Bornaviruses are enveloped RNA viruses of the Family Bornaviridae. Borna disease virus 1 (BoDV-1) is known as the causative agent of Borna disease, an often fatal neurologic disease of horses, sheep and other domestic mammals. In 2015, the variegated squirrel bornavirus (VSBV-1) was discovered in holdings of exotic squirrels in Germany. Both viruses are zoonotic pathogens that can be transmitted to humans and cause fatal encephalitis.
The research consortium ‘ZooBoCo’ investigates aspects of laboratory diagnosis, epidemiology, pathogenesis, and prevention of zoonotic bornavirus infections. The research aims at establishing a comprehensive risk analysis for animals and humans. The consortium is coordinated by the Friedrich-Loeffler-Institut (FLI) and funded by the Federal Ministry of Education and Research (BMBF).
Website of the ZooBoCo project (in German language)
Borna Disease Virus 1 (BoDV-1)
BoDV-1 is the causative agent of Borna disease (BD), which is known since the 19th century as a sporadically occurring meningoencephalitis of domestic mammals, mainly horses, sheep and New World camelids.
The only known natural reservoir is the bicoloured white-toothed shrew (Crocidura leucodon). Whether additional species may also serve as a reservoir for BoDV-1 remains elusive. BoDV-1 establishes life-long persistence in infected bicoloured white-toothed shrews without causing disease. Infectious virus is excreted via urine, faeces, saliva and skin. The endemic area of BoDV-1 in shrew populations is restricted to parts of Eastern and Southern Germany, Austria, Switzerland and the principality of Liechtenstein.
Non-reservoir mammals, such as horses, sheep and humans, may be infected by spill-over transmission from the reservoir host and serve as erroneous dead-end hosts of the virus. In these hosts, the virus is strongly neurotropic and restricted almost exclusively to the central nervous system, leading to severe and often fatal encephalomyelitis. Infected dead-end hosts do not shed infectious virus and the virus is usually not detectable in their blood. Natural BoDV-1 transmission from infected horses, sheep or humans to other mammals has not been documented so far.
In the 1990s, BoDV-1 was controversially discussed as being distributed worldwide and causing psychiatric disorders in humans. However, scientific evidence could not be provided for this hypothesis. The first reports on unequivocally confirmed BoDV-1 infection in humans, resulting in fatal encephalitis, were published in 2018.
variegated squirrel bornavirus 1, VSBV-1
VSBV-1 is genetically related to BoDV-1 and was first described in 2015. It was detected in variegated squirrels (Sciurus variegatoides), Prevost´s squirrels (Callosciurus prevostii) and few individuals of other exotic squirrel species that were kept as pet animals in Germany, The Netherlands and Croatia. In few cases, transmission of VSBV-1 from squirrels to their breeders or animals caretakers was confirmed, leading to severe and mostly fatal encephalitis.
Due to this zoonotic risk, the FLI recommends regular testing of all squirrel holdings for VSBV-1. The virus was neither detected in free-ranging Eurasian red squirrels (Sciurus vulgaris) nor in other wild animals in Germany. The range of potentially susceptible host species is currently investigated as part of the ZooBoCo project.