title: RNA virus populations as quasispecies.
abstract: RNA virus mutation frequencies generally approach maximum tolerable levels, and create complex indeterminate quasispecies populations in infected hosts. This usually favors extreme rates of evolution, although periods of relative stasis or equilibrium, punctuated by rapid change may also occur (as for other life forms). Because complex quasispecies populations of RNA viruses arise probabilistically and differentially in every host, their compositions and exact roles in disease pathogenesis are indeterminate and their directions of evolution, and the nature and timing of "new" virus outbreaks are unpredictable.
authors.affiliation: Department of Biology, University of California, San Diego, La Jolla 92093-0116.
authors.forename: J J
authors.initials: JJ
authors.lastname: Holland
authors.forename: J C
authors.initials: JC
authors.lastname: De La Torre
authors.forename: D A
authors.initials: DA
authors.lastname: Steinhauer
mesh_terms: D005075:Biological Evolution; D006801:Humans; D009154:Mutation; D012328:RNA Viruses / Q000235:genetics* / Q000472:pathogenicity; D013045:Species Specificity; D014777:Virus Diseases / Q000209:etiology