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

Abstract

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.

Search for polyoma-, herpes-, and bornaviruses in squirrels of the family Sciuridae

“…Squirrels (n = 126) of five species belonging to the family Sciuridae were collected in four different countries (Canada, USA, Italy and UK), dissected according to standard protocols and brain, lung and spleen samples of these animals were available for screening for all three viruses. In addition, lung and spleen samples from another 112 squirrels belonging to another three species were available from previous bornavirus studies [17,21,22]. Thus, a total of 361 organ samples (243 spleen samples and 118 lung samples) were available for PyV and HV analyses (Tables 1, 2 and 3).…”

“…Brain samples of the newly dissected 126 squirrels were screened with broad-range and VSBV-1 specific RT-qPCRs (Additional file 1) as described previously [17,28]. The other animals (n = 112) have already been investigated before [17,21,22].…”

“…Recently a novel zoonotic bornavirus, variegated squirrel bornavirus 1 (VSBV-1), was detected in five different squirrel species from private holdings and zoos, including Sciurus variegatoides and Callosciurus prevostii and is associated with cases of fatal encephalitis of their breeders and care takers [17,[21][22][23]. Bornaviruses (family Bornaviridae) are enveloped spherically structured viruses with a single-stranded RNA genome of negative polarity (size around 8.9 kilobases (kb)).…”

Bornavirus

“…Natürliche Infektionen werden bei Spitzmäusen und Hörnchen nachgewiesen, die die Infektion mit Bornavirus tolerieren und persistent Bornavirus ausscheiden. Bisher ist nicht geklärt, auf welchem Wege sich diese Tiere infizieren [45][46][47]. [48].…”

“…Verbreitung von VSBV-1 in Hörnchen in Deutschland, in den Niederlanden, Kroatien und im Vereinigten Königreich wurden etwa 800 Proben von 20 Hörnchenspezies aus fünf verschiedenen Subfamilien untersucht [46,47]. Keines der untersuchten Tiere wies klinische Symptome auf.…”