Experimental and natural borna disease virus infections: presence of viral RNA in cells of the peripheral blood.

Cells of the peripheral blood of experimentally and naturally borna disease virus (BDV)-infected animals and of human psychiatric patients and healthy individuals were analyzed for the presence of viral RNA using a BDV-p40-specific nested reverse transcription-polymerase chain reaction (RT-PCR). The assay proved to be highly sensitive as 10 RNA molecules were reproducibly amplified. BDV RNA was detected in blood cells of experimentally infected immunocompetent mice and rats. Mice were persistently infected without showing clinical signs of borna disease (BD), whereas the rats suffered from acute BD. Among 19 horses examined, five were positive for viral RNA in the blood. In a flock of sheep with a history of BD, 1 out of 25 clinically healthy animals was positive. BDV RNA was also detected in cells of the peripheral blood of 10 out of 27 selected humans with psychiatric disorders, and in 2 out of 13 healthy individuals. Remarkably, BDV-specific RNA was present in some cases in the absence of BDV-specific antibodies. Sequence analysis of PCR products confirmed the specificity of the amplification system. The presence of BDV RNA in the blood of naturally and experimentally BDV-infected individuals may point to an incidental but relevant role of blood for the spread of BDV in the infected organism, as well as for the transmission of BDV to other individuals.