Quantitative Study on the Infectivity of Ribonucleic Acid (RNA) Isolated from Brains of Mice Infected with Eastern Equine Encephalomyelitis (EEE) Virus

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Abstract
Conditions for a quantitative plaque assay of infectious RNA isolated by phenol technique from brains of mice infected with EEE virus are described. Investigations into the effect of molarity and pH of MgSO4 solutions used as diluent in titrations and of the time of contact with chick-embryo cell monolayers on plating efficiency resulted in a procedure ensuring a relatively sensitive and reproducible RNA assay. Using a 1.125 M MgSO4 solution pH 8.0 and 15 minutes contact time, a linear dependence between the number of plaques formed and RNA dilution was obtained. The infectivities of RNA samples were about 105 lower than those of corresponding virus suspensions.