COLD AND VIRUS INFECTIVITY 



SIMULTANEOUS MEASUREMENTS OF VIRUS, INHIBITOR, AND 

 ENZYME LEVELS DURING INFLUENZA INFECTIONS 



In order to examine the effect of low temperature upon virus in- 

 fectivity, studies were directed toward the relationships existing be- 

 tween virus multiplication, enzyme production, and inhibitor levels 

 in the infected host. The relationships were determined first at the 

 normal environmental temperature of the host and secondly at sub- 

 normal temperatures. Both the chick embryo and white mouse were 

 used as experimental hosts .Special attention was given to A2 strains, 

 several of which had been isolated from fatal human cases of influ- 

 enza.^ In addition, A and Al strains were used. The enzyme activity 

 of the different strains varied from the Al which possessed low 

 reactivity, to the A strains which varied from low to intermediate 

 reactivity, to the A2 strains which had the greatest activity. 



A typical experiment using the chick embryo was conducted as 

 follows. Ten-twelve day embryos were injected via the allantoic 

 fluid with 0.1 ml volumes of virus of known concentration. A similar 

 number of control embryos were injected in the same way with the 

 same volume of diluent. Control and test embryos were incubated at 

 36° C to 37° C and 20° C. Six to ten embryos from each group were 

 removed at regular intervals following injection, the allantoic mem- 

 branes were harvested, washed, and weighed, and 50 per cent sus- 

 pensions were then prepared, Aliquots of the suspensions were 

 rapidly frozen and stored at -70° C. The membrane suspensions 

 were examined for their virus content by means of chick embryo 

 LD5Q titrations. The enzyme content was determined by TBA or IR 

 assay, and the inhibitor level was measured using indicator virus. 



The result of a typical experiment conducted at 37° C using A2 

 strains was as follows. Virus multiplication was indicated by a 

 steady increase indetectable virus after 1 hour. Beginning at 4 hours 

 the inhibitor content of the membranes began to decline and con- 



1 Obtained through the courtesy of Dr.R.Q. Robinson, International Influenza Center for 

 the Americas, Communicable Disease Center, US Public HealthService, Atlanta, Georgia, 

 and Dr. A. F. Rasmuss»en, Jr., University of California Medical Center, Los Angeles, 

 California. 



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