Spillover infections by rustrela virus, borna disease virus 1 and tick-borne encephalitis virus revealed by retrospective screening of mammalian encephalitis of unknown origin

Abstract

Background: Cross-species transmission of several viral neuropathogens may lead to fatal disease in incidental hosts. The newly discovered rustrela virus (RusV) as well as Borna disease virus 1 (BoDV-1), tick-borne encephalitis virus (TBEV), and highly pathogenic avian influenza virus (HPAIV) of hemagglutinin subtype H5 may cause fatal lymphocytic meningoencephalitis in a broad range of mammalian species after crossing species borders. Here, we tested brain tissue samples from 191 animals representing 19 mammalian species diagnosed with lymphocytic meningoencephalitis from 1989 to 2024 for these four neuropathogens by RT-qPCR. Positive samples were analysed for cell-associated viral RNA or viral antigen by RNA in situ hybridisation or immunohistochemistry, respectively.

Results: For the first time RusV was detected in one out of two tested maned wolves (50%). Further, two out of 50 cats (4.0%) and the only tested donkey were infected. BoDV-1 and TBEV were found in three out of eight horses (37.5%) and one out of 78 dogs (1.3%), respectively. Neurons were the main target cells for all three pathogens. Partial genomic RusV and BoDV-1 sequences matched with the predominant virus types in the study region. Influenza A virus RNA was not detected in any of the samples.

Conclusions: The host range of RusV was extended to Canidae, represented by a fatal case of a maned wolf. Both RusV and BoDV-1 seem to be important pathogens causing lymphocytic meningoencephalitis in other mammalian species and their distribution should be monitored closely.

Keywords: BoDV-1; HPAIV H5; Influenza a virus (IAV); Meningoencephalitis; RusV; TBEV.

Fig. 1

Phylogenetic analysis of RusV and BoDV-1 sequences. A, E: Neighbour-Joining trees were generated for the sequences determined in this study together with the sequences derived from public databases spanning the same sequence stretch (RusV: 409 nucleotides; n = 75; BoDV-1: 1,824 nucleotides, n = 260). A RusV clade 4 sequence (PP025855) from a mountain lion from Colorado, USA or BoDV-2 sequence No/98 (AJ311524) from a horse in Styria, Austria were used for rooting the trees (not shown). Colours represent RusV genotypes 1 A to 3B [50] or BoDV-1 clusters 1 A to 5 [10]. B, F: Subtrees containing the RusV or BoDV-1 sequences generated in this study (depicted in black). The dark blue vertical bar in panel F indicates BoDV-1 subclade 4.BB [10]. C, D: Geographic localization of RusV sequences. Colours represent RusV genotypes, as shown in panel A. Symbols of the four cases reported in this study are indicated by a thicker black line in panel D. AUT: Austria, GER: Germany, SWE: Sweden; BB: Brandenburg, BE: Berlin, BY: Bavaria; MV: Mecklenburg-Western Pomerania, NI: Lower Saxony, SH: Schleswig-Holstein, ST: Saxony Anhalt, TH: Thuringia.

Fig. 2

Inflammation and cellular localization of RusV, BoDV-1 and TBEV. A-C: Histopathology of the infected brains with perivascular cuffing, marked (A and B) and moderate (haematoxylin and eosin stain). D-F: Representative cellular localization via RNA in situ hybridization for RusV or immunohistochemistry for BoDv-1 and TBEV in neurons D: fast red as chromogenic labelling, E and F: 3,3′-Diaminobenzidin (DAB) for chromogenic labelling, all: Mayer’s haematoxylin counter stain). Bars represent 40 μm.