Bornaviruses are enveloped RNA viruses of the genus Orthobornavirus within the family Bornaviridae. Until a few years ago, in particular “classical” Borna disease virus 1 (BoDV-1) was known as the causative agent of Borna disease of horses and sheep. In 2015, a novel virus was detected in exotic squirrels, variegated squirrel bornavirus-1 (VSBV-1). Both bornaviruses can be transmitted to humans and are therefore considered as zoonotic pathogens.
The research consortium „ZooBoCo“ investigates aspects of diagnostics, epidemiology, pathogenesis, and prevention of zoonotic bornavirus infections with the aim to establish an extensive 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).
Homepage des Projektes ZooBoCo (in German language only)
„Classical“ Borna Disease Virus 1 (BoDV-1)
BoDV-1 is the causative agent of Borna disease of animals, a rare chronic progressive inflammation of the brain (meningoencephalitis), which mainly occurs in horses and sheep and has been known since the 19th century.
The natural reservoir of BoDV-1 is the bicolored white-toothed shrew (Crocidura leucodon) within the order Insectivora. So far, it is unknown if there are other reservoir species for BoDV-1. Bicolored white-tailed shrews remain infected livelong without developing disease. The virus can be excreted via urine, feces, and saliva. So far, occurrence of the virus is limited to certain regions in Eastern and Southern Germany, Switzerland, and Liechtenstein.
Other mammals, in particular horses and sheep, but also humans can act as dead end hosts of BoDV-1. Here the virus can lead to infections of the brain and to severe, often fatal encephalitis. According to the current knowledge, dead end hosts do not excrete the virus. Only minimum amounts, if at all, can be detected in the blood. Natural transmission of the virus from infected horses, sheep or humans to other mammals has not been observed so far.
In the 1990s, the role of BoDV-1 in the development of psychiatric diseases in humans was discussed controversially. However this hypothesis could not be proven scientifically. Recent investigations first confirmed the occurrence of BoDV-1 disease (acute encephalitis) in humans.
Variegated squirrel bornavirus 1, VSBV-1
VSBV-1, identified in 2015, is genetically related to BoDV-1 and was detected in variegated squirrels and Prevost’s squirrels (Sciurus variegatoides and Callosciurus prevostii); isolated cases were found in other related exotic squirrel species. Rarely, transmission of the virus from infected squirrels to breeders or animal keepers occurred. These infections caused severe and in most cases fatal encephalitis.
Based on the potential danger for humans the FLI recommends to investigate all squirrels kept in captivity for VSBV-1. So far, the virus has not been detected in indigenous wild squirrels. Currently, there is no indication that VSBV-1 occurs in other animal species than squirrels. Further investigations on the identification of other susceptible species and on the origin of the virus are ongoing.