412 CHRONIC INFECTIOUS DISEASES. 



Course. — The course is prolonged, extending over several 

 months. It seems to be favorably influenced by an open-air 

 life, but close confinement, advanced pregnancy, and par- 

 turition affect the course adversely. 



Prognosis. — The prognosis is bad. Cases which may be 

 recognized clinically die in a few weeks to a few months. 



Treatment. — No successful treatment has yet been devised. 

 The destruction of the diseased animals prevents further 

 spread. 



CASEOUS LYMPHADENITIS OF SHEEP. 



Cheesy Bronchopneumonia of Sheep. Pseudo- 

 tuberculosis 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- 

 thirds 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-spore-bearing, 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 unshriveled 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 numerous small, gray or grayish- 

 green nodules occur which through coalescence may form 



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