404 Microbes and You 



pox group diseases (Borreliotaceae), encephalitis diseases (Er- 

 ronaceae), vellow fever group (Charonaceae), infectious anemia 

 group ( Trif uraceae ) , and the mumps group ( Rabulaceae ) . 



A discussion of all virus diseases is impractical in a book of this 

 type, but a brief consideration of a few of the more common 

 diseases of man will be presented. 



Smallpox 



This serious disease is known technically as variola, and it used 

 to be the cause of much misery, disfigurement, and high death 

 rates before the advent of mass vaccinations. The first vaccination 

 was performed by Edward Jenner in 1798. This pioneer made the 

 astute observation that manv persons associating with cows suffer- 

 ing from cowpox, did not become affected during severe epidemics 

 of smallpox. He reasoned that cowpox (vaccinia) was in some 

 way related to smallpox. To confirm his suspicions Jenner intro- 

 duced some lymph from the pustules found on the udder of an in- 

 fected cow into a scratch made on the arm of a human being. 

 The mild disease, vaccinia, resulted in the formation of a single 

 pock mark at the site of the scratch on the arm. Once infected 

 with cowpox these individuals did not contract the more serious 

 smallpox. Cowpox is smallpox that has become modified by 

 passage through a lower animal, and while the virus loses its lethal 

 virulence, its vaccinating power (antigenicity) is not impaired. 



The smallpox vaccine used to prevent this disease today is pre- 

 pared by introducing cowpox virus into the shaved and disinfected 

 skin surface on the abdomen of a calf. After suitable incubation 

 the lymph formed in these pustules is harvested and tested for 

 potency and purity before being tubed for use in vaccinating hu- 

 mans. Smallpox vaccine can also be prepared in test tubes as 

 tissue cultures, and in embryonated eggs, each of which has a de- 

 cided advantage over the calf method in that bacterial contamina- 

 tion can be more effectively controlled. 



Smallpox vaccination lasts for about five years, but some 

 persons become susceptible in shorter periods of time while others 

 remain immune for life. Mass vaccination is advisable during^ im- 



