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

## TL;DR

This study identifies rustrela virus and Borna disease virus 1 as causes of fatal brain inflammation in various mammals, highlighting their potential as emerging pathogens.

## Contribution

The study expands the host range of rustrela virus to include maned wolves and donkeys, and identifies new cases of Borna disease virus 1 and tick-borne encephalitis virus in multiple species.

## Key findings

- Rustrela virus was detected in maned wolves, cats, and a donkey.
- Borna disease virus 1 and tick-borne encephalitis virus were found in horses and dogs.
- Neurons were the primary target cells for all three viruses.

## Abstract

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.

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.

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.

The online version contains supplementary material available at 10.1186/s12917-025-05132-w.