The virus particles are spherical and have an average diameter of 110-130nm. Viewed in cross-section, they show grainy particles which are ribosomes acquired from host cells. Genetic organization differs from Toga's - structural proteins at 5' end of genome, N.S. at 3' end. All 3 RNA species are linear, but in the virion, appear circular because the ends are held together by base-pairing. Replication is similar to that of Phleboviruses.
Assembly occurs at the cell surface, and the envelope is acquired as the virus buds from the cell.
Release and maturation almost simultaneous. Cellular receptors are not known - obviously widely distributed. Glycoprotein spikes are responsible for receptor binding - antisera neutralize attachment. Assembly occurs during budding, characteristically into cytoplasmic vacuoles rather than the cell surface as Toga's. Release occurs when cell lyses.