828 BRUCELLA 



that a suspension of Br. abortus has a powerful stimulating effect on the uterine 

 muscle of the virgin guinea-pig. According to Jadassohn, Kiedmiiller, and Schaaf 

 (1934), the Schultz-Dale technique may be used to differentiate between the different 

 types of Brucella, the reaction in sensitized guinea-pigs being type specific. 



Little work has been done on monkeys, but the observations of Huddleson and 

 Hallman (1929), Weigmann (1931), and Zeller, Beller, and Stockmayer (1934) 

 suggest that melitensis and American suis strains are more virulent than abortus 

 strains. (For reproduction of disease in the larger animals see Chapter 75.) 



No exotoxin is formed, but the intraperitoneal inoculation of mice with very 

 large numbers of virulent Br. abortus brings about death within a few days. The 

 toxicity of the organisms is said to be destroyed by heating to 56° C. for 20 minutes, 

 and to be related to the virulence of the strain (Priestley and McEwen 1938). 



Pathogenicity of Br. melitensis for Small Animals. 



Guinea-pigs. — Though death within a few days may follow intracerebral inoculation 

 (Durham 1898, Eyre 1905), or intraperitoneal inoculation with large doses, the disease 

 set up by intramuscular or cutaneous inoculation is chronic, retrogressive, and rarely 

 proves fatal. SmaU numbers of organisms cannot be relied on to cause infection. Most 

 of the animals continue to gain weight. If they are kiUed 6 weeks after inoculation, the 

 following lesions may be found. Occasionally there is a local abscess containing creamy 

 pus. The regional and the more distal lymphatio glands often show a certain amount of 

 hyperplasia of the pale bloodless variety. The spleen may show a variable degree of 

 enlargement, and may contain a number of circular, greyish-yellow necrotic foci, 0-1-0-5 

 mm. in diameter, rarely projecting above the surface. Similar foci, usually few in number, 

 may be present in the liver. Sometimes abscesses are found in connection with the joints 

 or bones. The organisms can be cultivated most readily from the glands, spleen, and bone- 

 marrow. The blood usually contains agglutinins in fairly high titre. The lesions are very 

 variable, and may not be detectable by naked-eye examination. The diagnosis must 

 always be made by testing the blood serum for agglutinins and by cultivation of the 

 causative organism from the tissues. A titre of 1/25 or over is strongly suggestive of 

 infection. The intradermal test with a nucleo-protein extract may be used during life for 

 diagnostic purposes, but reliance must never be placed on it alone. After 6 weeks the 

 diagnosis becomes less easy, because the infection tends to retrogress. Guinea-pigs may 

 also be infected by feeding, by conjunctival or nasal instillation, and by inoculation of 

 the scarified skin. Sometimes they contract the disease natiu-ally from their feUows. 

 (For a description of the histopathology of the disease, see Fabyan 1912.) 



Rabbits appear to be rather less susceptible, but otherwise the infection runs much 

 the same course as in guinea-pigs. The lymphatic system is less affected, and the organisms 

 can rarely be demonstrated in the blood stream. Agglutinin formation is common, but 

 the intradermal reaction is negative. 



Rats and Mice. — There is Uttle information about the effect of inoculation of rats 

 or "mice with Br. melitensis, but there is reason to believe that these animals are slightly 

 susceptible to infection (see Singer-Brooks 1937). 



Monkeys may be infected either by feeding or by subcutaneous inoculation. Fre- 

 quently an intermittent fever is set up, simulating in many respects undulant fever. If 

 the animals are killed after a few weeks, there may be some enlargement of the lymph 

 glands and spleen ; occasionally necrotic lesions are found in the lungs or liver. Agglutinins 

 are demonstrable in the serum, and the organisms can often be recovered from the tissues 

 (see Bruce 1893, Hughes 1893, Horrocks and Kennedy 1906, Huddleson and Hallman 

 1929, Weigmann 1931, Zeller, Beller, and Stockmayer 1934). 



(References to pathogenicity of Br. melitensis for small animals : Durham 1898, Eyre 

 1905, 1908-09, NicoUe and Conseil 1909, Burnet 1922, Zdrodowski et al. 1930, Rainsford 

 1933.) For reproduction of disease in larger animals see Chapter 75. 



