Rotaviruses are a genus of viruses belonging to the Reoviridae family. They have a genome consisting of 11 double-stranded RNA segments surrounded by a distinctive two-layered protein capsid. Particles are up to 100 nm in diameter and have a buoyant density of 1.36 g/ml in CsCl. Six antigenic groups have been identified, three of which (groups A, B, and C) infect humans.