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

Rustrela Virus in Wild Mountain Lion (Puma concolor) with Staggering Disease, Colorado, USA

We identified a rustrela virus variant in a wild mountain lion (Puma concolor) in Colorado, USA. The animal had clinical signs and histologic lesions compatible with staggering disease. Considering its wide host range in Europe, rustrela virus should be considered as a cause for neurologic diseases among mammal species in North America.

A single-point mutation in the rubella virus E1 glycoprotein promotes rescue of recombinant vesicular stomatitis virus

Rubella virus (RuV) is an enveloped plus-sense RNA virus and a member of the Rubivirus genus. RuV infection in pregnant women can lead to miscarriage or an array of severe birth defects known as congenital rubella syndrome. Novel rubiviruses were recently discovered in various mammals, highlighting the spillover potential of other rubiviruses to humans. Many features of the rubivirus infection cycle remain unexplored. To promote the study of rubivirus biology, here, we generated replication-competent recombinant VSV-RuV (rVSV-RuV) encoding the RuV transmembrane glycoproteins E2 and E1. Sequencing of rVSV-RuV showed that the RuV glycoproteins acquired a single-point mutation W448R in the E1 transmembrane domain. The E1 W448R mutation did not detectably alter the intracellular expression, processing, glycosylation, colocalization, or dimerization of the E2 and E1 glycoproteins. Nonetheless, the mutation enhanced the incorporation of RuV E2/E1 into VSV particles, which bud from the plasma membrane rather than the RuV budding site in the Golgi. Neutralization by E1 antibodies, calcium dependence, and cell tropism were comparable between WT-RuV and either rVSV-RuV or RuV containing the E1 W448R mutation. However, the E1 W448R mutation strongly shifted the threshold for the acid pH-triggered virus fusion reaction, from pH 6.2 for the WT RuV to pH 5.5 for the mutant. These results suggest that the increased resistance of the mutant RuV E1 to acidic pH promotes the ability of viral envelope proteins to generate infectious rVSV and provide insights into the regulation of RuV fusion during virus entry and exit.IMPORTANCERubella virus (RuV) infection in pregnant women can cause miscarriage or severe fetal birth defects. While a highly effective vaccine has been developed, RuV cases are still a significant problem in areas with inadequate vaccine coverage. In addition, related viruses have recently been discovered in mammals, such as bats and mice, leading to concerns about potential virus spillover to humans. To facilitate studies of RuV biology, here, we generated and characterized a replication-competent vesicular stomatitis virus encoding the RuV glycoproteins (rVSV-RuV). Sequence analysis of rVSV-RuV identified a single-point mutation in the transmembrane region of the E1 glycoprotein. While the overall properties of rVSV-RuV are similar to those of WT-RuV, the mutation caused a marked shift in the pH dependence of virus membrane fusion. Together, our studies of rVSV-RuV and the identified W448R mutation expand our understanding of rubivirus biology and provide new tools for its study.

Five Species of Wild Freshwater Sport Fish in Wisconsin, USA, Reveal Highly Diverse Viromes

Studies of marine fish have revealed distant relatives of viruses important to global fish and animal health, but few such studies exist for freshwater fish. To investigate whether freshwater fish also host such viruses, we characterized the viromes of five wild species of freshwater fish in Wisconsin, USA: bluegill (Lepomis macrochirus), brown trout (Salmo trutta), lake sturgeon (Acipenser fulvescens), northern pike (Esox lucius), and walleye (Sander vitreus). We analyzed 103 blood serum samples collected during a state-wide survey from 2016 to 2020 and used a metagenomic approach for virus detection to identify known and previously uncharacterized virus sequences. We then characterized viruses phylogenetically and quantified prevalence, richness, and relative abundance for each virus. Within these viromes, we identified 19 viruses from 11 viral families: Amnoonviridae, Circoviridae, Coronaviridae, Hepadnaviridae, Peribunyaviridae, Picobirnaviridae, Picornaviridae, Matonaviridae, Narnaviridae, Nudnaviridae, and Spinareoviridae, 17 of which were previously undescribed. Among these viruses was the first fish-associated coronavirus from the Gammacoronavirus genus, which was present in 11/15 (73%) of S. vitreus. These results demonstrate that, similar to marine fish, freshwater fish also harbor diverse relatives of viruses important to the health of fish and other animals, although it currently remains unknown what effect, if any, the viruses we identified may have on fish health.

The path to eradication of rubella

Since 1969, rubella and its harmful effect on fetuses infected in utero can be prevented by rubella vaccine, usually given in combination with measles vaccine. The rubella vaccine is highly protective both in children and in adults including women intending to become pregnant. Owing to the use of combined measles and rubella vaccines, congenital rubella infection has been eliminated from the Western Hemisphere and nearly all of Europe. Such combined vaccination is now being applied throughout the world, posing the possibility of eventual rubella eradication. The existence of viruses of animals related to rubella does not appear to be a barrier to eradication of the human virus. However, persistent rubella virus in infants infected in utero and of immunosuppressed patients with granulomas may pose a problem for eradication. Nevertheless, this review posits that eradication of rubella is now feasible if routine vaccination of infants and surveillance for chronic infection are correctly applied.

Severe Neurologic Disease in a Horse Caused by Tick-Borne Encephalitis Virus, Austria, 2021

As evidenced by sero-epidemiological studies, infections of horses with the tick-borne encephalitis virus (TBEV) occur frequently in TBEV-endemic areas. However, there are only very few reports of clinical cases. A possible underreporting may be due to a variety of diagnostic challenges. In this study, ELISA and neutralization tests were applied to serum samples. Brain tissue samples were investigated for the presence of nucleic acids of TBEV, Equid alphaherpesvirus 1, Borna disease virus 1, West Nile and Usutu viruses, rustrela virus, as well as Eastern, Western, and Venezuelan equine encephalitis viruses with RT-qPCR, RT-PCR, and qPCR, respectively. TBEV-specific amplification products were subjected to Sanger sequencing. In addition, a direct fluorescent antibody test for rabies was performed. Clinical and patho-histological findings are reported. Using specific RT-qPCR and RT-PCR assays, TBEV nucleic acids were demonstrated in brain tissue samples. Sequencing revealed the Western (formerly Central) European subtype of TBEV as the etiological agent. A high titer of TBEV-specific neutralizing antibodies was found in the serum. RNAscope in situ hybridization revealed TBEV RNA confined to neuronal cell bodies and processes. No other pathogens or nucleic acids thereof could be detected. Diagnostic procedures need to be carried out early after the onset of neurological signs to allow for a final etiological diagnosis of acute TBEV infections in horses.

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.

Rustrela Virus-Associated Encephalomyelitis ('Staggering Disease') in Cats from Eastern Austria, 1994-2016

Clinical cases of 'staggering disease', a nonsuppurative encephalomyelitis associated with gait abnormalities in cats, have been documented for decades in Sweden. In Austria, an increased incidence was observed in the 1990s. Only recently, rustrela virus (RusV) was identified as the causative agent of this clinicopathologic disease entity. In this retrospective study, we analyzed a total of 23 brain and spinal cord samples from Austrian cats with the pathohistological diagnosis of nonsuppurative encephalomyelitis and clinical signs consistent with staggering disease from 1994 to 2016 using reverse transcription real-time polymerase chain reaction (RT-qPCR) and in situ hybridization. We were able to detect RusV nucleic acids in seven of the examined samples. Borna disease virus 1 (BoDV-1) could be excluded in all cases via immunohistochemistry and RT-qPCR. This study confirms that RusV has been a relevant etiological agent of nonsuppurative encephalomyelitis of cats in a geographically and temporally limited disease cluster in Austria, mainly in the 1990s. The geographic distribution of the positive samples in this study is consistent with earlier reports on 'staggering disease' in Austria. Further studies are necessary to confirm the reservoir host of 'staggering disease' in Austria, as well as investigations on the disappearance of this disease and its possible zoonotic potential.

[Viral zoonoses in Germany: a One Health perspective]

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.

Rustrela Virus as Putative Cause of Nonsuppurative Meningoencephalitis in Lions

Retrospective investigation of archived tissue samples from 3 lions displaying nonsuppurative meningoencephalitis and vasculitis led to the detection of rustrela virus (RusV). We confirmed RusV antigen and RNA in cortical neurons, axons, astrocytes and Purkinje cells by reverse transcription quantitative PCR, immunohistochemistry, and in situ hybridization.

Potentially Zoonotic Viruses in Wild Rodents, United Arab Emirates, 2019—A Pilot Study

The majority of emerging viral infectious diseases in humans originate from wildlife reservoirs, such as rodents and bats. We investigated a possible reservoir, namely wild gerbils and mice trapped in a desert reserve within the emirate of Dubai, United Arab Emirates (UAE). In total, 52 gerbils and 1 jird (Gerbillinae), 10 house mice (Mus musculus), and 1 Arabian spiny mouse (Acomys dimidiatus) were sampled. Oro-pharyngeal swabs, fecal samples, attached ticks, and organ samples (where available) were screened by (RT-q)PCR for the following viruses: Middle East respiratory syndrome-related coronavirus, Crimean-Congo hemorrhagic fever orthonairovirus, Alkhumra hemorrhagic fever virus, hantaviruses, Lymphocytic choriomeningitis mammarenavirus, Rustrela virus, poxviruses, flaviviruses, and herpesviruses. All of the samples were negative for all investigated viruses, except for herpesviruses: 19 gerbils (35.8%) and 7 house mice (70.0%) were positive. The resulting sequences were only partly identical to sequences in GenBank. Phylogenetic analysis revealed three novel betaherpesviruses and four novel gammaherpesviruses. Interestingly, species identification of the positive gerbils resulted in eight individuals clustering in a separate clade, most closely related to Dipodillus campestris, the North African gerbil, indicating either the expansion of the geographic range of this species, or the existence of a closely related, yet undiscovered species in the UAE. In conclusion, we could not find evidence of persistence or shedding of potentially zoonotic viruses in the investigated rodent cohorts of limited sample size.