CHAPTER II. 

 ACUTE EXANTHEMATOUS INFECTIOUS DISEASES. 



VARIOLA. POX. 



Definition. — ^Variola is an acute contagious disease char- 

 acterized by a typical cutaneous eruption which passes 

 through the stages of papule, vesicle, pustule, and crust. In 

 all animals except sheep this eruption is usually local. 



Occurrence. — ^While cowpox is a very common disease in 

 the United States, horsepox is rare and sheep-pox has never 

 been reported. In Asia, Africa and in parts of Em-ope 

 sheep-pox becomes epizootic causing great losses. 



Etiological Relationship.- — ^The etiological relationship of the 

 pox of the different animals and of man to one another is not 

 yet clear. There is undoubtedly a close relationship between 

 cowpox (variola vaccina) and smallpox of man (variola 

 humana), although if man be inoculated with cowpox, the 

 eruption resulting usually remains local. Further, cattle are 

 not readily inoculated with smallpox. However, as is well 

 known, if man be inoculated (vaccinated) with cowpox, he is 

 protected against smallpox. Sheep-pox is transmitted with 

 difficulty to either man or cattle, natural infection does not 

 occur and no protection against cowpox is afforded cattle 

 inoculated with sheep-pox virus. Sheep-pox, therefore, is 

 probably a specific disease of sheep which does not spread to 

 other animals including goats. Goatpox affects neither man 

 nor sheep and seems to be a specific caprine disease. Horse- 

 pox is a local disease of the skin in the region of the fetlocks. 

 It is probably closely related to, if not identical, with cowpox, 

 being transmitted by recently vaccinated horseshoers to 

 horses while being shod. In the light of our present knowl- 

 edge smallpox (variola humana), sheep-pox, (variola ovina) 

 and goatpox (variola caprina) are independent diseases, while 



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