Detection of virus-specific T cells via ELISpot corroborates early diagnosis in human Borna disease virus 1 (BoDV-1) encephalitis

Within endemic regions in southern and eastern Germany, Borna disease virus 1 (BoDV-1) causes rare zoonotic spill-over infections in humans, leading to encephalitis with a high case-fatality risk. So far, intra-vitam diagnosis has mainly been based on RT-qPCR from cerebrospinal fluid (CSF) and serology, both being associated with diagnostic challenges. A positive ELISpot result from peripheral blood was obtained while virus-specific IgG antibodies were not yet detectable in serum and CSF, potentially due to previous immune adsorption for assumed autoimmune-mediated encephalitis. This case demonstrates that a BoDV-1 ELISpot serves as additional diagnostic tool even when BoDV-1 serology might still be negative.