TEMPERATURE AND VIRAL INFECTION 



ticularly interesting question, there seems to be relatively little 

 data that concerns such infections and involves hosts and viruses 

 that lend themselves to detailed study. Dr. Andrewes has already 

 dealt with the common cold in man. There is one study, however, 

 that should be mentioned here, 



Shope has pointed out that circumstantial evidence concerned with 

 epizootics of swine influenza has long indicated that the stimulus 

 responsible for precipitating attacks of the disease in swine latently 

 infected with the virus is in some way associated with sudden 

 changes in weather and especially with the onset of cold,wet weather. 

 He performed an experiment (Shope, 1955) in which he prepared 25 

 swine by feeding them earthworms containing lungworm larvae 

 carrying swine influenza virus. After about 30 days, during which 

 the animals remained well, he then exposed them for from 4 to 24 

 hours to adverse weather conditions, which always included rain or 

 snow and low temperatures. No data were obtained on the effect of 

 this on the body temperatures of the animals. Eight uninoculated 

 controls and 15 inoculated animals remained well, but 4 swine did 

 develop the typical illness of swine influenza and 6 others developed 

 serological evidence of infection. 



POSSIBLE MECHANISMS FOR THE 

 EFFECT OF COLD ON VIRAL INFECTIONS 



The studies that I have outlined indicate that with some hosts and 

 viruses under proper circumstances cold can aggravate and activate 

 viral infections. I have limited discussion here to those studies that 

 do point to these possibilities, because I think failures to find an 

 aggravating effect of cold, or even the occasional report of the op- 

 posite effect, are only to be expected with some host- virus combina- 

 tions and under certain circumstances. But the fact that there are a 

 good many reports of no effect or a protective effect of cold must be 

 kept in mind in any evaluation of possible mechanisms. I shall dis- 

 cuss this further in a later section. 



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