"MASKING," TRANSFORMATION, AND INTEREPIDEMIC 

 SURVIVAL OF ANIMAL VIRUSES 



Richard E. Shope 



Merck Institute for Therapeutic Research 



Rahway, New Jersey 



The opportunity of discussing some of the animal virus problems 

 with a group of investigators skilled in the bacterial and plant virus 

 fields is an extremely welcome one to me personally. In reading bac- 

 teriophage or plant virus papers, I have often found myself secretly 

 wishing that our animal virus field could be reduced to the same simple 

 and direct experimental approach frequently employed by phage and 

 plant virus investigators. 



There are several good and probably insurmountable reasons why 

 this desirable state of affairs will never be achieved and why observa- 

 tions made with the bacterial viruses and the plant viruses will never 

 be exactly and completely applicable to the animal virus field. For 

 one thing the experimental hosts used by the bacteriophage and plant 

 virus people have no circulating antibodies to foul up the efforts of 

 researchers. While the immune response serves a very useful and 

 practical purpose in the animal virus field, it does render impossible 

 any strictly comparable in vivo comparisons between the behavior of 

 animal viruses on the one hand and bacterial and plant viruses on the 

 other. Of less importance, but still fairly serious in modifying the out- 

 come of work with the animal viruses, are the roles played by cellular 

 immunity, complications caused by unrecognized interfering infections, 

 and the as yet poorly understood influence of the host's nutritional 

 state on the course and outcome of animal virus infections. These are 

 factors which play no or only a very minor role in work with the plant 

 and bacterial viruses. 



In pointing out these things, I am not trying to furnish an alibi 

 for investigators of the animal viruses but merely endeavoring to in- 

 dicate why some of our observations cannot be as beautifully clear cut 

 as are many of those with bacteriophage or with certain of the plant 

 viruses. I am very much inclined to agree with what Liiria wrote in 

 his statement concerning bacteriophage that the very fact that many 

 of the gaps in our knowledge of viruses can be clearly visualized and 

 delimited in phage analysis suggests that they may be filled more easily 

 by work on bacteriophage than on other biological systems. Borrow- 

 ing further from Luria's statement it is questionable how much light 

 phage research can throw specifically on the events of other virus 

 infections in that virus-host relationships may include systems so dif- 

 ferent that the findings with one will be only relatively indirectly 

 applicable to the other. Bearing in mind the possibility that the com- 



