Chapter II 

 The Initiation of Infection by Animal Viruses 



F. M. Burnet 



Walter and Eliza Hall Institute, Melbourne 



The first step in the process by which virus and susceptible cell interact to 

 produce a new generation of virus must necessarily be concerned with the 

 entry of the infective particle into the substance of the cell. The correspond- 

 ing sequence of events in infection of the host by a bacteriophage has been 

 intensively investigated, but in the field of animal viruses very little is accur- 

 ately known and direct experimentation has been almost wholly limited to 

 the myxovirus group. A wide range of viruses appears to be dependent on 

 some degree of traumatization to allow initiation of infection. It is character- 

 istic of mammalian and avian cells other than those exposed to the external 

 environment and its extensions that a large proportion will take in particulate 

 material nonspecifically and, provided the cell in question is susceptible, no 

 problem of a mechanism of entry arises. 



On general grounds, it is only in viruses which, to survive in nature must 

 infect intact surfaces exposed to the environment, that we might expect to 

 find specific mechanisms for the initiation of infection. Of such viruses patho- 

 genic for man, the influenza viruses and the enteroviruses, including polio- 

 viruses, have each some claim to be considered in this light. 



An immediate and characteristic difficulty of experimental virology is en- 

 countered in the dilemma that the significant characters of a virus are those 

 which have evolved to allow its survival in nature, but that the only char- 

 acters which can be accurately studied are those relevant to infection of some 

 uniform but unnatural host — the allantoic cavity or cells in monolayer tissue 

 culture. Findings from the experimental systems will undoubtedly have 

 general relevance to the problem, but they will need careful scrutiny before 

 being used to interpret clinical or epidemiological phenomena. 



Discussion of the initiation of infection of the animal cell has been domin- 

 ated by the analogies drawn from hemagglutination reactions with influenza 

 and other viruses of the group. Chapters III(I)b and IV in this volume deal 

 with biological and chemical aspects of hemagglutination, but they touch only 

 very indirectly on the mechanism of entry into the susceptible cell. In a very 

 real sense they represent accounts of what may be only two minor aspects of 

 the process that have come into prominence only because of the availability 

 of suitable experimental approaches. 



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