WALKER 



Studies concerned with the effect of environmental temperature on 

 viral infections have sometimes been confusing and seemingly con- 

 tradictory, but cold has most often been found to aggravate viral in- 

 fections. For the purposes of this symposium, then, it seems to me 

 that there are four questions that should be considered: 1) Can ex- 

 posure to cold cause a mild, inapparent viral disease? 2) Can this 

 exposure seriously worsen an apparent viral infection? 3) Can it 

 activate a latent viral infection? 4) What are the mechanisms by 

 which cold exerts its effect on viral infections? 



It is difficult to find direct experimental data bearing on these 

 questions that have been obtained in studies of infections in man, but 

 some evidence is available from studies in animals, and some in- 

 formation is available from study of viral infection of cells in 

 culture. The data are not extensive, but I think they provide indi- 

 cation that the answers to the first three questions can be yes, at 

 least with selected virus-host systems and under laboratory con- 

 ditions, perhaps even in man, and that we may find such effects if 

 we make the proper search. 



I should like, then, to disclose this evidence. Some of it is from 

 others, but I shall limit consideration to that which I think has a 

 quite direct bearing on the questions that I have posed. 



EXAMPLES OF THE EFFECT OF COLD ON VIRAL INFECTION 



Can Exposure to Cold Cause a Mild, Inapparent Viral Infection to 

 Become an Apparent and Serious Disease? 



Boring and I have studied a model viral infection in mice caused 

 by the Conn.- 5 strain of type Bl Coxsackie virus (Boring, ZuRhein, 

 and Walker, 19 56; Walker and Boring, 1958). Although this virus 

 produces a generalized and lethal infection in infant mice, it causes 

 in adult Swiss mice only a pancreatitis. The mice seldom show out- 

 ward signs of illness even after very large inocula. However, when 



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