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 cow-pox is a very common disease in 

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

 been reported. In Asia, Africa and in parts of Europe 

 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 

 cow-pox (variola vaccina) and smallpox of man (variola 

 humana), although if man be inoculated with cow-pox, 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 cow-pox, 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 cow-pox 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. Goat-pox 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 cow-pox, 

 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 goat-pox (variola caprina) are independent diseases, while 



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