Multiple detection of zoonotic variegated squirrel bornavirus 1 RNA in different squirrel species suggests a possible unknown origin for the virus

The recently discovered variegated squirrel bornavirus 1 (VSBV-1) caused the death of three squirrel breeders in Germany. Subsequent first screening of squirrels with in vivo collected swab samples and a VSBV-1-specific RT-qPCR revealed not only variegated squirrel infections (Sciurus variegatoides), but also Prevost's squirrels (Callosciurus prevostii) as positive for VSBV-1 genome. In this study, 328 squirrels were tested using the established RT-qPCR assays. In 16 individual animals VSBV-1 RNA could be detected; 15 individuals were from small breedings and zoological gardens in Germany, with the remaining individual being from a zoological garden in Croatia. Positive animals belonged to the species C. prevostii, C. finlaysonii, and Tamiops swinhoei within the subfamily Callosciurinae and Sciurus granatensis within the subfamily Sciurinae. Repeated non-invasive oral swab sampling in one holding indicated positive animals months after a first negative result. Besides the oral swabs, VSBV-1 was also detected in fecal (pool) samples allowing the future monitoring of squirrel holdings based on RT-qPCR investigation of such samples. The detection in zoological gardens emphasizes the need for further investigations into the transmission route to humans in order to develop rational public health measures for prevention of transmission. Finally, the detection of several closely related VSBV-1 sequences in squirrels from different subfamilies raises questions as to the origin of the virus.