CASEOUS LYMPHADENITIS OF SHEEP 451 



CASEOUS LYMPHADENITIS OF SHEEP. 



Cheesy Bronchopneumonia of Sheep. Psetjdo- 



TUBEECULOSIS OF ShEEP. 



Definition.— Caseous lymphadenitis is an infectious disease, 

 due to a specific bacillus, which sometimes manifests itself 

 as a subacute or chronic bronchopneumonia and at other 

 times occurs as an affection of the superficial lymph glands. 



Occurrence. — ^The disease appears in the form of an 

 epizootic in the western part of the United States, where it 

 induces, especially among lambs, a large mortality, over two- 

 thu-ds of the lambs dying of the disease. It therefore attains 

 economic importance. The disease is not uncommon in 

 Europe, Australia, and in the Argentine Republic. 



Etiology. — The cause is the Bacillus pseudotuberculosis 

 ovis, a non-sporebearing, immotile rod which may be easily 

 stained with anilin dyes. It also stains according to Gram. 

 The germ is pathogenic to swine, guinea pigs, and rabbits. 

 Pigeons and fowls are not very susceptible. 



Natural Infection. — Infection probably takes place through 

 the digestive tract, although it may enter through wounds 

 (docking, castration), or the unshrivelled navel of young 

 calves. The droppings of infected sheep contain the bacillus 

 in large numbers, and therefore form an important factor 

 in spreading the disease. 



Necropsy. — ^The principal lesions are found in the lungs, 

 lymph glands of the thorax, and the external lymph glands. 

 Throughout the lung tissue nmnerous small, gray or grayish- 

 green nodules occur which through coalescence may form 

 large, cheesy areas. There is frequently also present an 

 adhesive pleuritis. The corresponding lymph glands may 

 be intact. In many cases the lesions are confined to the 

 external lymph glands, which are enlarged, and when incised, 

 show greenish-yellow, sticky, smeary, cheesy masses often 

 arranged in concentric layers and surrounded by a capsule 

 of connective tissue. Often the caseous mass undergoes 

 partial calcification changing it to a grayish-white, gypsum- 

 like mass. In rarer instances the abdominal organs are 



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