube-agglutination and complement-fixation tests, and it gives negative reactions sooner in vaccinated calves, an advantage in distinguishing vaccinated from infected animals. 

25.5.1.3.2 The Card Test.

In 1967, Nicoletti recommended the use of the card test as a rapid, sensitive, and accurate means of screening for brucellosis, especially inrange areas. The antigen is a stained, buffered whole-cell suspension of Br. abortus strain 1119-3. The antibody source is plasma produced by the use of an anticoagulant and lectins, which produce rapid clumping of erythrocytes and allow rapid extraction of plasma. Only one antigen-plasma or serum dilution is made, and the results are read as positive or negative on this basis. 

25.5.1.3.3 The complement-fixation test.

The technique of this test varies in different laboratories; in recent years it has been adapted to the microtiter system, requiring small quantities of reactants and allowing the test to be particularly valuable in detecting chronically infected animals that no longer give a positive reaction in the agglutination test.

An antiglobulin test for the diagnosis of chronic cases of human brucellosis was developed. The test found that specific antibodies of the classes IgG and IgA will not cause agglutination of Br. abortus cells, but will attach to them; subsequent agglutination can be developed using anti-immunoglobulin serum. A similar antiglobulin test was developed to investigate serological responses to Strain 19 and 45/20 vaccines was found to be a potentially useful test for differentiating vaccinated from infected cattle. 

Various forms of radioimmunoassay tests and different methods of performing lymphocyte blastogenesis tests on Brucella antigens are presently being investigated. Both systems show promise but must be subjected to the rigors of extensive use in the field before their precise value is known. (Ref. Hagan and Brunner) 

25.5.1.3.4 Cultural Examination:

Isolation of the organism is the definitive method of diagnosis. The use of selective media containing antibiotics has increased the likelihood of isolation of Brucella from vaginal discharges, placentae, aborted fetuses, and milk. Milk samples with a high ring test titer are most likely to contain organisms. In choosing a medium for isolation from bovine materials, it must be remembered that many field strains are serum=dependent and/or dye-sensitive. 

Finally, it is emphasized that a negative result in any diagnostic test or combination of tests for a single animal does not preclude the possibility of infection. Brucellosis is a herd disease, and the status of the herd must be considered when interpreting a single test. It is recommended that tests be repeated at appropriate intervals of time, and preferably that more than one type of test be applied in order to resolve this uncertainty. 

25.5.1.4 Vaccination 

25.5.1.4.1 Vaccination with Strain 19 

The living attenuated vaccine, Br. abortus Strain 19, remains preeminent among the vaccines used in the control of bovine brucellosis. This strain has a stable, low pathogenicity and a relatively high immunogenicity, and does not spread from animal to animal. These characteristics are maintained by the careful selection of seed cultures, the preparation of an original seed with the desired properties for vaccine production, and preservation in the freeze-dried form. The resistance-inducing properties of Strain 19 vaccine are directly dependent on the colony type and the viability of constituent cells. Proper governmental control is extremely important to insure the production of vaccines with desirable qualities. The protection induced by Strain 19 vaccination is relative. 

Heifer calves, vaccinated with Strain 19 at 3-4 months of age and challenged during their first pregnancy, were shown to possess an immunity equal to that produced in heifer calves vaccinated at 6-8 months of age. Vaccination at the younger age has the advantage of eliminating persistent vaccinal titers, which cause difficulties in the interpretation of serologic tests. The protection afforded by Strain 19 vaccination of adult cattle is comparable to that of calves vaccinated at 6-8 months of age. However, because of the recognized disadvantages of vaccinating mature cattle, this practice is not recommended. Persistent blood agglutinin reactions are usually observed in vaccinated adult animals, and an occasional abortion may be caused by vaccination of pregnant animals. There is insufficient evidence to indicate whether the vaccinal resistance of cattle of comparable ages is influenced by pregnancy. 

Controlled studies in female cattle have not provided evidence that vaccination causes temporary or permanent infertility. Vaccination of infected animals has no effect on the course of the disease. 

Vaccination of bulls with Strain 19 is NOT recommended. Serum agglutination titers resulting from vaccination tend to persist longer in bulls than in cows. Moreover, Br. abortus indistinguishable from Strain 19 has been isolated from the genital tract of several vaccinated bulls. Reports suggest that orchitis and lowered fertility may result from vaccination. 

Brucella abortus Strain 19 has also been isolated from the milk of a few lactating cows that were vaccinated as heifer calves and maintained under field conditions. Most of these cattles had infection in one quarter of the udder. Estimates of the frequency of Strain 19 infection of the udder vary from 1.8 to 5.6 per 100,000 vaccinated animals, most of which were 8 months of age or older at the time of vaccination. As significant as age at the majority of the Strain 19-infected animals were early maturing dairy breeds (Jersey and Guernsey), some of which were vaccinated at 6-8 months of age. Usually only one Strain 19-infected animal was found in a herd. 

25.5.1.4.2 Duration of Protection 

In controlled experiments, animals vaccinated subcutaneously as calves (at 6-8 months of age) with a single dose (60 x 109 to 80 x 109 viable cells) of Strain 19 are usually resistant to infection with virulent Br. abortus for seven years and probably longer. Revaccination with Strain 19 does not significantly improve the original vaccinal immunity. The prolonged protection in animals vaccinated as calves is due to the immunogenicity of the vaccine and the response of the host, and not to an increase in age of the animals. 

25.5.1.4.3 Routes and Site of Vaccination and Dosage 

Reduced dosage by the intradermal, intracaudal, or subcutaneous route appears to give sufficient protection for the subsequent pregnancy. This method has, however, mainly been used in animals vaccinated at the age of 12-18 months or more. Similar information on animals vaccinated by the intradermal and intracaudal routes at the age of 6-8 months is very limited. The optimal does of Strain 19 vaccine for each method of administration is not known. The dose recommended below provides a safety margin that ensures injection of the recommended number of viable cells. 

The subcutaneous inoculation of the vaccine is best made at a site where it is naturally distributed by the movements of the animal, i.e., the upper third of the lateral surface of the shoulder or immediately posterior to the shoulder. 

25.5.1.4.4 Dried Vaccines

 The principal advantage of a dried product is that it can be stored at 4-70C for at least a year without important loss of viability. The viability of freeze-dried vaccine decreases rapidly at 270C and more rapidly at 370C. When the vaccine is transported over long distances in hot climates, it should be transported under refrigeration. Reconstituted vaccine should be used immediately. The number of dead cells in the vaccine should be kept as low as is practical, because of the toxicity of killed as well as live Brucella cells. 

25.5.1.5 Control and Eradication 

Effective information campaigns are a necessary part of control and eradication programs. The support of livestock owners can be assured only when they are fully aware of the benefits to be derived from establishing brucellosis-free herds. Factual data relating to the nature of the disease, the incidence of infection, and the resultant economic loss may be used to an advantage in this respect. Unless it is understood in the cattle industry that it is not economical to live with brucellosis, there is a danger that complacency may impede progress from control to eradication. 

Efficiency and economy in controlling and eradicating brucellosis can be accomplished by utilizing surveillance procedures to detect infected herds. The milk ring test is especially valuable for locating infected dairy herds with a minimum of effort and expense, thereby eliminating the need for extensive blood testing in herds that are free from brucellosis. Moreover, this procedure permits the frequent testing necessary to identify foci of infection before they can cause dangerous extensions of the disease. 

For herds or areas where the milk ring test is not practical, such as in beef herds, the testing of blood samples collected from animals moving in trade through auction markets, stockyards and abattoirs, also called market cattle testing, is of great value in locating foci of infection. 

The advantages of vaccination programs continue to be confirmed in herds and areas where approved vaccines are properly applied. Such a program can be used effectively in areas of heavy infection, to reduce incidence rates to a point where procedures based on testing and the elimination of reactors are possible without serious economic loss to owners of infected herds. 

As eradication campaigns advance and the incidence of brucellosis in cattle is reduced in a given area, it becomes necessary to consider elimination of other sources of brucella infection. In view of the recognized inter-species transmission of different brucellae, control and eradication of the disease cannot be limited to a single susceptible host. At the same time, it is equally important to limit the extension of bovine brucellosis that may occur through normal movements of cattle. This can best be accomplished through the application of appropriate regulations or laws governing cattle movements both within and between countries. For example, cattle introduced into brucella-free herds, areas, or countries must be from brucella-free herds, areas, or countries. It has been shown that, unless such precautions are taken, progress in controlling or eradicating the disease may be seriously delayed. 

The following type of program is recommended for the eradication of brucellosis: 

1. Surveillance procedures for detecting infected herds: 

2. Control procedures for detecting potentially infected herds:

25.6 PORCINE BRUCELLOSIS 

25.6.1 Brucella Suis

Brucella suis(biotypes 1, 2 and 3) causes an economically important disease in swine. The available evidence indicates that the pathogenesis of the disease caused by each biotype is very similar. 

On the otherhand, the general epizootiology of type 2 is different from that of types 1 and 3. New outbreaks of type 1 and 3 infection in swine are usually the result of contact with infected swine, whereas outbreaks of type 2 infection in swine are frequently the result of contact with infected European hares or their carcasses. Brucella abortus infection may occur in swine, but it is not economically important and apparently is not transmitted to other animals. 

The disease usually runs an acute course when first introduced into a herd of swine. In some herds, particularly small ones, the disease may disappear or cease to be an important problem because some infected animals recover and most are removed for slaughter in the course of normal farming practice. In larger breeding herds, the infection usually persists as a chronic disease in adult swine, and appears again as an acute condition in the next generation. 

25.6.2 Diagnosis 

The diagnosis of swine brucellosis is usually based on serum agglutination tests. Complement fixation, antiglobulin (Coomb's), and allergic tests are also used in some countries. The use of modified serum agglutination tests has become more common recently. An agglutination test that utilizes buffered Brucella antigen is being used with increasing frequency in the USA. 

All the serological tests are effective in detecting the presence of individual animals. There are some swine from which Brucella may be isolated that do not react in serological tests. It thus becomes necessary to use these tests as herd diagnostic procedures and to base any attempts at control on entire herds or units, rather than on individual swine. Caution should be exercised in the purchase of individual swine with a negative or low titer antibody response, unless the status of the entire herd of origin is known. 

Judgment must be used in the interpretation of standard agglutination tests since, in nearly any sizable herd of swine, low titer reactions occur in the absence of infection. These same low titer reactions occur in herds where infection is present. As a practical rule, agglutination reactions at the 50 IU/ml level or less are considered negative, unless there are definite reactors in the herd at the 100 IU/ml level or higher. The problem of low titer reactions in noninfected swine is considerably decreased by use of the buffered Brucella antigen test or other modified agglutination tests (heat inactivation at 560C, acidified plate antigens, rivanol, and 2-mercaptoethanol). However, modified agglutination tests usually do not detect as many infected swine as do the standard serum agglutination tests, particularly during the early stages of infection. 

25.6.3 Vaccination 

Strain 19 vaccine does not protect swine against Br. suis infection. A living vaccine prepared from a Br. suis strain of reduced virulence was shown to produce some immunity for 9 months, but not for 24 months. 

Encouraging clinical results have been obtained in field trails using a vaccine composed of an attenuated strain of Br. abortus and lipopolysaccharide antigen made from heat-killed Br. suis. Also, a vaccine prepared from endotoxin-containing extracts of Br. suis has been shown to produce some immunity in weaning pigs that were exposed to virulent Br. suis 6 weeks after vaccination.  

25.6.4 Control and Eradication 

Control and eradication programs for porcine brucellosis are not supported by as much experience as are those for bovine brucellosis. Control schemes based on officially recommended rules and regulations are being tried on an area basis in the USA. The progress being made is evidence that eradication of swine brucellosis from a large area is both possible and practical. 

Possibly the greatest step that has been made towards the control and eradication of swine brucellosis in the USA is the testing of discarded breeding stock at abattoirs (Market Swine Testing) in order to detect infected herds. A major difficulty associated with this procedure continues to be the lack of a reliable system of identifying swine, so that reactors can be traced back to their herd of origin. Testing of swine at the time of slaughter is most applicable to commercial herds, because a relatively high percentage of the breeding stock is replaced annually. Testing of breeding stock in purebred herds is usually done on the farms. 

The large number of swine in a herd, their prolificacy, and the use of community boars, the widespread use of the sale barn, and breeding for more than one litter per year all affect the control of the disease. 

25.6.5 Prevention 

The most important preventative measure is prohibiting the introduction of infected swine into a brucellosis-free herd. This is best accomplished by purchasing replacements or additions from herds known to be free from brucellosis. If this is not possible, each addition should be tested, and no animal with any degree of agglutination reaction should be accepted. Replacements from herds of unknown history should be kept in isolation for at least 60 days, and retested before entry into clean herds is permitted. The practice of assembling a herd of swine from many different sources is dangerous. It is safer to purchase animals from one source, thus lessening the changes of purchasing an infected hog which does not react to the agglutination test. Herd sires should be purchased well in advance of breeding time, so that a minimum of two blood tests, at least 60 days apart, can be made before service.

 The use of community boars is a hazard to brucellosis control. The practice of lending boars to neighboring herds should be prohibited because of the danger of infection being spread in either direction. 

Swine may spread or contract brucellosis while being exhibited at fairs and shows. Such swine should be held in isolation upon their return, and be shown to have a negative test before reentering the main herd. 

25.7 BRUCELLOSIS IN DOGS 

It has long been recognized that the dog can act as a mechanical and biological vector of Br. abortus, Br. suis, and Br. melitensis. In nearly all cases the source of the canine infection can be traced to the consumption of materials from infected domestic and wild animals, or to contact with them. Wild carnivora, such as foxes and wolves, have also been shown to be infected with these Brucella species. 

In contrast to the sporadic occurrence of brucellosis caused by Br. abortus, Br. suis, or Br. melitensis in dogs kept as pets or as working dogs, or in wild carnivora, a highly contagious form caused by a new species, Br. canis, was observed in kennels of beagles in the USA. Although the disease is known primarily in beagles, other breeds may be infected. It appears to be widespread in the USA in commercial breeding establishments that do not maintain closed kennels. 

Brucella canis grows well, without added CO2, on the media used for the isolation of other Brucella species. It will grow on antibiotic selective media, provided that these do not include dyes. on primary isolation, Br. canis is in the non-smooth form. 

The disease caused by this organism is characterized by abortion at 40-50 days gestation, early undetected embryonic death, prolonged vaginal discharge following abortion, enlargement of lymph nodes, splenitis, and prolonged bacteremia. Males may appear normal, or there may be epididymitis, prostatitis, testicular atrophy, loss of vigor, and lassitude as well as lymphatic involvement and bacteremia. Spontaneous recovery may occur, but the disease is very prolonged and may lead to infertility in both sexes. 

The organism can be isolated from the blood of males or females, the vaginal mucus and the milk of bitches that have recently aborted, the placenta, the fetal liver and lung, and the urine of male dogs. 

Spread of infection occurs at the time of breeding or whelping. 

The disease resembles that caused by other Brucella in that if affects primarily the reticuloendothelial and reproductive systems. The persistent bacteremia in both experimental and natural infection, in the absence of fever, is an unusual feature of this disease. 

Antibody can be detected by the agglutination test using Br. canis antigen. Antibody titers are high throughout the bacteremia period; although they decline when the blood cultures become negative, they may persist for some time. 

Successful vaccines have not yet been developed and chemotherapy has not been effective. The disease can be eradicated from a colony of dogs by monthly bacteriological and serological examinations of blood and the removal of reactors. 

At least four laboratory workers have been accidentally infected with this organism. 

Cattle, sheep and swine were exposed to Br. canis by the conjunctival route and appeared to have a low susceptibility. There was no evidence of localization in genital tracts or of animal-to-animal transmission.

 25.8 BRUCELLOSIS IN HORSES 

Brucella abortus (biotype 1) has been recovered from the aborted fetuses of mares and donkeys, as well as from cases of distulous withers and bursitis. Other clinical symptoms include arthritis, chronic intermittent lameness, and more rarely an acute form characterized by pyrexia and prostration. 

Man can be infected from horses, but transmission is probably by contact rather than by the ingestion of koumis (mare's milk), the acidity of which kills Brucella organisms. The horse is usually infected by contact with infected cattle, but may be relatively resistant to Brucella infection. There is no information on the transmission of brucellosis among horses.

 25.9 Further reading on Brucellosis: 

Joint FAO/WHO Expert Committee on Brucellosis. Fifth Report. Geneva, June 29-July 6, 1970. Published by FAO and WHO, Food and Agriculture Organization of the United Nations, Rome, 1971. 

Review Lecture 26-28 page 15, Questions 9-13. 

Study Questions: 

1. Explain how brucellosis cause losses to the animal industry.

2. How is brucellosis transmitted?

3. Describe the nutritional, biochemical requirement for growth of Brucella abortus.

4. Describe the following serologic test for brucellosis:

Milk ring testing

Rapid plate agglutination test

Compliment fixation test

Card test

Rose bengal plate test

5. What are false positive and false negative reactions and how do they come about?

6. How are brucellosis in swine identified at slaughter market?

7. Brucella organisms are known to grow and multiply within the host cell. What other organisms are related to Brucella in this respect? What host cells are involved?

8. Intracellularly, these organisms mediate what kind of immunity?

9. What are the vitamins requirement for the growth of Brucella? Why do we not use it in our laboratory exercises?

10. Discuss the brucellosis control and evaluation program in cattle. Why is it difficult to maintain such a program in swine? What is the public health significance of brucellosis?

11. Describe brucellosis in dog. 

References: 

Hagen: Infectious Diseases of Domestic Animals

Gibbous, Catcolt and Smithcors: Bovine Medicine and Surgery and Herd Health Management

Davis, et al: Microbiology