372 DISEASES LOCALIZED IN CERTAIN ORGANS 



are infected. In the Philippine Islands the disease is wide- 

 spread. 



Etiology. — Lung plague is due to a very minute micro- 

 organism which passes through coarse porcelain filters but 

 may be seen under the microscope when magnified over 1500 

 diameters. It is the smallest visible microorganism as yet 

 known, being almost ultramicroscopic. The organism has 

 been grown in artificial media. The virus is found in the . 

 pleural exudate, diseased lung and in nasal discharge. The 

 blood rarely is infectious. 



Natural Infection. — Probably through the respiratory tract. 

 Experiments to produce typical lung plague in susceptible 

 animals by inhalation or feeding have not been successful; 



The disease spreads usually by direct contact with infected 

 animals. Infected and emptied stables in which within a 

 year sick cattle had been kept are common sources of infec- 

 tion. Where cattle are crowded together in a barn the dis- 

 ease spreads most rapidly. On the other hand, however, a 

 rapid spread among cattle on pasture has been frequently 

 noted. 



Very commonly a supposed recovered ox with an encap- 

 suled lung focus is the infecting agent. So long as the se- 

 questered centre in the lung is completely encysted, no virus 

 will be thrown off, but once a communication is established 

 with a bronchus giving the virus exit the patient becomes a 

 source of danger to healthy cattle. The virus may remain 

 virulent for two or three years in a lung sequestrum of an 

 apparently healthy ox. 



The disease is more prevalent in stable-fed than among 

 pastured animals. It affects all breeds, although some indi- 

 viduals possess natural immunity. 



Necropsy. — As a rule only one lung (left) is involved. Usu- 

 ally a large area is hepatized. On cross-section a clear, yellow 

 fluid, which quickly coagulates flows over the cut surface. 

 The interlobular connective tissue is greatly thickened, form- 

 ing yellow, gelatinous strands one-half inch or more in 

 thickness, which divide the lung tissue into islands of varied 

 color. Characteristic of the lung lesions are the different 

 degrees of inflammation which appear at the same, time fresh 



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