ETIOLOGY 



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greater part of the United States where it received the name of 

 "pink eye" (French, ^evre typhoide). It started in Canada 

 and extended south and west, reaching into British Columbia 

 to the north and Mexico at the south. The last great epizo- 

 otic raged in Europe from 1881 to 1883 during which time it 

 is said to have spread over nearly the whole continent. In the 

 Prussian army, 3,434 horses became affected in 1890 ; 2,497 in 

 1891 ; and 3,645 in 1892. In Copenhagen, 3,000 horses were 

 affected in 1890 and 1891. 



§ 386. Geographical distribution. Influenza seems to 

 be known in nearly if not all of the countries of Europe and 

 America In certain sections of the United States it is almost 

 a constant aflfection. This is especially true of certain cities, 

 owing to the constant introduction of "green" horses. 



§ 387. Etiology. Influenza seems to be produced by a 

 specific infection the nature of which has not yet been deter- 

 mined. A number of bacteria have been described as the 

 probable cause but thus far none of them have been found to 

 be sufficiently constant to warrant their acceptance as the 

 etiological factor. It spreads rapidly among horses. The 

 virus appears to lose its virulence quickly outside of the animal 

 body, but within the body it seems to be preserved for a long 

 time. According to the observation of Jensen and Clark, 

 stallions which have had the disease may transmit it to the 

 mares they .serve for months after apparent recover}'. Dieck- 

 erhoff succeeded in transmitting the disease to healthy animals 

 by subcutaneous and intravenous injections of the blood of in- 

 fected horses, but Friedberger and Arloing failed to do so. 

 Horses are most susceptible. Sex, breed, stable management 

 and feeding appear to have little or no influence on their 

 individual susceptibility. 



Infection usually takes place from horse to horse. The 

 virus appears to be carried by infected human beings, litter, 

 harnesses and thermometers. In many cases one attack con- 

 fers immunity but a second infection or a relapse frequently 

 occurs. Toward the end of an epizootic the disease is usually 



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