Table 1. Case definitions for BoDV-1 or VSBV-1 encephalitis/encephalopathy, Germany, 2018–2020*.

Case definition
Confirmed case of BoDV-1 or VSBV encephalitis/encephalopathy
Encephalitis or encephalopathy
AND detection of BoDV-1 or VSBV-1 RNA in CSF or CNS tissue
OR detection of BoDV-1 or VSBV-1 antigen by IHC with virus-specific monoclonal antibodies in CNS tissue
Confirmed case of unspecified bornavirus encephalitis/ encephalopathy
Encephalitis or encephalopathy
AND detection of bornavirus antigen by IHC with cross- reactive monoclonal antibodies or polyclonal serum in CNS tissue
Probable case of BoDV-1 or VSBV-1 encephalitis/ encephalopathy
Encephalitis or encephalopathy
AND detection of bornavirus-reactive IgG in a serum or CSF sample by screening test (with full virus antigen, e.g., IFAT) and suitable confirmation assay detecting antibodies against individual bornavirus antigens (derived from infected cells or recombinant antigens, e.g., Western blot, immunoblot, or ELISA)
AND suitable comparative antibody quantification assay able to distinguish antibodies specific for BoDV-1, VSBV-1 or other orthobornaviruses (e.g., IFAT, immunoblot, ELISA)
OR exposure to VSBV-1-positive squirrels or epidemiologic link to BoDV-1-endemic regions
AND no evidence of other reasons for the clinical picture
Probable case of unspecified bornavirus encephalitis/ encephalopathy
Encephalitis or encephalopathy
AND detection of bornavirus-reactive IgG in a serum or CSF sample by screening test (with full virus antigen, e.g., IFAT) and suitable confirmation assay detecting antibodies against individual bornavirus antigens (derived from infected cells or recombinant antigens, e.g., Western blot, immunoblot, or ELISA)
AND detection of bornavirus-reactive IgG in a serum or CSF sample by screening test (with full virus antigen, e.g., IFAT) and suitable confirmation assay detecting antibodies against individual bornavirus antigens (derived from infected cells or recombinant antigens, e.g., Western blot, immunoblot, or ELISA)
Possible case of BoDV-1 or VSBV-1 encephalitis/encephalopathy
Encephalitis or encephalopathy
AND residence in BoDV-1-endemic area or exposure to VSBV-1–positive squirrels
AND no evidence of other reasons for the clinical picture

*Case definitions replace those of Tappe et al. (6). Encephalitis or encephalopathy was defined according to Venkatesan et al. (14). BoDV-1, Borna disease virus 1; CNS, central nervous system; CSF, cerebrospinal fluid; IFAT, immunofluorescence antibody test; IHC, immunohistochemical analysis; VSBV-1, variegated squirrel bornavirus 1.