Borna disease virus 1 (BoDV‑1) is a neurotropic, negative‑sense single‑stranded RNA virus that belongs to the family Bornaviridae. It is the prototype agent of Borna disease, a fatal meningoencephalitis historically described in horses and sheep in central Europe. BoDV‑1 is enveloped and non‑segmented, and unlike most Mononegavirales it replicates in the nucleus of infected cells. Natural reservoirs appear to be small insectivorous mammals, with occasional spillover into domestic animals and humans.
Genome and Virology
The BoDV‑1 genome is approximately 8.9 kb in length and encodes six major proteins: nucleoprotein (N), phosphoprotein (P), X protein, matrix protein (M), glycoprotein (G) and the large polymerase (L). The virus forms ribonucleoprotein complexes that enter the host cell nucleus where transcription and replication occur. Viral mRNAs undergo splicing and polyadenylation using host nuclear machinery, and antigenomic RNA serves as a template for progeny genomes. BoDV‑1 glycoprotein mediates attachment and fusion with host cell membranes, with entry likely involving endocytosis; the precise receptor has not been fully defined. Persistent infection is characteristic: the virus establishes long‑term replication in neurons and glial cells with minimal cytopathic effect, leading to immune‑mediated pathology. The X and P proteins interfere with interferon signalling and apoptosis, promoting viral persistence. BoDV‑1 shows remarkable genetic stability compared with other RNA viruses, suggesting long coevolution with its hosts.
Epidemiology and Disease in Animals and Humans
Classical Borna disease was first recognized in the late nineteenth century near the town of Borna in Germany. Outbreaks in horses and sheep present with ataxia, behavioural changes, paresis and high case fatality. The bicoloured white‑toothed shrew (Crocidura leucodon) serves as a reservoir; infected shrews shed virus in saliva and urine without clinical illness. Sporadic zoonotic transmission to humans has been documented in Germany, Austria and Switzerland. Since 2018, several cases of severe encephalitis caused by BoDV‑1 have been confirmed, characterized by fever, headaches, confusion, seizures and progressive coma; mortality exceeds 50 %. Diagnosis relies on RT‑PCR and serology, and treatment remains supportive. There is no licensed vaccine or antiviral therapy for animals or humans. Preventive measures focus on limiting contact with reservoir hosts and implementing biosecurity on farms. Other bornaviruses infect birds and reptiles but are genetically distinct and have different disease associations. Borna disease virus 1 exemplifies a neurotropic RNA virus that persists in its hosts and causes severe neurologic disease when transmitted to accidental hosts. Continued surveillance and experimental studies are essential to understand transmission routes, develop diagnostics and evaluate potential therapies. Related Terms: Bornaviridae, mammalian orthobornavirus 1, viral encephalitis, rabies virus, neurotropic RNA virus