Chapter X 



Serological Variation 



T. Francis, Jr. 

 University of Michigan, Ann Arbor, Michigan 



I. Introduction 251 



II. Serological Reagents 252 



III. Serological Variation among Influenza Viruses 253 



A. Viral Structure 253 



B. Serological Types 254 



C. Antigenic Analysis of Type A Strains 254 



1. Studies with Sera of Experimental Animals 254 



2. Studies with Human Sera 260 



3. Classification of Type A Strains 263 



D. Variation in Type B Influenza Virus 265 



E. Serological Variation during Passage 265 



1. Adaptation to New Hosts 265 



2. Induced Variation 267 



3. Phase Variation 267 



IV. Variation in Arthropod-Borne Viruses 269 



A. Demonstration of Strain Relationships 269 



B. Value of Successive Exposure in Demonstrating Relationships hi Virus 



Groups 269 



References 270 



I. Introduction 



Actual demonstration of serological variation and immunological relation- 

 ship among viruses has been frequently predictable from epidemiological 

 observations of the behavior of a disease and its associated immunity. The 

 protective effect of cowpox against smallpox, the recognition of alastrim, 

 the development of vaccinia virus, and the knowledge of similar 

 diseases in a variety of animals presented an array of circumstances inviting 

 speculation and research into the nature of these variations. A groundwork 

 was laid for consideration of a stem virus developing a variety of mutants 

 under the influence of different hosts. Recurrent outbreaks of foot-and-mouth 

 disease among the herds led to the first recognition of serologically distinct 

 types in the first of the identified filterable viruses. Recovery from smallpox 

 (variola major), measles, or yellow fever was, however, seen to be uniformly 

 associated with prolonged immunity, indicating a high degree of serological 

 unity in the respective viruses and also calling attention to the importance of 



251 



