Borna disease is an infectious neurological syndrome of warm-blooded animals, caused by Borna disease virus, which causes abnormal behaviour and fatality.
The causative agent of Borna disease, Borna disease virus (BDV) is a neurotropic virus and is a member of the Bornaviridae family within the Mononegavirales order. Avian bornaviruses, a group of related viruses, have recently been identified as the cause of Proventricular Dilatation Disease, a disease of pet birds.
Although the Borna disease virus is mainly seen as the causative agent of borna disease in horses and other animals, recent findings have implicated that borna virus may play a role in some human neurological and psychiatric conditions including bipolar disorder and depression.
BDV also infects humans and is therefore considered to be a zoonotic agent. The role of BDV in human illness is controversial and it is yet to be established whether BDV causes any overt disease in humans. However, correlative evidence exists linking BDV infection with neuropsychiatric disorders such as bipolar disorder.