Capsid symmetry of viruses of the proposed Birnavirus group.

The capsid architecture of three members of the tentatively formed group of bisegmented ds RNA containing animal viruses (Birnavirus group) was studied in comparison with the fine structure of reovirus type 1 using high resolution negative staining and shadowing techniques followed by rotational enhancement analysis. IPNV of the trout, IBDV of the chicken, and eel virus (Berlin) are single-shelled particles with a capsid diameter of 61-65 nm and thus clearly distinguishable from the double-shelled reovirus being 80-85 nm in size. The capsid symmetries of both groups of viruses are skew, with a triangulation number T=13. The handedness of the capsid is dextro for IBDV and EV, and laevo for IPNV and reovirus type 1.