Borna disease virus (BDV) is a nonsegmented, negative-, single-stranded, highly neurotropic RNA virus with noncytolytic replication in the central nervous system. This virus causes neurological and behavioral disturbances primarily in horses and sheep, in addition to a variety of other vertebrate animal species and in laboratory animal models. BDV is now gaining much of the research attention, because the disturbances seen in animals resemble those of neuropsychiatric disorders in humans. These observations raise the possibility that BDV infection may be associated with certain human disorders.

Serological and molecular studies on many samples from human patients with a variety of psychiatric disorders have been performed. Some reported the presence and elevated levels of serum antibodies to BDV. Others reported the presence of BDV-RNAs or BDV-antigens in the peripheral blood samples as well as in autopsied brains. Taken together these data support the possibility of human infection with BDV. On the contrary, others reported the complete absence of such BDV-markers from their samples, supporting the absence of a link between BDV infection and psychiatric disorders as well as excluding it as a human pathogen. Thus, BDV infection in humans is highly controversial. Further investigations are required to answer the question whether BDV is a human pathogen and moreover, to elucidate the possible role, if any, of BDV in the pathogeneses of these disorders.