One Health in action: Investigation of the first detected local cluster of fatal borna disease virus 1 (BoDV-1) encephalitis, Germany 2022.

BACKGROUND: Zoonotic Borna disease virus 1 (BoDV-1) causes fatal encephalitis in humans and animals. Subsequent to the detection of two paediatric cases in a Bavarian municipality in Germany within three years, we conducted an interdisciplinary One Health investigation. We aimed to explore seroprevalence in a local human population with a risk for BoDV-1 exposure as well as viral presence in environmental samples from local sites and BoDV-1 prevalence within the local small mammal population and its natural reservoir, the bicoloured white-toothed shrew (Crocidura leucodon). METHODS: The municipality's adult residents participated in an anonymised sero-epidemiological study. 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 were detected in human samples. BoDV-1-RNA was also undetectable in 38 environmental samples and 336 ticks. Of 220 collected shrews, twelve of 40 C. leucodon (30%) tested BoDV-1-RNA-positive. BoDV-1-sequences from the previously diagnosed two paediatric patients belonged to two different subclades, that were also present in shrews from the municipality. INTERPRETATION: Our data support the interpretation that human BoDV-1 infections are rare even in endemic areas and primarily manifest as severe encephalitis. Sequence analysis linked both previous paediatric human infections to the local shrew population, but indicated independent infection sources. FUNDING: The project was partly financed by funds of the German Federal Ministry of Education and Research (grant numbers: 01KI2005A, 01KI2005C, 01KI1722A, 01KI1722C, 01KI2002 to MaBe, DR, RGU, DT, BS) as well as by the ReForM-A programme of the University Hospital Regensburg (to MaBa) and by funds of the Bavarian State Ministry of Health, Care and Prevention, project "Zoonotic Bornavirus Focal Point Bavaria - ZooBoFo" (to MaBa, MaBe, BS, MMB, DR, PS, RGU).

Detection of hepatitis E virus genotype 3 in an Algerian mouse (Mus spretus) in Portugal.

Virus monitoring in small mammals is central to the design of epidemiological control strategies for rodent-borne zoonotic viruses. Synanthropic small mammals are versatile and may be potential carriers of several microbial agents. In the present work, a total of 330 fecal samples of small mammals were collected at two sites in the North of Portugal and screened for zoonotic hepatitis E virus (HEV, species Paslahepevirus balayani). Synanthropic small mammal samples (n = 40) were collected in a city park of Porto and belonged to the species Algerian mouse (Mus spretus) (n = 26) and to the greater white-toothed shrew (Crocidura russula) (n = 14). Furthermore, additional samples were collected in the Northeast region of Portugal and included Algerian mouse (n = 48), greater white-toothed shrew (n = 47), wood mouse (Apodemus sylvaticus) (n = 43), southwestern water vole (Arvicola sapidus) (n = 52), Cabrera's vole (Microtus cabrerae) (n = 49) and Lusitanian pine vole (Microtus lusitanicus) (n = 51). A nested RT-PCR targeting a part of open reading frame (ORF) 2 region of the HEV genome was used followed by sequencing and phylogenetic analysis. HEV RNA was detected in one fecal sample (0.3%; 95% confidence interval, CI: 0.01-1.68) from a synanthropic Algerian mouse that was genotyped as HEV-3, subgenotype 3e. This is the first study reporting the detection of HEV-3 in a synanthropic rodent, the Algerian mouse. The identified HEV isolate is probably the outcome of either a spill-over infection from domestic pigs or wild boars, or the result of passive viral transit through the intestinal tract. This finding reinforces the importance in the surveillance of novel potential hosts for HEV with a particular emphasis on synanthropic animals.

Lymphocytic Choriomeningitis Virus Lineage V in Wood Mice, Germany.

We identified a novel lineage of lymphocytic choriomeningitis virus, tentatively named lineage V, in wood mice (Apodemus sylvaticus) from Germany. Wood mouse-derived lymphocytic choriomeningitis virus can be found across a substantially greater range than previously thought. Increased surveillance is needed to determine its geographic range and zoonotic potential.

Small mammal community composition impacts bank vole (Clethrionomys glareolus) population dynamics and associated seroprevalence of Puumala orthohantavirus.

Rodents are important reservoirs for zoonotic pathogens that cause diseases in humans. Biodiversity is hypothesized to be closely related to pathogen prevalence through multiple direct and indirect pathways. For example, the presence of non-host species can reduce contact rates of the main reservoir host and thus reduce the risk of transmission ("dilution effect"). In addition, an overlap in ecological niches between two species could lead to increased interspecific competition, potentially limiting host densities and reducing density-dependent pathogen transmission processes. In this study, we investigated the relative impact of population-level regulation of direct and indirect drivers of the prevalence of Puumala orthohantavirus (PUUV) in bank voles (Clethrionomys glareolus) during years with high abundance. We compiled data on small mammal community composition from four regions in Germany between 2010 and 2013. Structural equation modeling revealed a strong seasonality in PUUV control mechanisms in bank voles. The abundance of shrews tended to have a negative relationship with host abundance, and host abundance positively influenced PUUV seroprevalence, while at the same time increasing the abundance of competing non-hosts like the wood mouse (Apodemus sylvaticus) and the yellow-necked field mouse (Apodemus flavicollis) were associated with reduced PUUV seroprevalence in the host. These results indicate that for PUUV in bank voles, dilution is associated with increased interspecific competition. Anthropogenic pressures leading to the decline of Apodemus spp. in a specific habitat could lead to the amplification of mechanisms promoting PUUV transmission within the host populations.

Rat hepatitis E virus (Rocahepevirus ratti) in people living with HIV.

Rat hepatitis E virus (ratHEV; species Rocahepevirus ratti) is considered a newly emerging cause of acute hepatitis of zoonotic origin. ratHEV infection of people living with HIV (PLWH) might portend a worse, as with hepatitis E virus (HEV; species Paslahepevirus balayani), and consequently this group may constitute a high-risk population. We aimed to evaluate the prevalence of ratHEV by measuring viral RNA and specific IgG antibodies in a large Spanish cohort of PLWH. Multicentre study conducted in Spain evaluating PLWHIV included in the Spanish AIDS Research Network (CoRIS). Patients were evaluated for ratHEV infection using PCR at baseline and anti-ratHEV IgG by dot blot analysis to evaluate exposure to ratHEV strains. Patients with detectable ratHEV RNA were followed-up to evaluate persistence of viremia and IgG seroconversion. Eight-hundred and forty-two individuals were tested. A total of 9 individuals showed specific IgG antibodies against ratHEV, supposing a prevalence of 1.1 (95% CI; 0.5%-2.1%). Of these, only one was reactive to HEV IgG antibodies by ELISA. One sample was positive for ratHEV RNA (prevalence of infection: 0.1%; 95% CI: 0.08%-0.7%). The case was a man who had sex with men exhibiting a slightly increased alanine transaminase level (49 IU/L) as only biochemical alteration. In the follow-up, the patients showed undetectable ratHEV RNA and seroconversion to specific ratHEV IgG antibodies. Our study shows that ratHEV is geographical broadly distributed in Spain, representing a potential zoonotic threat.

Hantavirus Disease Cluster Caused by Seoul Virus, Germany.

A cluster of 3 persons in Germany experienced hantavirus disease with renal insufficiency. Reverse transcription PCR-based genotyping revealed infection by Seoul hantavirus transmitted from pet rats. Seoul virus could be responsible for disease clusters in Europe, and infected pet rats should be considered a health threat.

Case report: tularaemia in a white-handed gibbon (Hylobates lar), Germany.

In 2021, a white-handed gibbon (Hylobates lar) succumbed to illness shortly after transfer from one zoo to another in Germany, due to Francisella tularensis subsp. holarctica infection. To determine the source of infection, whole genome sequencing of the gibbon-derived isolate was performed and wild pest rodents (and captive squirrels) from both zoos were screened for F. tularensis. The F. tularensis whole genome sequence obtained from the gibbon was closely related to previous subclade B.281 sequences obtained from hares from Baden-Wuerttemberg, the same region where the gibbon was first housed. However, F. tularensis DNA was detected in one Norway rat from the receiving zoo. Therefore, neither zoo can be excluded as the source of infection.

Continuous presence of genetically diverse rustrela virus lineages in yellow-necked field mouse reservoir populations in northeastern Germany.

Rustrela virus (RusV; species Rubivirus strelense, family Matonaviridae) was discovered in different zoo animal species affected by fatal encephalitis. Simultaneous RusV RNA detection in multiple yellow-necked field mice (Apodemus flavicollis) suggested this rodent as a reservoir of RusV. Here, we investigated 1,264 yellow-necked field mice and sympatric other small mammals from different regions in Germany for RusV RNA using an optimized reverse transcription-quantitative polymerase chain reaction (RT-qPCR) protocol and high-throughput sequencing. The investigation resulted in the detection of RusV RNA exclusively in 50 of 396 (12.6 per cent) yellow-necked field mice but absence in other sympatric species. RT-qPCR-determined tissue distribution of RusV RNA revealed the highest viral loads in the central nervous system, with other tissues being only very rarely affected. The histopathological evaluation did not reveal any hints of encephalitis in the brains of infected animals despite the detection of viral RNA in neurons by in situ hybridization (ISH). The positive association between the body mass of yellow-necked field mice and RusV RNA detection suggests a persistent infection. Phylogenetic analysis of partial E1 and full-genome sequences showed a high diversification with at least four RusV lineages (1A-1D) in northeastern Germany. Moreover, phylogenetic and isolation-by-distance analyses indicated evolutionary processes of RusV mostly in local reservoir populations. A comparison of complete genome sequences from all detected RusV lineages demonstrated a high level of amino acid and nucleotide sequence variability within a part of the p150 peptide of the non-structural polyprotein and its coding sequence, respectively. The location of this region within the RusV genome and its genetic properties were comparable to the hypervariable region of the rubella virus. The broad range of detected RusV spillover hosts in combination with its geographical distribution in northeastern Germany requires the assessment of its zoonotic potential and further analysis of encephalitis cases in mammals. Future studies have to prove a putative co-evolution scenario for RusV in the yellow-necked field mouse reservoir.

Increased rat-borne zoonotic disease hazard in greener urban areas.

Urban greening has benefits for both human and environmental health. However, urban greening might also have negative effects as the abundance of wild rats, which can host and spread a great diversity of zoonotic pathogens, increases with urban greenness. Studies on the effect of urban greening on rat-borne zoonotic pathogens are currently unavailable. Therefore, we investigated how urban greenness is associated with rat-borne zoonotic pathogen prevalence and diversity, and translated this to human disease hazard. We screened 412 wild rats (Rattus norvegicus and Rattus rattus) from three cities in the Netherlands for 18 different zoonotic pathogens: Bartonella spp., Leptospira spp., Borrelia spp., Rickettsia spp., Anaplasma phagocytophilum, Neoehrlichia mikurensis, Spiroplasma spp., Streptobacillus moniliformis, Coxiella burnetii, Salmonella spp., methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase (ESBL)/AmpC-producing Escherichia coli, rat hepatitis E virus (ratHEV), Seoul orthohantavirus, Cowpox virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Toxoplasma gondii and Babesia spp. We modelled the relationships between pathogen prevalence and diversity and urban greenness. We detected 13 different zoonotic pathogens. Rats from greener urban areas had a significantly higher prevalence of Bartonella spp. and Borrelia spp., and a significantly lower prevalence of ESBL/AmpC-producing E. coli and ratHEV. Rat age was positively correlated with pathogen diversity while greenness was not related to pathogen diversity. Additionally, Bartonella spp. occurrence was positively correlated with that of Leptospira spp., Borrelia spp. and Rickettsia spp., and Borrelia spp. occurrence was also positively correlated with that of Rickettsia spp. Our results show an increased rat-borne zoonotic disease hazard in greener urban areas, which for most pathogens was driven by the increase in rat abundance rather than pathogen prevalence. This highlights the importance of keeping rat densities low and investigating the effects of urban greening on the exposure to zoonotic pathogens in order to make informed decisions and to take appropriate countermeasures preventing zoonotic diseases.

Genome analysis of the novel putative rotavirus species K.

Rotaviruses are causative agents of diarrhea in humans and animals. Currently, the species rotavirus A-J (RVA-RVJ) and the putative species RVK and RVL are defined, mainly based on their genome sequence identities. RVK strains were first identified in 2019 in common shrews (Sorex aranaeus) in Germany; however, only short sequence fragments were available so far. Here, we analyzed the complete coding regions of strain RVK/shrew-wt/GER/KS14-0241/2013, which showed highest sequence identities with RVC. The amino acid sequence identity of VP6, which is used for rotavirus species definition, reached only 51% with other rotavirus reference strains thus confirming classification of RVK as a separate species. Phylogenetic analyses for the deduced amino acid sequences of all 11 virus proteins showed, that for most of them RVK and RVC formed a common branch within the RVA-like phylogenetic clade. Only the tree for the highly variable NSP4 showed a different branching; however, with very low bootstrap support. Comparison of partial nucleotide sequences of other RVK strains from common shrews of different regions in Germany indicated a high degree of sequence variability (61-97% identity) within the putative species. These RVK strains clustered separately from RVC genotype reference strains in phylogenetic trees indicating diversification of RVK independent from RVC. The results indicate that RVK represents a novel rotavirus species, which is most closely related to RVC.

Janus kinase-inhibition modulates hepatitis E virus infection.

Hepatitis E virus (HEV) usually causes a self-limiting disease, but especially immunocompromised individuals are at risk to develop a chronic and severe course of infection. Janus kinase (JAK) inhibitors (JAKi) are a novel drug class for the treatment of autoimmune inflammatory rheumatic disease (AIRD). As JAKs play a key role in innate immunity, viral infections and reactivations are frequently reported during JAKi treatment in AIRD patients. The aim of this study was to characterize the influence of JAKis on HEV replication. To this end, we evaluated liver enzymes of an AIRD patient under JAKi therapy with hepatitis E. Further, experiments with HEV (Kernow-C1 p6) were performed by infection of primary human hepatocytes (PHHs) followed by immunofluorescence staining of viral markers and transcriptomic analysis. Infection experiments in PHHs displayed an up to 50-fold increase of progeny virus production during JAKi treatment and transcriptomic analysis revealed induction of antiviral programs during infection. Upregulation of interferon-stimulated genes (ISG) was perturbed in the presence of JAKis, concomitant with elevated HEV RNA levels. The obtained results suggest that therapeutic JAK inhibition increases HEV replication by modulating the HEV-triggered immune response. Therefore, JAKi treatment and the occurrence of elevated liver enzymes requires a monitoring of potential HEV infections.

Spotted Fever Group Rickettsiae in Ticks and Small Mammals from Grassland and Forest Habitats in Central Germany.

Rickettsiae of the spotted fever group (SFG) are zoonotic tick-borne pathogens. Small mammals are important hosts for the immature life stages of two of the most common tick species in Europe, Ixodes ricinus and Dermacentor reticulatus. These hosts and vectors can be found in diverse habitats with different vegetation types like grasslands and forests. To investigate the influence of environmental and individual factors on Rickettsia prevalence, this study aimed to analyse the prevalence of SFG rickettsiae in ticks and small mammals in different small-scale habitats in central Germany for the first time. Small mammals of ten species and ticks of two species were collected from grasslands and forests in the Hainich-Dün region, central Germany. After species identification, DNA samples from 1098 ticks and ear snips of 1167 small mammals were screened for Rickettsia DNA by qPCR targeting the gltA gene. Positive samples were retested by conventional PCR targeting the ompB gene and sequencing. Rickettsia DNA was detected in eight out of ten small mammal species. Small mammal hosts from forests (14.0%) were significantly more often infected than those from grasslands (4.4%) (p < 0.001). The highest prevalence was found in the mostly forest-inhabiting genus Apodemus (14.8%) and the lowest in Microtus (6.6%), which inhabits grasslands. The prevalence was higher in D. reticulatus (46.3%) than in the I. ricinus complex (8.6%). Adult ticks were more often infected than nymphs (p = 0.0199). All sequenced rickettsiae in I. ricinus complex ticks were R. helvetica, and the ones in D. reticulatus were R. raoultii. Unlike adults, questing nymphs have had only one blood meal, which explains the higher prevalence in I. ricinus adults. Interestingly, habitat type did influence infection probability in small mammals, but did not in ticks. A possible explanation may be the high prevalence in Apodemus flavicollis and A. sylvaticus which were more abundant in the forest.

Structural and mechanistic basis of neutralization by a pan-hantavirus protective antibody.

Emerging rodent-borne hantaviruses cause severe diseases in humans with no approved vaccines or therapeutics. We recently isolated a monoclonal broadly neutralizing antibody (nAb) from a Puumala virus-experienced human donor. Here, we report its structure bound to its target, the Gn/Gc glycoprotein heterodimer comprising the viral fusion complex. The structure explains the broad activity of the nAb: It recognizes conserved Gc fusion loop sequences and the main chain of variable Gn sequences, thereby straddling the Gn/Gc heterodimer and locking it in its prefusion conformation. We show that the nAb's accelerated dissociation from the divergent Andes virus Gn/Gc at endosomal acidic pH limits its potency against this highly lethal virus and correct this liability by engineering an optimized variant that sets a benchmark as a candidate pan-hantavirus therapeutic.

White-Toothed Shrews (Genus Crocidura): Potential Reservoirs for Zoonotic Leptospira spp. and Arthropod-Borne Pathogens?

Three species of white-toothed shrews of the order Eulipotyphla are present in central Europe: the bicolored (Crocidura leucodon), greater (Crocidura russula) and lesser (Crocidura suaveolens) white-toothed shrews. Their precise distribution in Germany is ill-defined and little is known about them as reservoirs for zoonotic pathogens (Leptospira spp., Coxiella burnetii, Brucella spp., Anaplasma phagocytophilum, Babesia spp., Neoehrlichia mikurensis and Bartonella spp.). We investigated 372 Crocidura spp. from Germany (n = 341), Austria (n = 18), Luxembourg (n = 2) and Slovakia (n = 11). West European hedgehogs (Erinaceus europaeus) were added to compare the presence of pathogens in co-occurring insectivores. Crocidura russula were distributed mainly in western and C. suaveolens mainly in north-eastern Germany. Crocidura leucodon occurred in overlapping ranges with the other shrews. Leptospira spp. DNA was detected in 28/227 C. russula and 2/78 C. leucodon samples. Further characterization revealed that Leptospira kirschneri had a sequence type (ST) 100. Neoehrlichia mikurensis DNA was detected in spleen tissue from 2/213 C. russula samples. Hedgehogs carried DNA from L. kirschneri (ST 100), L. interrogans (ST 24), A. phagocytophilum and two Bartonella species. This study improves the knowledge of the current distribution of Crocidura shrews and identifies C. russula as carrier of Leptospira kirschneri. However, shrews seem to play little-to-no role in the circulation of the arthropod-borne pathogens investigated.

[Viral zoonoses in Germany: a One Health perspective]. / Virale Zoonosen in Deutschland aus der One Health-Perspektive.

The COVID-19 pandemic and the increasing occurrence of monkeypox (mpox) diseases outside Africa have illustrated the vulnerability of populations to zoonotic pathogens. In addition, other viral zoonotic pathogens have gained importance in recent years.This review article addresses six notifiable viral zoonotic pathogens as examples to highlight the need for the One Health approach in order to understand the epidemiology of the diseases and to derive recommendations for action by the public health service. The importance of environmental factors, reservoirs, and vectors is emphasized, the diseases in livestock and wildlife are analyzed, and the occurrence and frequency of diseases in the population are described. The pathogens selected here differ in their reservoirs and the role of vectors for transmission, the impact of infections on farm animals, and the disease patterns observed in humans. In addition to zoonotic pathogens that have been known in Germany for a long time or were introduced recently, pathogens whose zoonotic potential has only lately been shown are also considered.For the pathogens discussed here, there are still large knowledge gaps regarding the transmission routes. Future One Health-based studies must contribute to the further elucidation of their transmission routes and the development of prevention measures. The holistic approach does not necessarily include a focus on viral pathogens/diseases, but also includes the question of the interaction of viral, bacterial, and other pathogens, including antibiotic resistance and host microbiomes.

Impact of climate change on vector- and rodent-borne infectious diseases.

Background: Endemic and imported vector- and rodent-borne infectious agents can be linked to high morbidity and mortality. Therefore, vector- and rodent-borne human diseases and the effects of climate change are important public health issues. Methods: For this review, the relevant literature was identified and evaluated according to the thematic aspects and supplemented with an analysis of surveillance data for Germany. Results: Factors such as increasing temperatures, changing precipitation patterns, and human behaviour may influence the epidemiology of vector- and rodent-borne infectious diseases in Germany. Conclusions: The effects of climatic changes on the spread of vector- and rodent-borne infectious diseases need to be further studied in detail and considered in the context of climate adaptation measures.

Field survey and molecular characterization of apicomplexan parasites in small mammals from military camps in Afghanistan.

Small mammals are an important reservoir for causative agents of numerous infectious diseases, including zoonotic and vector-borne diseases. The occurrence of these pathogens represents a regional but permanent threat for humans and animals in general and might especially weaken military personnel and companion animals in abroad missions. In our study, small mammals collected in military camps in Afghanistan (Feyzabad, Mazar-e Sharif, and Kunduz) were investigated for the presence of apicomplexans using histopathology and molecular methods. For this purpose, well-established and newly developed real-time PCR assays were applied. A high prevalence was detected not only in house mice (Mus musculus), but also in shrews (Crocidura cf. suaveolens) and grey dwarf hamsters (Cricetulus migratorius). The molecular characterization based on the 18S rRNA gene revealed a close relationship to a cluster of Hepatozoon sp. detected in voles of the genus Microtus. Hepatozoon canis DNA was detected in one house mouse as well as in two Rhipicephalus ticks from a dog puppy. In addition, around 5% of the house mice were found to be infected with far related adeleorinids showing the highest sequence identity of 91.5% to Klossiella equi, the only published Klossiella sequence at present. For their better phylogenetic characterization, we conducted metagenomics by sequencing of two selected samples. The resulting 18S rRNA gene sequences have a length of about 2400 base pairs including an insertion of about 500 base pairs and are 100% identical to each other. Histopathology together with organ tropism and detection rates verified this sequence as of Klossiella muris. In conclusion, we documented naturally occurring protozoan stages and the additional taxonomic characterization of a well-known commensal in mice by applying a combination of different approaches. The study is of medical, social, and biological importance for ensuring human and animal health in military camps and also stresses the required awareness for the potential risk of zoonoses.

Tropism of Puumala orthohantavirus and Endoparasite Coinfection in the Bank Vole Reservoir.

In Europe, most cases of human hantavirus disease are caused by Puumala orthohantavirus (PUUV) transmitted by bank voles (Clethrionomys glareolus, syn. Myodes glareolus), in which PUUV causes inconspicuous infection. Little is known about tropism and endoparasite coinfections in PUUV-infected reservoir and spillover-infected rodents. Here, we characterized PUUV tropism, pathological changes and endoparasite coinfections. The voles and some non-reservoir rodents were examined histologically, immunohistochemically, by in situ hybridization, indirect IgG enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction. PUUV RNA and anti-PUUV antibodies were detected simultaneously in a large proportion of the bank voles, indicating persistent infection. Although PUUV RNA was not detected in non-reservoir rodents, the detection of PUUV-reactive antibodies suggests virus contact. No specific gross and histological findings were detected in the infected bank voles. A broad organ tropism of PUUV was observed: kidney and stomach were most frequently infected. Remarkably, PUUV was detected in cells lacking the typical secretory capacity, which may contribute to the maintenance of virus persistence. PUUV-infected wild bank voles were found to be frequently coinfected with Hepatozoon spp. and Sarcocystis (Frenkelia) spp., possibly causing immune modulation that may influence susceptibility to PUUV infection or vice versa. The results are a prerequisite for a deeper understanding of virus-host interactions in natural hantavirus reservoirs.

Mystery of fatal 'staggering disease' unravelled: novel rustrela virus causes severe meningoencephalomyelitis in domestic cats.

'Staggering disease' is a neurological disease entity considered a threat to European domestic cats (Felis catus) for almost five decades. However, its aetiology has remained obscure. Rustrela virus (RusV), a relative of rubella virus, has recently been shown to be associated with encephalitis in a broad range of mammalian hosts. Here, we report the detection of RusV RNA and antigen by metagenomic sequencing, RT-qPCR, in-situ hybridization and immunohistochemistry in brain tissues of 27 out of 29 cats with non-suppurative meningoencephalomyelitis and clinical signs compatible with'staggering disease' from Sweden, Austria, and Germany, but not in non-affected control cats. Screening of possible reservoir hosts in Sweden revealed RusV infection in wood mice (Apodemus sylvaticus). Our work indicates that RusV is the long-sought cause of feline 'staggering disease'. Given its reported broad host spectrum and considerable geographic range, RusV may be the aetiological agent of neuropathologies in further mammals, possibly even including humans.