Direct evidence for genome segment reassortment between concurrently-circulating human rotavirus strains

Extensive heterogeneity in electropherotypes observed among group A human r otaviruses has been considered as a result of two major mechanisms; i.e., t he accumulation of point mutations and genetic reassortment between concurr ently-circulating strains. However, no evidence was reported thus far indic ating that any one of field isolates of rotavirus was formed by direct reas sortment of concurrently circulating two parental strains. Comparison of th e genome of human rotavirus specimens collected over a six year period by e lectropherotyping and by the sequencing of selected gene segments identifie d two reassortants that were generated in nature between strains circulatin g co-dominantly in the same epidemic season. This is the first report direc tly showing that at least some part of electrophoretic diversity observed a mong rotavirus strains was explained by genetic reassortment between strain s concurrently circulating in the human population. This supports the hypot hesis that genetic reassortment among co-circulating strains operates as a key mechanism for the genetic variability of rotaviruses in nature.