Members of the family Reoviridae have striking icosahedral or quasi-spherical virions (Fig. 34-1), with two concentric icosahedral capsids surrounding an inner core. The virions of rotaviruses and orthoreoviruses are relatively stable to heat and to pH 3, and their infectivity is actually increased by exposure to proteolytic enzymes encountered in the gut. The genome comprises 10-12 unique molecules of dsRNA, total size 18-27 kilobase pairs, depending on the genus (Table 34-1). The positive strands of each duplex are 5' capped and the negative strands 5' phosphorylated; the 3' termini are not polyadenylated. Genera share no antigens, but within genera there are genus-specific and species-specific antigens.
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