Epidemiology and host spectrum of Borna disease virus infections

Borna disease virus (BDV) has gained lot of interest because of its zoonotic potential, ability to introduce cDNA of its RNA transcripts into host genomes, and ability to cause severe neurobehavioural diseases. Classical Borna disease is a progressive meningoencephalomyelitis in horses and sheep, known in central Europe for centuries. According to current knowledge, BDV or a close relative also infects several other species, including humans at least occasionally, in central Europe and elsewhere, but the existence of potential 'human Borna disease' with its suspected neuropsychiatric symptoms is highly controversial. The recent detection of endogenized BDV-like genes in primate and various other vertebrate genomes confirms that at least ancient bornaviruses did infect our ancestors. The epidemiology of BDV is largely unknown, but accumulating evidence indicates vectors and reservoirs among small wild mammals. The aim of this review is to bring together the current knowledge on epidemiology of BDV infections. Specifically, geographical and host distribution are addressed and assessed in the critical light of the detection methods used. We also review some salient clinical aspects.