Dicistroviruses

The Dicistroviridae are a family of small icosahedral viruses with single-stranded RNA, positive-sense genomes that infect invertebrates. The genomes are organized with their nonstructural proteins encoded at the 5′ end with the structural proteins at the 3′ end. Characteristically, the two open reading frames are separated by an untranslated region that is capable of acting as an internal ribosome entry site (IRES). In addition to the structural proteins being expressed from this IRES, translation usually initiates from a noncanonical amino acid, generally alanine. The dicistroviruses share a number of characteristics, for example, virion structure, genomic organization, and the absence of subgenomic RNAs with other picorna-like viruses of plants, animals, and protists that suggest a shared evolutionary origin and a higher-order taxonomic grouping for such viruses. Most dicistroviruses, with the exception of cricket paralysis virus (CrPV), have restricted host ranges and only infect species from a single insect order. In contrast, CrPV is able to infect over 20 species of insects and several insect cell lines. Most dicistroviruses have vertical and horizontal components in their transmission and generally produce few noticeable disease symptoms. Infection with dicistroviruses does, however, usually result in a shortened life span and reduced fecundity of the host.