Abstract
Summary
A method of testing the effect of various factors on the mouse virulence of the type III poliovirus was described. Variants of the virus which could be made virulent or avirulent were isolated. The virus was designated as LH-v in its virulent phase and LH-a in its avirulent phase. Using these variants as testing tools, 3 factors affecting the viral virulence were found; namely, the host cell, the maintenance medium, and the pH of the medium. These factors were classified into 2 categories, namely the virulence reducing group and the virulence enhancing group. When tested with monkey kidney cell cultures in the pH range 7.0–7.5, Eagle's basal medium and 199 medium belonged to the virulence enhancing group while Medium E (bovine plasma hydrolysate) and lactalbumin hydrolysate medium belonged to the virulence reducing group. When tested in Medium 199 at pH 7.0–7.5 monkey kidney cells enhanced the viral virulence while HeLa cells behaved in the opposite way.
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