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.