Variegated Squirrel Bornavirus 1 (VSBV‑1) is a member of the genus Orthobornavirus (family Bornaviridae) first identified in 2015 after fatal encephalitis cases in Germany. This enveloped, non‑segmented negative‑sense RNA virus has a genome of approximately 8.9 kilobases encoding at least six proteins, including nucleoprotein (N), phosphoprotein (P), matrix (M), glycoprotein (G) and RNA‑dependent RNA polymerase (L). VSBV‑1 belongs to a distinct lineage within the mammalian bornaviruses.
Classification, Biology and Pathogenesis
Bornaviruses replicate in the nuclei of infected neurons and establish persistent infections. VSBV‑1 shares genetic organisation with Borna disease virus 1 but exhibits substantial sequence divergence. Its natural reservoir appears to be exotic Sciuridae; initial investigations identified the virus in variegated squirrels (Sciurus variegatoides) kept as pets and in zoo‑housed red squirrels (Sciurus vulgaris). Transmission among squirrels may occur through bites or grooming, and vertical transmission has been hypothesised. Humans are incidental hosts. In vitro studies show that VSBV‑1 has tropism for neuronal cells and glial cells, causing non‑cytolytic infection. Infected individuals develop progressive meningoencephalitis with fever, headache, behavioural changes and rapid neurological deterioration. Histopathology reveals lymphocytic infiltration, neuronal loss and viral antigen in neurons. No specific antiviral therapy exists; treatment is supportive.
Emergence and Human Cases
The virus was first recognised when three private breeders of variegated squirrels in Germany developed fatal encephalitis between 2011 and 2013. Retrospective investigation identified VSBV‑1 RNA in archived brain tissue and linked all three cases to exposure to imported squirrels originating from Central America. Subsequent surveys detected VSBV‑1 infection in red squirrels and variegated squirrels in several European zoos and pet holdings, highlighting the risk of spillover. In 2018 a zoo animal caretaker in Germany developed meningoencephalitis and died; VSBV‑1 infection was confirmed by metagenomic sequencing. Epidemiological studies suggest that contact with saliva, bites or scratches from infected squirrels constitutes the primary transmission route. Because of the rarity of cases and high fatality, the virus is monitored by public health authorities. Preventive measures include avoiding handling exotic squirrels, using personal protective equipment when caring for captive squirrels and implementing surveillance in zoological collections. VSBV‑1 underscores the zoonotic potential of bornaviruses and the importance of monitoring the exotic pet trade. Although infections are rare, awareness among clinicians and veterinarians is essential to identify and mitigate further cases. Related Terms: Borna disease virus 1, Avian bornavirus, Mammalian orthoreovirus 1, Mammalian orthoreovirus 2, Mammalian orthoreovirus 3