INFECTIOUS DISEASES 841 



it has appeared in the United States on six different occasions: in 

 1870, 1880, 1884, 1902, 1908 and 1914. 



- Etiology. — Foot-and-mouth disease is produced by one of the so- 

 called filtrable viruses, which up to the present time has not been suc- 

 cessfully cultivated outside of the animal body. The virus exists 

 especially in the serous fluids of the vesicles in the mouth, from which 

 it gains entrance to the saliva and thus to the soil and food from the 

 salivary secretions. The vesicular lesions are also found on the feet 

 and thus the virus also gains entrance to soil, bedding and food, from 

 which other animals can easily obtain infection. There appears to be 

 little doubt but what the virus is eliminated from the body in all excre- 

 tions. The exact length of time the virus will retain its vitality 

 outside of the animal body has not been determined, but it has been 

 observed that infection will persist in buildings that have not been 

 disinfected for several months. Some outbreaks of this disease have 

 b:en apparently traced to contaminated hay that had not been in con- 

 tact with diseased animals for three months or more. Thus infection 

 may be obtained from food, infected premises, hides and in the various 

 animal serums. 



In the 1914 outbreak in the United States several centers of infection 

 were undpubtedly established through the use of anti-hog cholera 

 serum that had been made from infected hogs. This latter source is 

 of considerable importance and should entail careful inspection upon 

 the part of the government employes to prevent a distribution of the 

 disease by this means. 



The usual channel of entrance of infection is through the abrasion 

 of the buccal mucous membrane, but in hogs the infection is more fre- 

 quently affected through abrasion of the skin in an interdigital space 

 or around the superior part of the hoof. Such abrasions are no doubt 

 of very common occurrence as they can easily be produced by stubs, 

 sticks and splinters which are very common in the pens where hogs are 

 maintained. Infection can also be introduced upon food stuff, es- 

 pecially by milk 'from affected cows and thus gain entrance to the le- 

 sions to abrasions in the mouth, and as before stated infection may be 

 introduced in serum. Some authorities are of the opinion that the dis- 

 ease may be carried from farm to farm by birds and other carrion 

 animals; hence an absolute quarantine should be maintained on al! 

 infected premises. 



