INFECTIOUS VESICULAR STOMATITIS 385 



overlooked and the disease thus permitted to become enzootic 

 or even epizootic. 



Etiology. — ^The cause of infectious vesicular stomatitis is 

 unknown. During the stage of vesicular eruption it seems 

 most transmissible. Fresh vesicular fluid strained through 

 a Berkefeld filter loses its infectious properties. The virus 

 therefore is evidently not filtrable. Susceptible horses 

 may become infected by inoculation with the fluid contained 

 in the vesicles of diseased animals. Frequently, however, 

 inoculation experiments will fail to develop the infection. 

 In one experiment made by the Bureau of Animal Industry 

 the disease was successfully transmitted to only three out of 

 nine animals inoculated. This experience has led some 

 observers to believe the disease non-communicable. The 

 virus is probably short-lived and is transmitted only by close 

 contact. The disease does not seem to spread from one 

 corral to another, provided a double fence separates the two. 

 A field which had contained cases of infectious vesicular 

 stomatitis did not infect horses and cattle placed therein 

 three weeks later. Susceptible animals did not become 

 infected when placed in a stable which sixteen days before 

 had housed active cases. 



Transmission through intermediary agents does not seem 

 common. Direct contact seems necessary for spread from 

 animal to animal. Inoculation experiments on rabbits, 

 guinea pigs, rats and mice, resulted negatively. 



As far as is known one attack produces immunity for at 

 least three months. Blood serum, however, from immune 

 animals failed to produce resistance to the disease when 

 injected into susceptible animals. The milk of infected 

 cattle has been fed to hogs without ill effect. 



Symptoms. — ^The period of incubation is usually two to five 

 days. A minimum period of thirty-six hours and a maximum 

 of nine days have been recognized. The initial symptoms 

 consist in the appearance of red areas in the mucous mem- 

 brane of the mouth especially the tongue. There rapidly 

 develop vesicles of grayish-red color, slightly elevated, filled 

 with a clear or yellowish fiuid and varying in size from a ten- 

 cent piece to a silver dollar. Smaller vesicles by coalescence 

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