320 ACUTE GENERAL INFECTIOUS DISEASES 



which may permanently impair the efficiency of the horses 

 attacked, it can assume even greater economic importance. 



Etiology. — The cause of infectious pneumonia of the horse 

 has not yet been identified. According to Gaffky and Liihrs 

 the bronchial slime of an infected patient contains the virus 

 of the disease, at least in the early stages. In typical cases of 

 infectious pneumonia in which the patients were destroyed on 

 the third or fourth day, in the bronchi was found a quantity 

 of yellow, transparent, viscid fluid which contained no bac- 

 teria. In two experiments on twenty-four colts inoculated 

 with this fluid, by painting it upon the mucosa of the nostrils 

 and in the mouth, the colts became typically ill with infectious 

 pneumonia in twenty-three to forty-two days. Undoubtedly 

 a specific virus, which may be filterable, forms the true cause 

 of the disease. In all probability, however, other bacteria, 

 principally the Streptococcus pyogenes equi, and the Bacillus 

 equi septicus, are secondary invaders, contributing to the 

 underlying disease process and clinical phenomena. 



Natural Infection. — The way in which the disease spreads 

 naturally is at present not known. The infection seems to be 

 spread by more or less intimate contact between the sick 

 horse and susceptible ones. The transmission through inter- 

 mediate agents, such as food, water, stable utensils, etc., or 

 through persons or insects, has not been demonstrated experi- 

 mentally. However, practical experience in other diseases 

 and with this disease would not exclude indirect transmission. 

 Sporadic outbreaks in stables could be explained, however, as 

 coming from apparently healthy "germ carriers" or "missed 

 cases" of infectious pneumonia, i. e., where still exist in the 

 lungs or occasionally in other organs unhealed foci of infection. 

 As predisposing factors anything which reduces the resistance 

 of the susceptible animal unquestionably has a bearing on the 

 origin of the disease. Therefore refrigeration, overwork, bad 

 sanitary conditions, become predisposing factors. The dis- 

 ease is rare in very young or aged horses, and occurs usually 

 in animals in the prime of life. 



One attack produces immunity for only a short period. 

 Individual instances are recorded in which a given horse has 

 suffered repeated mild attacks of the disease, An attack 



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