Infections Caused by Bornaviruses

Bornaviruses (Mononegavirales: Bornaviridae) form enveloped virions with nonsegmented, single-stranded negative-sense genomes (∼8.9 kilobases). They naturally infect mammals (e.g., bicolored white-toothed shrews [Crocidura leucodon], equids, sheep, variegated squirrels [Sciurus variegatoides] but rarely other mammals including humans) and a wide variety of birds and snakes. Bornaviruses have unique characteristics, such as 1) replication in the nucleus using cellular splicing machinery for generation of mRNAs and integrating bornaviral elements into the host-cell genome; 2) genome trimming for generation of RNAs that probably do not trigger innate immune responses in infected cells; and 3) suppression of apoptosis in infected cells mediated by the accessory protein (X), leading to persistent noncytolytic infection.