Interference Mediated by a Variant of Sindbis Virus. I. Isolation of an Avirulent Variant and In Vivo Interference

Abstract

A newly recognized, avirulent large-plaque (ALP) variant of Sindbis virus failed to kill suckling mice after intracerebral inoculation and replicated at the site of inoculation to a lower titer than virulent strains. When this variant was mixed with virulent large-plaque (VLP) or virulent small-plaque (VSP) variants of Sindbis virus or with chikungunya virus and inoculated into suckling mice, the ability of the virulent viruses to kill suckling mice was inhibited. ALP also transiently inhibited replication of VSP in brains of suckling mice. ALP was shown to be ether-sensitive; its infectivity and its interfering effect were neutralized by sera immune to Sindbis. Under conditions of the interference test, ALP induced interferon more rapidly than virulent strains of Sindbis virus.