PATHOGENICITY OF BR. ABORTUS FOR SMALL ANIMALS 829 



Pathogenicity of Br. abortus for Small Animals. 



In GUINEA-PIGS a disease is set up closely resembling that caused by Br. melitensis. 

 After intramuscular inoculation a local suppurating lesion is rare, but abscess formation 

 in the testis or epididymis is not uncommon. A mild infection can be produced in rabbits, 

 RATS and MICE. The morbid anatomy and histopathology of the disease have been described 

 by Fabyan (1912). In mice inoculated subcutaneously with 10-1000 million organisms a 

 retrogressive disease is set up. The organisms can be demonstrated in the regional lym- 

 phatic glands and the spleen for a month or so, and agglutinins are present in the blood 

 serum. Mice may also be infected by feeding with large doses, rats may be infected 

 by feeding as well as by intraperitoneal inoculation, and the organisms may be excreted 

 for a time in the urine and faeces, but unless very large doses are used the infection retro- 

 gresses (Ber 1936, Sandholm 1938, Bosworth 1938). According to Emmel and Huddle- 

 son (1929, 1930), FOWLS can be infected by feeding or parenteral inoculation. The birds 

 stop laying and develop severe diarrhoea. There is a gradually increasing pallor of the 

 head, comb, and wattles, emaciation, and often paralysis and death. The course of the 

 disease ranges from about 2 to 14 weeks. Post mortem, the main lesions consist of a 

 necrotic enteritis and degenerative changes in the liver and kidneys. The majority of 

 other workers, however, who have studied this question, have found that, on the whole, 

 fowls are resistant to infection except with large doses administered parenterally (McNutt 

 and Purwin 1930, 1932, van Roekel et al. 1932, Beller and Stockmayer 1933). With smaller 

 doses the organisms can rarely be recovered from the tissues. In the absence of direct 

 cultural experiments, a rise in the agglutinin titre cannot be interpreted as necessarily 

 indicative of infection. The conclusions of Emmel and Huddleson require confirmation 

 before being accepted. 



Monkeys may be infected with Br. abortus, but they are less susceptible to it than to 

 infection with Br. melitensis. (References to pathogenicity of Br. abortus for small animals : 

 Schroeder and Cotton 1911, Smith and Fabyan 1912, Emmel and Huddleson 1929, 1930, 

 Morales-Otero 1930, McNutt and Purwin 1930, 1932, Bang 1931, Pagnini 1932, Henry, 

 Traum, and Haring 1932, Henricsson 1932, Helms, Holm, and 0rskov 1932, Rainsford 

 1933, Ber 1933, Olin and Lindstrom 1934, Huddleson 1934, Thomsen 1934, Feldman and 

 Olson 1935, Smger-Brooks 1937, Scorgie 1938). For reproduction of disease in larger 

 animals, see Chapter 75. 



Pathogenicity of Br. suis for Small Animals. 



Experimentally, this organism gives rise in guinea-pigs to a disease closely resembling 

 that caused by Br. melitensis. Local abscess formation is rare, but in infections by the 

 American tyi^e large suppurating lesions, few in number, are not uncommon in the spleen, 

 liver, lymph glands, testicles, and joints. The Danish type appears to be less virulent than 

 the American type. Br. suis appears to resemble Br. abortus in its infectivity for mice, 

 rabbits, and fowls, but there is Httle exact information available. For mice Br. suis 

 is said to be more virulent than Br. abortus (Singer-Brooks 1937). For monkeys it appears 

 to be perhaps even more virulent than Br. Tuelitensis. (References to pathogenicity of 

 Br. stiis for small animals : Smith 1926a, Hardy et al. 1930, Cotton 1932, Thomsen 1934, 

 Huddleson 1934, Feldman and Olson 1935.) For reproduction of disease in larger animals, 

 see Chapter 75. 



Variation. — It has already been mentioned that under artificial conditions of 

 cultivation Brucella strains, particularly of the melitensis type, tend to undergo a 

 change which is characterized by a gradual loss of specific, and gradual increase of 

 non-specific, agglutinability, together with a decrease in virulence to animals. 

 This change appears to be an example of the smooth — >■ rough variation. Whether 

 the change is accompanied by any corresponding alteration in the morphological 

 and colonial appearances of the organisms is still a little doubtful, though there is 

 reason to believe that some change does occur. The descriptions of various workers, 



