One Health in Action: Investigation of the First Detected Local Cluster of Fatal Borna Disease Virus 1 (BoDV-1) Encephalitis, Germany 2022 : [Preprint]

Background: Zoonotic Borna disease virus 1 (BoDV-1) causes fatal encephalitis in humans and animals. Subsequent to the first ever detected local cluster of two paediatric cases in a municipality in Bavaria, Germany, we implemented an interdisciplinary One Health investigation to explore possible transmission routes from its natural reservoir, the bicolored white-toothed shrew (Crocidura leucodon). Furthermore, we aimed to examine the clinical spectrum of human BoDV-1 infections.

Methods: The municipality’s adult residents participated in an anonymised sero-epidemiological study where serum samples were examined for BoDV-1-reactive antibodies, and nasal swabs tested for BoDV‑1-RNA. Potential risk factors and clinical symptoms were assessed by an electronic questionnaire. Small mammals, environmental samples and ticks from the municipality were tested for BoDV-1-RNA. Shrew-derived BoDV‑1-sequences together with sequences of the two human cases were phylogenetically analysed.

Results: In total, 679 citizens participated (response: 41%), of whom 38% reported shrews in their living environment and 19% direct shrew contact. No anti-BoDV-1 antibodies nor BoDV‑1-RNA were detected in the human samples. BoDV-1-RNA was also undetectable in 38 environmental samples and 336 ticks. Of 177 collected shrews, nine of 21 C. leucodon (43%) tested BoDV-1-RNA-positive. BoDV-1-sequences from the human patients belonged to two different subclades, that were also present in shrews from the municipality.

Interpretation: Despite a high probability of shrew contact and confirmed BoDV-1-presence in shrews, no oligo-/asymptomatic or additional clinically manifest human BoDV-1-infections were detected. Sequence analysis linked both human infections to the local shrew population, but indicated independent infection sources.