Reoviruses are infectious agents, transmitted by respiratory and faecal – oral routes. The mammalian reoviruses (MRV) are the prototypic viruses of a large group of infectious agents, many of which are highly pathogenic to their natural hosts, although the MRV are not significant human pathogens. The MRV are distinguished by having a genome of 10 segments of double‐stranded ribonucleic acid (dsRNA) that is located inside a double‐layered, spherical nonenveloped protein capsid. The capsid is incompletely uncoated during viral replication and the inner capsid (core) serves as an enzymatic ‘machine’ producing progeny mRNA. The virus is being studied as a potential anticancer oncolytic therapy. The virus is also quite stable and therefore is useful as a ‘bio‐indicator’ for assessing water quality and wastewater disinfection.

Key Concepts:

  • The reoviruses have served as models for understanding biology of double‐stranded RNA and RNA transcription signals.

  • Mammalian reoviruses are ubiquitous in nature and virtually all mammalian species are infected by these agents.

  • Reoviruses have a segmented genome and different genome segments from different virus types can mix to create hybrid progeny viruses called ‘reassortants’.

  • Although most family members are highly pathogenic in their natural hosts, mammalian reoviruses are generally harmless to humans.

  • Because the viruses are generally harmless, and because they are unusually stable, they serve beneficially as anticancer agents and for monitoring water and wastewater disinfection.

Keywords: RNA virus; dsRNA; gastroenteritis; RdRp; reassortant

Figure 1.

RNA profiles (electropherotypes) of reovirus T1L, T2J and T3D. RNA segments were resolved in a 10% polyacrylamide gel, stained with ethidium bromide and photographed. The identities of individual genes are indicated on the left (T1L) and right (T3D) of the gel. Note that migration of gene segments M1/M2 and S3/S4 are reversed. The segmented nature of the viral genome has important implications in type variation, and the differences in migration rates of each gene are exploited in genetic experiments.

Figure 2.

Structure of reovirus, serotype 1 Lang (T1L). (a) Cryoelectron microscopic reconstructions of the reovirus virion (virus), the intermediate subviral particle (ISVP) and the core. (Reprinted from Spencer et al., . Copyright 1997, with permission from Elsevier. Images were recolorised with Adobe Photoshop software to facilitate comparison with colours in (c) and (d)). (b) Cartoon of genome profile of T1L in polyacrylamide gel, representing the profile shown in Figure (left panel). Gene segments (L1–S4,S3) are indicated on the left. (c) Cartoon of protein profiles of virus, ISVP and core in sodium dodecyl sulfate–polyacrylamide gel. Each protein is encoded by the indicated gene segment in (b) (arrows). Proteins are colour‐coded to facilitate their identification in (a) and (d). Note that protein σ3 is removed from particles, and protein μ1 is cleaved into peptides δ and ϕ, when the virion is converted into the ISVP. The precise locations of peptides δ and ϕ may be inferred from recent atomic structures but are not indicated in this cartoon. Peptides σ1, δ and ϕ are removed when the ISVP is converted into the core. Identification of known cognate avian reovirus proteins are indicated in parentheses to the right of the mammalian reovirus protein names. (d) Composite cartoon of reovirus virion, ISVP and core, showing presumptive locations of various structural proteins, and their conversion or removal from each type of particle. Protein colours are the same as in (a) and (c); coloration or shape of proteins λ2, μ1 and δ change from virus‐ISVP‐core to represent known dramatic conformational changes.

Figure 3.

Reovirus replicative cycle. Details are provided in the text. Steps are: (1) binding, (2) entry, (3) membrane interaction, (4) uncoating, (5) initial capped transcription, (6) initial translation, (7) primary capped transcription, (8) primary translation, (9) assortment, (10) synthesis of negative RNA strands, (11) generation of transcriptase complex, (12) secondary uncapped transcription, (13) secondary translation, (14) assembly of outer capsid and (15) release. Dashed green arrows indicate transcription events leading to production of mRNAs (indicated in grey boxes), dotted red arrows indicate translation events leading to production of proteins (indicated in white ovals) and black arrows indicate movement of proteins and viral complexes. An alternate entry mechanism for intermediate subviral particles (ISVPs) is shown with white arrows at the top and in step 3a.



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Further Reading

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Coombs, Kevin M(Feb 2011) Reoviruses. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001084.pub3]