Severe bornavirus-encephalitis presenting as Guillain-Barré-syndrome

Analysis of BoDV-1 status, EEG resting-state alpha activity and pro-inflammatory cytokines in adults with and without major depressive disorder

Introduction

In severe cases, an infection with the Borna Disease Virus 1 (BoDV-1), the causative agent of Borna disease in horses, sheep, and other domestic mammals, was reported to be accompanied by cognitive dysfunctions, seizures, deep coma, or severe to fatal encephalitis in humans. In addition, asymptomatic or mild courses of BoDV-1 infection are discussed to act as a co-factor in the etiology of Major Depressive Disorder (MDD). Previously, studies using electroencephalography (EEG) reported BoDV-1-dependent changes in event-related potentials (ERPs), thus indicating the use and added value of non-invasive studies in Borna research.

Methods

Here, we examined possible connections between BoDV-1 status, EEG restingstate alpha activity, and serum levels of pro-inflammatory Interleukin 6 (IL-6) and Interleukin 8 (IL-8) in MDD patients and in a comparison group of adults without MDD diagnosis.

Results

Interestingly, for both groups, we revealed a comparable high number of BoDV-1 positive and BoDV-1 negative participants. Compared to adults without MDD diagnosis, MDD patients showed a decrease in their relative EEG alpha power at posterio-central, but increased values at anterio-central electrode sites. Most important, no group-dependent effect of BoDV-1 status on EEG resting-state activity had been observed. Compared to BoDV-1 positive and negative adults without MDD diagnosis, as well as BoDV-1 positive MDD patients, BoDV-1 negative MDD patients revealed a comparatively weak significant negative correlation between relative fronto-central EEG alpha power and concentrations of pro-inflammatory IL-8.

Discussion

Taken together, our data confirm MDD-dependent alterations in EEG resting-state alpha activity, which, however, were not accompanied by major BoDV-1 dependent neurophysiological or immunological effects. Future - probably more invasive - studies further have to clarify the significance of the observed negative correlation between relative fronto-central EEG alpha power and concentrations of pro-inflammatory IL-8.

Long-term Elevation of Complement Factors in Cerebrospinal Fluid of Patients With Borna Disease Virus 1 Encephalitis

BACKGROUND

Borna disease virus 1 (BoDV-1) causes rare but severe zoonotic infections in humans, presenting as encephalitis. The case-fatality risk is very high and no effective countermeasures have been established so far. An immunopathology is presumed, while data on immune responses in humans are limited. Evidence of a role of the complement system in various neurological disorders and in viral infections of the central nervous system is increasing and specific inhibitors are available as therapeutic options.

METHODS

In this study, we investigated factors of the complement system in the cerebrospinal fluid (CSF) of patients with BoDV-1 infections (n = 17) in comparison to noninflammatory control CSF samples (n = 11), using a bead-based multiplex assay. In addition, immunohistochemistry was performed using postmortem brain tissue samples.

RESULTS

We found an intrathecal elevation of complement factors of all complement pathways and an active cascade during human BoDV-1 infections. The increase of certain complement factors such as C1q was persistent, and C3 complement deposits were detected in postmortem brain sections. Intrathecal complement levels were negatively correlated with survival.

CONCLUSIONS

Further investigations are warranted to clarify whether targeting the complement cascade by specific inhibitors might be beneficial for patients suffering from severe BoDV-1 encephalitis.

Detection of virus-specific T cells via ELISpot corroborates early diagnosis in human Borna disease virus 1 (BoDV-1) encephalitis

BACKGROUND

Within endemic regions in southern and eastern Germany, Borna disease virus 1 (BoDV-1) causes rare zoonotic spill-over infections in humans, leading to encephalitis with a high case-fatality risk. So far, intra-vitam diagnosis has mainly been based on RT-qPCR from cerebrospinal fluid (CSF) and serology, both being associated with diagnostic challenges. Whilst low RNA copy numbers in CSF limit the sensitivity of RT-qPCR from this material, seroconversion often occurs late during the course of the disease.

CASE PRESENTATION

Here, we report the new case of a 40 - 50 year-old patient in whom the detection of virus-specific T cells via ELISpot corroborated the diagnosis of BoDV-1 infection. The patient showed a typical course of the disease with prodromal symptoms like fever and headaches 2.5 weeks prior to hospital admission, required mechanical ventilation from day three after hospitalisation and remained in deep coma until death ten days after admission.

RESULTS

Infection was first detected by positive RT-qPCR from a CSF sample drawn four days after admission (viral load 890 copies/mL). A positive ELISpot result was obtained from peripheral blood collected on day seven, when virus-specific IgG antibodies were not detectable in serum, possibly due to previous immune adsorption for suspected autoimmune-mediated encephalitis.

CONCLUSION

This case demonstrates that BoDV-1 ELISpot serves as additional diagnostic tool even in the first week after hospitalisation of patients with BoDV-1 encephalitis.

Lethal Borna disease virus 1 infections of humans and animals - in-depth molecular epidemiology and phylogeography

Borna disease virus 1 (BoDV-1) is the causative agent of Borna disease, a fatal neurologic disorder of domestic mammals and humans, resulting from spill-over infection from its natural reservoir host, the bicolored white-toothed shrew (Crocidura leucodon). The known BoDV-1-endemic area is remarkably restricted to parts of Germany, Austria, Switzerland and Liechtenstein. To gain comprehensive data on its occurrence, we analysed diagnostic material from suspected BoDV-1-induced encephalitis cases based on clinical and/or histopathological diagnosis. BoDV-1 infection was confirmed by RT-qPCR in 207 domestic mammals, 28 humans and seven wild shrews. Thereby, this study markedly raises the number of published laboratory-confirmed human BoDV-1 infections and provides a first comprehensive summary. Generation of 136 new BoDV-1 genome sequences from animals and humans facilitated an in-depth phylogeographic analysis, allowing for the definition of risk areas for zoonotic BoDV-1 transmission and facilitating the assessment of geographical infection sources. Consistent with the low mobility of its reservoir host, BoDV-1 sequences showed a remarkable geographic association, with individual phylogenetic clades occupying distinct areas. The closest genetic relatives of most human-derived BoDV-1 sequences were located at distances of less than 40 km, indicating that spill-over transmission from the natural reservoir usually occurs in the patient´s home region.

Clinical analysis of Bornavirus Encephalitis cases demonstrates a small time window for Etiological Diagnostics and treatment attempts, a large case series from Germany 1996-2022

PURPOSE

The emerging zoonotic Borna disease virus 1 (BoDV-1) and the variegated squirrel bornavirus 1 (VSBV-1) cause severe and fatal human encephalitis in Germany. We conducted the first systematic clinical analysis of acute, molecularly confirmed fatal bornavirus encephalitis cases comprising 21 BoDV-1 and four VSBV-1 patients to identify options for better diagnosis and timely treatment.

METHODS

Analyses were based on medical records and, for BoDV-1, on additional medical interviews with patients' relatives.

RESULTS

Disease onset was unspecific, often with fever and headache, inconsistently mixed with early fluctuating neurological symptoms, all rapidly leading to severe encephalopathy and progressive vigilance decline. Very shortly after seeking the first medical advice (median time interval 2 and 0 days for BoDV-1 and VSBV-1, respectively), all except one patient were hospitalised upon manifest neurological symptoms (median 10 and 16 days respectively after general symptom onset). Neurological symptoms varied, always progressing to coma and death. BoDV-1 and VSBV-1 patients required ventilation a median of three and five days, and died a median of 32 and 72 days, after hospitalisation. Death occurred mostly after supportive treatment cessation at different points in time based on poor prognosis. Disease duration therefore showed a wide, incomparable range.

CONCLUSION

The extremely rapid progression is the most obvious clinical characteristic of bornavirus encephalitis and the timeframe for diagnosis and targeted therapy is very short. Therefore, our results demand an early clinical suspicion based on symptomatology, epidemiology, imaging, and laboratory findings, followed by prompt virological testing as a prerequisite for any potentially effective treatment.

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).

Borna disease in an adult free-ranging Eurasian beaver (Castor fiber albicus)

Borna disease (BD) associated with a peracute bacterial septicaemia with Escherichia coli was diagnosed in an adult female, naturally infected, free-ranging Eurasian beaver of the subspecies Castor fiber albicus, clinically characterized by weight loss, depression, weakness and gurgled peristaltic sounds. The beaver was euthanized humanely. Necropsy and light microscopy revealed a non-purulent meningoencephalitis with typical mononuclear perivascular cuffs and parenchymal infiltrates. The diagnosis of BD was confirmed by detection of viral antigen and RNA by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). The PCR product was sequenced and cluster analysis revealed a close relationship between endemic clusters in Saxony-Anhalt. This is the first report of naturally occurring BD in a free-ranging Eurasian beaver.

No evidence of an association of multiple sclerosis (MS) with Borna disease virus 1 (BoDV-1) infections in patients within an endemic region: a retrospective pilot study

BACKGROUND

Borna disease virus 1 (BoDV-1) causes rare human infections within endemic regions in southern and eastern Germany. The infections reported to date have been linked to severe courses of encephalitis with high mortality and mostly irreversible symptoms. Whether BoDV-1 could act as a trigger for other neurological conditions, is, however, incompletely understood.

OBJECTIVES AND METHODS

In this study, we addressed the question of whether the presentation of a clinically isolated syndrome (CIS) or of multiple sclerosis (MS) might be associated with a milder course of BoDV-1 infections. Serum samples of 100 patients with CIS or MS diagnosed at a tertiary neurological care center within an endemic region in southern Germany and of 50 control patients suffering from headache were retrospectively tested for BoDV-1 infections.

RESULTS

In none of the tested sera, confirmed positive results of anti-BoDV-1-IgG antibodies were retrieved. Our results support the conclusion that human BoDV-1 infections primarily lead to severe encephalitis with high mortality.

Case report: Fatal Borna virus encephalitis manifesting with basal brain and brainstem symptoms

Background

Since the first report of fatal Borna virus-1 (BoDV-1) encephalitis in 2018, cases gradually increased. There is a lack of diagnostic algorithm, and there is no effective treatment so far.

Case presentation

We report an acute BoDV-1 encephalitis in a 77-year-old female with flu-like onset, rapid progression to word-finding difficulties, personality changes, global disorientation, diffuse cognitive slowness, and gait ataxia and further deterioration with fever, meningism, severe hyponatremia, epileptic seizures, cognitive decline, and focal cortical and cerebellar symptoms/signs. The extensive diagnostic workup (cerebrovascular fluid, serum, and MRI) for (meningo-)encephalitis was negative for known causes. Our empirical common antiviral, antimicrobial, and immunosuppressive treatment efforts failed. The patient fell into coma 5 days after admission, lost all brainstem reflexes on day 18, remained fully dependent on invasive mechanical ventilation thereafter and died on day 42. Brain and spinal cord autopsy confirmed an extensive, diffuse, and severe non-purulent, lymphocytic sclerosing panencephalomyelitis due to BoDV-1, affecting neocortical, subcortical, cerebellar, neurohypophysis, and spinal cord areas. Along with our case, we critically reviewed all reported BoDV-1 encephalitis cases.

Conclusion

The diagnosis of acute BoDV-1 encephalitis is challenging and delayed, while it progresses to fatal. In this study, we list all tried and failed treatments so far for future reference and propose a diagnostic algorithm for prompt suspicion and diagnosis.

Borna disease virus 1 infection in alpacas: Comparison of pathological lesions and viral distribution to other dead-end hosts

Borna disease is a progressive meningoencephalitis caused by spillover of the Borna disease virus 1 (BoDV-1) to horses and sheep and has gained attention due to its zoonotic potential. New World camelids are also highly susceptible to the disease; however, a comprehensive description of the pathological lesions and viral distribution is lacking for these hosts. Here, the authors describe the distribution and severity of inflammatory lesions in alpacas (n = 6) naturally affected by this disease in comparison to horses (n = 8) as known spillover hosts. In addition, the tissue and cellular distribution of the BoDV-1 was determined via immunohistochemistry and immunofluorescence. A predominant lymphocytic meningoencephalitis was diagnosed in all animals with differences regarding the severity of lesions. Alpacas and horses with a shorter disease duration showed more prominent lesions in the cerebrum and at the transition of the nervous to the glandular part of the pituitary gland, as compared to animals with longer disease progression. In both species, viral antigen was almost exclusively restricted to cells of the central and peripheral nervous systems, with the notable exception of virus-infected glandular cells of the Pars intermedia of the pituitary gland. Alpacas likely represent dead-end hosts similar to horses and other spillover hosts of BoDV-1.

Magnetic resonance imaging of human variegated squirrel bornavirus 1 (VSBV-1) encephalitis reveals diagnostic pattern indistinguishable from Borna disease virus 1 (BoDV-1) encephalitis but typical for bornaviruses

Human bornavirus encephalitis is an emerging disease caused by the variegated squirrel bornavirus 1 (VSBV-1) and the Borna disease virus 1 (BoDV-1). While characteristic brain magnetic resonance imaging (MRI) changes have been described for BoDV-1 encephalitis, only scarce diagnostic data in VSBV-1 encephalitis exist. We systematically analysed brain MRI scans from all known VSBV-1 encephalitis patients. Initial and follow-up scans demonstrated characteristic T2 hyperintense lesions in the limbic system and the basal ganglia, followed by the brainstem. No involvement of the cerebellar cortex was seen. Deep white matter affection occurred in a later stage of the disease. Strict symmetry of pathologic changes was seen in 62%. T2 hyperintense areas were often associated with low T1 signal intensity and with mass effect. Sinusitis in three patients on the first MRI and an early involvement of the limbic system suggest an olfactory route of VSBV-1 entry. The viral spread could occur per continuitatem to adjacent anatomical brain regions or along specific neural tracts to more distant brain regions. The number and extent of lesions did not correlate with the length of patients' survivals. The overall pattern closely resembles that described for BoDV-1 encephalitis. The exact bornavirus species can thus not be deduced from imaging results alone, and molecular testing and serology should be performed to confirm the causative bornavirus. As VSBV-1 is likely of tropical origin, and MRI investigations are increasingly available globally, imaging techniques might be helpful to facilitate an early presumptive diagnosis of VSBV-1 encephalitis when molecular and/or serological testing is not available.

Risk factors for Borna disease virus 1 encephalitis in Germany - a case-control study

In 2018, Borna Disease Virus 1 (BoDV-1) was confirmed as a human zoonotic pathogen causing rare but fatal encephalitis in Germany. While diagnostic procedures and the clinical picture have been described, epidemiology remains mysterious. Though endemic areas and a natural reservoir host have been identified with the shrew Crocidura leucodon shedding virus in secretions, transmission events, routes and risk factors are unclear. We performed the first comprehensive epidemiological study, combining a large case series with the first case-control study: We interviewed family members of 20 PCR-confirmed BoDV-1 encephalitis cases deceased in 1996-2021 with a standardized questionnaire covering medical history, housing environment, profession, animal contacts, outdoor activities, travel, and nutrition. Cases' median age was 51 (range 11-79) years, 12/20 were female, and 18/20 lived in the federal state of Bavaria in Southeastern Germany. None had a known relevant pre-existing medical condition. None of the interviews yielded a transmission event such as direct shrew contact, but peridomestic shrew presence was confirmed in 13 cases supporting environmental transmission. Residency in rural areas endemic for animal BoDV-1 was the common denominator of all cases. A subsequent individually matched case-control study revealed residence close to nature in a stand-alone location or on the fringe of the settlement as a risk factor for disease in multivariable analysis with an adjusted OR of 10.8 (95% CI 1.3-89.0). Other variables including keeping cats were not associated with disease. Targeted prevention, future post-exposure-prophylaxis, and timely diagnosis remain challenging.

Interactions of Equine Viruses with the Host Kinase Machinery and Implications for One Health and Human Disease

Zoonotic pathogens that are vector-transmitted have and continue to contribute to several emerging infections globally. In recent years, spillover events of such zoonotic pathogens have increased in frequency as a result of direct contact with livestock, wildlife, and urbanization, forcing animals from their natural habitats. Equines serve as reservoir hosts for vector-transmitted zoonotic viruses that are also capable of infecting humans and causing disease. From a One Health perspective, equine viruses, therefore, pose major concerns for periodic outbreaks globally. Several equine viruses have spread out of their indigenous regions, such as West Nile virus (WNV) and equine encephalitis viruses (EEVs), making them of paramount concern to public health. Viruses have evolved many mechanisms to support the establishment of productive infection and to avoid host defense mechanisms, including promoting or decreasing inflammatory responses and regulating host machinery for protein synthesis. Viral interactions with the host enzymatic machinery, specifically kinases, can support the viral infectious process and downplay innate immune mechanisms, cumulatively leading to a more severe course of the disease. In this review, we will focus on how select equine viruses interact with host kinases to support viral multiplication.

IFN-γ-Based ELISpot as a New Tool to Detect Human Infections with Borna Disease Virus 1 (BoDV-1): A Pilot Study

More than 40 human infections with the zoonotic Borna disease virus 1 (BoDV-1) have been reported to German health authorities from endemic regions in southern and eastern Germany. Diagnosis of a confirmed case is based on the detection of BoDV-1 RNA or BoDV-1 antigen. In parallel, serological assays such as ELISA, immunoblots, and indirect immunofluorescence are in use to detect the seroconversion of Borna virus-reactive IgG in serum or cerebrospinal fluid (CSF). As immunopathogenesis in BoDV-1 encephalitis appears to be driven by T cells, we addressed the question of whether an IFN-γ-based ELISpot may further corroborate the diagnosis. For three of seven BoDV-1-infected patients, peripheral blood mononuclear cells (PBMC) with sufficient quantity and viability were retrieved. For all three patients, counts in the range from 12 to 20 spot forming units (SFU) per 250,000 cells were detected upon the stimulation of PBMC with a peptide pool covering the nucleocapsid protein of BoDV-1. Additionally, individual patients had elevated SFU upon stimulation with a peptide pool covering X or phosphoprotein. Healthy blood donors (n = 30) and transplant recipients (n = 27) were used as a control and validation cohort, respectively. In this pilot study, the BoDV-1 ELISpot detected cellular immune responses in human patients with BoDV-1 infection. Its role as a helpful diagnostic tool needs further investigation in patients with BoDV-1 encephalitis.

Human Infections with Borna Disease Virus 1 (BoDV-1) Primarily Lead to Severe Encephalitis: Further Evidence from the Seroepidemiological BoSOT Study in an Endemic Region in Southern Germany

More than 40 human cases of severe encephalitis caused by Borna disease virus 1 (BoDV-1) have been reported to German health authorities. In an endemic region in southern Germany, we conducted the seroepidemiological BoSOT study ("BoDV-1 after solid-organ transplantation") to assess whether there are undetected oligo- or asymptomatic courses of infection. A total of 216 healthy blood donors and 280 outpatients after solid organ transplantation were screened by a recombinant BoDV-1 ELISA followed by an indirect immunofluorescence assay (iIFA) as confirmatory test. For comparison, 288 serum and 258 cerebrospinal fluid (CSF) samples with a request for tick-borne encephalitis (TBE) diagnostics were analyzed for BoDV-1 infections. ELISA screening reactivity rates ranged from 3.5% to 18.6% depending on the cohort and the used ELISA antigen, but only one sample of a patient from the cohort with requested TBE diagnostics was confirmed to be positive for anti-BoDV-1-IgG by iIFA. In addition, the corresponding CSF sample of this patient with a three-week history of severe neurological disease tested positive for BoDV-1 RNA. Due to the iIFA results, all other results were interpreted as false-reactive in the ELISA screening. By linear serological epitope mapping, cross-reactions with human and bacterial proteins were identified as possible underlying mechanism for the false-reactive ELISA screening results. In conclusion, no oligo- or asymptomatic infections were detected in the studied cohorts. Serological tests based on a single recombinant BoDV-1 antigen should be interpreted with caution, and an iIFA should always be performed in addition.

Vaccination against Borna Disease: Overview, Vaccine Virus Characterization and Investigation of Live and Inactivated Vaccines

(1) Background: Vaccination of horses and sheep against Borna disease (BD) was common in endemic areas of Germany in the 20th century but was abandoned in the early 1990s. The recent occurrence of fatal cases of human encephalitis due to Borna disease virus 1 (BoDV-1) has rekindled the interest in vaccination. (2) Methods: The full genomes of the BD live vaccine viruses "Dessau" and "Giessen" were sequenced and analyzed for the first time. All vaccination experiments followed a proof-of-concept approach. Dose-titration infection experiments were performed in rabbits, based on both cell culture- and brain-derived viruses at various doses. Inactivated vaccines against BD were produced from concentrated cell culture supernatants and investigated in rabbits and horses. The BoDV-1 live vaccine "Dessau" was administered to horses and antibody profiles were determined. (3) Results: The BD live vaccine viruses "Dessau" and "Giessen" belong to clusters 3 and 4 of BoDV-1. Whereas the "Giessen" virus does not differ substantially from field viruses, the "Dessau" virus shows striking differences in the M gene and the N-terminal part of the G gene. Rabbits infected with high doses of cell-cultured virus developed neutralizing antibodies and were protected from disease, whereas rabbits infected with low doses of cell-cultured virus, or with brain-derived virus did not. Inactivated vaccines were administered to rabbits and horses, following pre-defined vaccination schemes consisting of three vaccine doses of either adjuvanted or nonadjuvanted inactivated virus. Their immunogenicity and protective efficacy were compared to the BD live vaccine "Dessau". Seventy per cent of horses vaccinated with the BD live vaccine "Dessau" developed neutralizing antibodies after vaccination. (4) Conclusion: Despite a complex evasion of immunological responses by bornaviruses, some vaccination approaches can protect against clinical disease. For optimal effectiveness, vaccines should be administered at high doses, following vaccination schemes consisting of three vaccine doses as basic immunization. Further investigations are necessary in order to investigate and improve protection against infection and to avoid side effects.

Molecular epidemiology of human Borna disease virus 1 infection revisited

Borna disease virus 1 (BoDV-1) strains attracted public interest by recently reported rare fatal encephalitis cases in Germany. Previously, human BoDV-1 infection was suggested to contribute to psychiatric diseases. Clinical outcomes (encephalitis vs. psychiatric disease) and epidemiology (zoonotic vs. human-to-human transmission) are still controversial. Here, phylogenetic analyses of 18 human and 4 laboratory strains revealed close genomic homologies both in distant geographical regions, and different clinical entities. Single unique amino acid mutations substantiated the authenticity of human strains. No matching was found with those of shrew strains in the same cluster 4, arguing against zoonosis. Opposite epidemiology concepts should be equally considered.

Reverse Genetics and Artificial Replication Systems of Borna Disease Virus 1

Borna disease virus 1 (BoDV-1) is a neurotropic RNA virus belonging to the family Bornaviridae within the order Mononegavirales. Whereas BoDV-1 causes neurological and behavioral disorders, called Borna disease (BD), in a wide range of mammals, its virulence in humans has been debated for several decades. However, a series of case reports in recent years have established the nature of BoDV-1 as a zoonotic pathogen that causes fatal encephalitis in humans. Although many virological properties of BoDV-1 have been revealed to date, the mechanism by which it causes fatal encephalitis in humans remains unclear. In addition, there are no effective vaccines or antiviral drugs that can be used in clinical practice. A reverse genetics approach to generating replication-competent recombinant viruses from full-length cDNA clones is a powerful tool that can be used to not only understand viral properties but also to develop vaccines and antiviral drugs. The rescue of recombinant BoDV-1 (rBoDV-1) was first reported in 2005. However, due to the slow nature of the replication of this virus, the rescue of high-titer rBoDV-1 required several months, limiting the use of this system. This review summarizes the history of the reverse genetics and artificial replication systems for orthobornaviruses and explores the recent progress in efforts to rescue rBoDV-1.

Tissue Distribution of Parrot Bornavirus 4 (PaBV-4) in Experimentally Infected Young and Adult Cockatiels (Nymphicus hollandicus)

Proventricular dilatation disease (PDD) caused by parrot bornavirus (PaBV) infection is an often-fatal disease known to infect Psittaciformes. The impact of age at the time of PaBV infection on organ lesions and tissue distribution of virus antigen and RNA remains largely unclear. For this purpose, tissue sections of 11 cockatiels intravenously infected with PaBV-4 as adults or juveniles, respectively, were examined via histology, immunohistochemistry applying a phosphoprotein (P) antibody directed against the bornaviral phosphoprotein and in situ hybridisation to detect viral RNA in tissues. In both groups of adult- and juvenile-infected cockatiels, widespread tissue distribution of bornaviral antigen and RNA as well as histologic inflammatory lesions were demonstrated. The latter appeared more severe in the central nervous system in adults and in the proventriculus of juveniles, respectively. During the study, central nervous symptoms and signs of gastrointestinal affection were only demonstrated in adult birds. Our findings indicate a great role of the age at the time of infection in the development of histopathological lesions and clinical signs, and thus provide a better understanding of the pathogenesis, possible virus transmission routes, and the development of carrier birds posing a risk to psittacine collections.

Human Borna disease virus 1 encephalitis shows marked pro-inflammatory biomarker and tissue immunoactivation during the course of disease

Human Borna disease virus 1 (BoDV-1) encephalitis is a severe emerging disease with a very high case-fatality rate. While the clinical disease, case definitions, diagnostic algorithms and neuropathology have been described, very little is known about the immunological processes of human BoDV-1 encephalitis. Here, we analyzed serum and cerebrospinal fluid (CSF) samples from 10 patients with fatal BoDV-1 encephalitis for changes of different cytokines, chemokines, growth factors and other biomarkers over time. From one of these individuals, also autoptic formalin-fixed brain tissue was analyzed for the expression of inflammatory biomarkers by mRNA levels and immunostaining; in a further patient, only formalin-fixed brain tissue was available and examined in addition. A marked and increasing immune activation from the initial phase to the last phase of acute BoDV-1 encephalitis is shown in serum and CSF, characterized by cytokine concentration changes (IFNγ, IL-5, IL-6, IL-9, IL-10, IL-12p40, IL-13, IL-18, TGF-β1) with a predominantly pro-inflammatory pattern over time. IFNγ production was demonstrated in endothelial cells, astrocytes and microglia, IL-6 in activated microglia, and TGF-β1 in endothelial cells, activated astrocytes and microglia. This was paralleled by an increase of chemokines (CCL-2, CCL-5, CXCL-10, IL-8) to attract immune cells to the site of infection, contributing to inflammation and tissue damage. Pathologically low growth factor levels (BDNF, β-NGF, PDGF) were seen. Changed levels of arginase and sTREM further fostered the pro-inflammatory state. This dysbalanced, pro-inflammatory state likely contributes importantly to the fatal outcome of human BoDV-1 encephalitis, and might be a key target for possible treatment attempts.

Healthcare-associated exposure to Borna disease virus 1 (BoDV-1)

The Borna disease virus 1 (BoDV-1) causes severe and often fatal encephalitis in humans. The virus is endemic in parts of Germany, Liechtenstein, Switzerland and Austria. As an increasing number of human BoDV-1 encephalitis cases is being diagnosed, the chance for healthcare professionals to come into contact with infected tissues and bodily fluids from patients with known acute bornavirus encephalitis is also increasing. Therefore, risk assessments are needed. Based on three different incidences of possible exposure to BoDV-1 including an autopsy knife injury, a needlestick injury, and a spill accident with cerebrospinal fluid from patients with acute BoDV-1 encephalitis, we perform risk assessments and review published data. BoDV-1 infection status of the index patient's tissues and bodily fluids to which contact had occurred should be determined. There is only scarce evidence for possible postexposure prophylaxis, serology, and imaging in healthcare professionals who possibly came into contact with the virus. Despite decade-long laboratory work with BoDV-1, not a single clinically apparent laboratory infection has been published. Given the increasing number of severe or fatal BoDV-1 encephalitis cases, there is a growing need for efficacy-tested, potent antiviral therapeutics against BoDV-1 in humans, both in clinically ill patients and possibly as postexposure prophylaxis in healthcare professionals.

Development of a nonhuman primate model for mammalian bornavirus infection

Until recently, it was assumed that members of the family Bornaviridae could not induce severe disease in humans. Today, however, Borna disease virus 1 (BoDV-1), as well as the more recently emerged variegated squirrel bornavirus 1 (VSBV-1), are known as causative agents of lethal encephalitis in humans. In order to establish animal models reflecting the pathogenesis in humans and for countermeasure efficacy testing, we infected twelve rhesus macaques (Macaca mulatta) either with VSBV-1 or with BoDV-1. For each virus, three monkeys each were inoculated with 2 × 10⁴ focus forming units by the intracerebral route or by multiple peripheral routes (intranasal, conjunctival, intramuscular, and subcutaneous; same dose in total). All BoDV-1 and VSBV-1 intracerebrally infected monkeys developed severe neurological signs around 5 to 6 or 8 to 12 weeks postinfection, respectively. Focal myoclonus and tremors were the most prominent observations in BoDV-1 and VSBV-1-infected animals. VSBV-1-infected animals also showed behavioral changes. Only one BoDV-1 peripherally infected animal developed similar disease manifestations. All animals with severe clinical disease showed high viral loads in brain tissues and displayed perivascular mononuclear cuffs with a predominance of lymphocytes and similar meningeal inflammatory infiltrates. In summary, rhesus macaques intracerebrally infected with mammalian bornaviruses develop a human-like disease and may serve as surrogate models for human bornavirus infection.

miR-505 inhibits replication of Borna disease virus 1 via inhibition of HMGB1-mediated autophagy

Borna disease virus 1 (BoDV-1) is a highly neurotropic RNA virus which was recently demonstrated to cause deadly human encephalitis. Viruses can modulate microRNA expression, in turn modulating cellular immune responses and regulating viral replication. A previous study indicated that BoDV-1 infection down-regulated the expression of miR-505 in rats. However, the underlying mechanism of miR-505 during BoDV-1 infection remains unknown. In this study, we found that miR-505 can inhibit autophagy activation by down-regulating the expression of its target gene HMGB1, and ultimately inhibit the replication of BoDV-1. Specifically, we found that the expression of miR-505 was significantly down-regulated in rat primary neurons stably infected with BoDV-1. Overexpression of miR-505 can inhibit the replication of BoDV-1 in cells. Bioinformatics analysis and dual luciferase reporter gene detection confirmed that during BoDV-1 infection, the high-mobility group protein B1 (HMGB1) that mediates autophagy is the direct target gene of miR-505. The expression of HMGB1 was up-regulated after BoDV-1 infection, and overexpression of miR-505 could inhibit the expression of HMGB1. Autophagy-related detection found that after infection with BoDV-1, the expression of autophagy-related proteins and autophagy-related marker LC3 in neuronal cells was significantly up-regulated. Autophagy flow experiments and transmission electron microscopy also further confirmed that BoDV-1 infection activated HMGB1-mediated autophagy. Further regulating the expression of miR-505 found that overexpression of miR-505 significantly inhibited HMGB1-mediated autophagy. The discovery of this mechanism may provide new ideas and directions for the prevention and treatment of BoDV-1 infection in the future.

Antibodies against viral nucleo-, phospho-, and X protein contribute to serological diagnosis of fatal Borna disease virus 1 infections

Borna disease virus 1 (BoDV-1) causes rare but often fatal encephalitis in humans. Late diagnosis prohibits an experimental therapeutic approach. Here, we report a recent case of fatal BoDV-1 infection diagnosed on day 12 after hospitalization by detection of BoDV-1 RNA in the cerebrospinal fluid. In a retrospective analysis, we detect BoDV-1 RNA 1 day after hospital admission when the cell count in the cerebrospinal fluid is still normal. We develop a new ELISA using recombinant BoDV-1 nucleoprotein, phosphoprotein, and accessory protein X to detect seroconversion on day 12. Antibody responses are also shown in seven previously confirmed cases. The individual BoDV-1 antibody profiles show variability, but the usage of three different BoDV-1 antigens results in a more sensitive diagnostic tool. Our findings demonstrate that early detection of BoDV-1 RNA in cerebrospinal fluid and the presence of antibodies against at least two different viral antigens contribute to BoDV-1 diagnosis. Physicians in endemic regions should consider BoDV-1 infection in cases of unclear encephalopathy and initiate appropriate diagnostics at an early stage.

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Borna disease virus 1 causes fatal encephalitis upon zoonotic spillover infections

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An ELISA system using recombinant BoDV-1 N, X, and P proteins has been established

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Antibodies against at least two different BoDV-1 antigens corroborate seroconversion

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Early detection of viral RNA and antibodies could contribute to BoDV-1 diagnosis

Emerging Microbes & Infections - Original Article: Human Borna disease virus 1 (BoDV-1) encephalitis cases in the north and east of Germany

In 2021, three encephalitis cases due to the Borna disease virus 1 (BoDV-1) were diagnosed in the north and east of Germany. The patients were from the states of Thuringia, Saxony-Anhalt, and Lower Saxony. All were residents of known endemic areas for animal Borna disease but without prior diagnosed human cases. Except for one recently detected case in the state of Brandenburg, all >30 notified cases had occurred in, or were linked to, the southern state of Bavaria. Of the three detected cases described here, two infections were acute, while one infection was diagnosed retrospectively from archived brain autopsy tissue samples. One of the acute cases survived, but is permanently disabled. The cases were diagnosed by various techniques (serology, molecular assays, and immunohistology) following a validated testing scheme and adhering to a proposed case definition. Two cases were classified as confirmed BoDV-1 encephalitis, while one case was a probable infection with positive serology and typical brain magnetic resonance imaging, but without molecular confirmation. Of the three cases, one full virus genome sequence could be recovered. Our report highlights the need for awareness of a BoDV-1 etiology in cryptic encephalitis cases in all areas with known animal Borna disease endemicity in Europe, including virus-endemic regions in Austria, Liechtenstein, and Switzerland. BoDV-1 should be actively tested for in acute encephalitis cases with residence or rural exposure history in known Borna disease-endemic areas.

The Borna Disease Virus 2 (BoDV-2) Nucleoprotein Is a Conspecific Protein That Enhances BoDV-1 RNA-Dependent RNA Polymerase Activity

An RNA virus-based episomal vector (REVec) based on Borna disease virus 1 (BoDV-1) is a promising viral vector that achieves stable and long-term gene expression in transduced cells. However, the onerous procedure of reverse genetics used to generate an REVec is one of the challenges that must be overcome to make REVec technologies practical for use. In this study, to resolve the problems posed by reverse genetics, we focused on BoDV-2, a conspecific virus of BoDV-1 in the Mammalian 1 orthobornavirus. We synthesized the BoDV-2 nucleoprotein (N) and phosphoprotein (P) according to the reference sequences and evaluated their effects on the RNA polymerase activity of the BoDV-1 large protein (L) and viral replication. In the minireplicon assay, we found that BoDV-2 N significantly enhanced BoDV-1 polymerase activity and that BoDV-2 P supported further enhancement of this activity by N. A single amino acid substitution assay identified serine at position 30 of BoDV-2 N and alanine at position 24 of BoDV-2 P as critical amino acid residues for the enhancement of BoDV-1 polymerase activity. In reverse genetics, conversely, BoDV-2 N alone was sufficient to increase the rescue efficiency of the REVec. We showed that the REVec can be rescued directly from transfected 293T cells by using BoDV-2 N as a helper plasmid without cocultivation with Vero cells and following several weeks of passage. In addition, a chimeric REVec harboring the BoDV-2 N produced much higher levels of transgene mRNA and genomic RNA than the wild-type REVec in transduced cells. Our results contribute to not only improvements to the REVec system but also to understanding of the molecular regulation of orthobornavirus polymerase activity. IMPORTANCE Borna disease virus 1 (BoDV-1), a prototype virus of the species Mammalian 1 orthobornavirus, is a nonsegmented negative-strand RNA virus that persists in the host nucleus. The nucleoprotein (N) of BoDV-1 encapsidates genomic and antigenomic viral RNA, playing important roles in viral transcription and replication. In this study, we demonstrated that the N of BoDV-2, another genotype in the species Mammalian 1 orthobornavirus, can participate in the viral ribonucleoprotein complex of BoDV-1 and enhance the activity of BoDV-1 polymerase (L) in both the BoDV-1 minireplicon assay and reverse genetics system. Chimeric recombinant BoDV-1 expressing BoDV-2 N but not BoDV-1 N showed higher transcription and replication levels, whereas the propagation and infectious particle production of the chimeric virus were comparable to those of wild-type BoDV-1, suggesting that the level of viral replication in the nucleus is not directly involved in the progeny virion production of BoDVs. Our results demonstrate a molecular mechanism of bornaviral polymerase activity, which will contribute to further development of vector systems using orthobornaviruses.

Genetic stability of the open reading frame 2 (ORF2) of borna disease virus 1 (BoDV-1) distributed in cattle in Hokkaido

Borna disease virus (BoDV) is a neurotropic virus that causes several infections in humans and neurological diseases in a wide range of animals worldwide. BoDV-1 has been molecularly and serologically detected in many domestic and wild animals in Japan; however, the genetic diversity of this virus and the origin of its infection are not fully understood. In this study, we investigated BoDV-1 infection and genetic diversity in samples collected from animals in Hokkaido between 2006 and 2020. The analysis was performed by focusing on the P region of BoDV-1 for virus detection. The presence of BoDV-1 RNA was observed in samples of brain tissue and various organs derived from persistently infected cattle. Moreover, after inoculation, BoDV-positive brains were isolated from neonatal rats. The gene sequences of the P region of BoDV obtained from the rat brain were in the same cluster as the P region of the virus isolated from the original bovine. Thus, genetic variation in BoDV-1 was extremely low. The phylogenetic analysis revealed that BoDV-1 isolates obtained in this study were part of the same cluster, which suggested that BoDV-1 of the same cluster was widespread among animals in Hokkaido.

Investigation of fatal human Borna disease virus 1 encephalitis outside the previously known area for human cases, Brandenburg, Germany - a case report

Background

The true burden and geographical distribution of human Borna disease virus 1 (BoDV-1) encephalitis is unknown. All detected cases so far have been recorded in Bavaria, southern Germany.

Case presentation

A retrospective laboratory and epidemiological investigation of a 2017 case of fatal encephalitis in a farmer in Brandenburg, northeast Germany, demonstrated BoDV-1 as causative agent by polymerase chain reaction, immunohistochemistry and in situ hybridization. Next-generation sequencing showed that the virus belonged to a cluster not known to be endemic in Brandenburg. The investigation was triggered by a recent outbreak of animal Borna disease in the region. Multiple possible exposures were identified. The next-of-kin were seronegative.

Conclusions

The investigation highlights clinical awareness for human BoDV-1 encephalitis which should be extended to all areas endemic for animal Borna disease. All previously diagnosed human cases had occurred > 350 km further south. Further testing of shrews and livestock with Borna disease may show whether this BoDV-1 cluster is additionally endemic in the northwest of Brandenburg.

Active Case Finding of Current Bornavirus Infections in Human Encephalitis Cases of Unknown Etiology, Germany, 2018-2020

Human bornavirus encephalitis is a severe and often fatal infection caused by variegated squirrel bornavirus 1 (VSBV-1) and Borna disease virus 1 (BoDV-1). We conducted a prospective study of bornavirus etiology of encephalitis cases in Germany during 2018-2020 by using a serologic testing scheme applied along proposed graded case definitions for VSBV-1, BoDV-1, and unspecified bornavirus encephalitis. Of 103 encephalitis cases of unknown etiology, 4 bornavirus infections were detected serologically. One chronic case was caused by VSBV-1 after occupational-related contact of a person with exotic squirrels, and 3 acute cases were caused by BoDV-1 in virus-endemic areas. All 4 case-patients died. Bornavirus etiology could be confirmed by molecular methods. Serologic testing for these cases was virus specific, discriminatory, and a practical diagnostic option for living patients if no brain tissue samples are available. This testing should be guided by clinical and epidemiologic suspicions, such as residence in virus-endemic areas and animal exposure.

First isolation, in-vivo and genomic characterization of zoonotic variegated squirrel Bornavirus 1 (VSBV-1) isolates

The variegated squirrel bornavirus 1 (VSBV-1), a member of the family Bornaviridae, was discovered in 2015 in a series of lethal human infections. Screening approaches revealed kept exotic squirrels as the putative source of infection. Infectious virus was successfully isolated by co-cultivation of infected primary squirrel cells with permanent cell lines. For in vivo characterization, neonatal and adult Lewis rats were inoculated either intracranially, intranasally or subcutaneously. After 4.5 months, three out of fifteen neonatal intracranially inoculated rats were VSBV-1 genome positive in the central nervous system without showing clinical signs. Pathohistological examination revealed a non-purulent encephalitis. While infection of immune incompetent rats (neonatal) using the type species of mammalian bornaviruses, the Borna disease virus 1, proceed to an immune tolerant status, VSBV-1 infection could result in inflammation of neuronal tissue. Sequencing showed minor adaptations within the VSBV-1 genome comparing to the viral genomes from infected squirrels, cell cultures or rat tissues. In conclusion, we were able to generate the first VSBV-1 isolates and provide in vivo animal model data in Lewis rats revealing substantial differences between VSBV-1 and BoDV-1. Furthermore, the presented data are a precondition for insights into the transmission and pathogenesis of this novel zoonotic pathogen.

New World camelids are sentinels for the presence of Borna disease virus

Borna disease (BD), a frequently fatal neurologic disorder caused by Borna disease virus 1 (BoDV-1), has been observed for decades in horses, sheep, and other mammals in certain regions of Europe. The bicoloured white-toothed shrew (Crocidura leucodon) was identified as a persistently infected species involved in virus transmission. Recently, BoDV-1 attracted attention as a cause of fatal encephalitis in humans. Here, we report investigations on BoDV-1-infected llamas from a farm in a BD endemic area of Switzerland, and alpacas from holdings in a region of Germany where BD was last seen in the 1960s but not thereafter. All New World camelids showed apathy and abnormal behaviour, necessitating euthanasia. Histologically, severe non-suppurative meningoencephalitis with neuronal Joest-Degen inclusion bodies was observed. BoDV-1 was confirmed by immunohistology, RT-qPCR, and sequencing in selected animals. Analysis of the llama herd over 20 years showed that losses due to clinically suspected BD increased within the last decade. BoDV-1 whole-genome sequences from one Swiss llama and one German alpaca and-for comparison-from one Swiss horse and one German shrew were established. They represent the first published whole-genome sequences of BoDV-1 clusters 1B and 3, respectively. Our analysis suggests that New World camelids may have a role as a sentinel species for BoDV-1 infection, even when symptomatic cases are lacking in other animal species.

Full-length genomic sequencing and characterization of Borna disease virus 1 isolates: Lessons in epidemiology

Borna disease virus 1 (BoDV-1) is a nonsegmented, negative-strand RNA virus that infects mammals including humans. BoDV-1 strains occur globally, dominate the species Mammalian 1 bornavirus, and display highly conserved genomes and persistent infection (brain, blood). Subclinical infections prevail but the rare fatal outcomes even in people need awareness and risk assessment. Although BoDV-1 strains were successfully isolated, only limited full genomic sequences are available. In this study, the entire genomes of two natural BoDV-1 isolates (Hu-H2, Equ-Cres) and one vaccine strain (DessVac) were sequenced. They were compared with 20 genomes and 20 single-gene sequences (N and P) of worldwide human strains from psychiatric and neurologic patients and animal strains from horses with Borna disease available at GenBank. Phylogenetic analyses confirmed a low divergence not exceeding 5.55%, 5.34%, and 4.94% at the genome, P-gene, and N-gene level, respectively, characteristic of BoDV-1. Human viruses tended to cluster at the country level but appeared to be independent of hosts' diseases and/or time of isolation. Notably, our data also indicated that human viruses provided individual genetic signatures but exhibited no distinct genotypes that separated them from animal strains. Sequence similarities thus occurred between different host species and distant geographic regions, supporting global BoDV-1 prevalence. Overall low genetic divergence among BoDV-1 viruses shown here also argued against zoonotic concepts, requiring further clarification beyond sequence similarities. Finally, unlike shared sequence conservation, phenotyping of natural and laboratory variants revealed that they manipulated host cells differently, underpinning the authenticity of the human BoDV-1 strains.

Borna disease outbreak with high mortality in an alpaca herd in a previously unreported endemic area in Germany

Borna disease virus 1 (BoDV-1) is the causative agent of Borna disease, an often fatal neurologic condition of domestic mammals, including New World camelids, in endemic areas in Central Europe. Recently, BoDV-1 gained further attention by the confirmation of fatal zoonotic infections in humans. Although Borna disease and BoDV-1 have been described already over the past decades, comprehensive reports of Borna disease outbreaks in domestic animals employing state-of-the-art diagnostic methods are missing. Here, we report a series of BoDV-1 infections in a herd of 27 alpacas (Vicugna pacos) in the federal state of Brandenburg, Germany, which resulted in eleven fatalities (41%) within ten months. Clinical courses ranged from sudden death without previous clinical signs to acute or chronic neurologic disease with death occurring after up to six months. All animals that underwent necropsy exhibited a non-suppurative encephalitis. In addition, six apparently healthy seropositive individuals were identified within the herd, suggesting subclinical BoDV-1 infections. In infected animals, BoDV-1 RNA and antigen were mainly restricted to the central nervous system and the eye, and sporadically detectable in large peripheral nerves and neuronal structures in other tissues. Pest control measures on the farm resulted in the collection of a BoDV-1-positive bicoloured white-toothed shrew (Crocidura leucodon), while all other trapped small mammals were negative. A phylogeographic analysis of BoDV-1 sequences from the alpacas, the shrew and BoDV-1-positive equine cases from the same region in Brandenburg revealed a previously unreported endemic area of BoDV-1 cluster 4 in North-Western Brandenburg. In conclusion, alpacas appear to be highly susceptible to BoDV-1 infection and display a highly variable clinical picture ranging from peracute death to subclinical forms. In addition to horses and sheep, they can serve as sensitive sentinels used for the identification of endemic areas.

Bornavirus Encephalitis Shows a Characteristic Magnetic Resonance Phenotype in Humans

OBJECTIVE

The number of diagnosed fatal encephalitis cases in humans caused by the classical Borna disease virus (BoDV-1) has been increasing, ever since it was proved that BoDV-1 can cause human infections. However, awareness of this entity is low, and a specific imaging pattern has not yet been identified. We therefore provide the first comprehensive description of the morphology of human BoDV-1 encephalitis, with histopathological verification of imaging abnormalities.

METHODS

In an institutional review board-approved multicenter study, we carried out a retrospective analysis of 55 magnetic resonance imaging (MRI) examinations of 19 patients with confirmed BoDV-1 encephalitis. Fifty brain regions were analyzed systematically (T1w, T2w, T2*w, T1w + Gd, and DWI), in order to discern a specific pattern of inflammation. Histopathological analysis of 25 locations in one patient served as correlation for MRI abnormalities.

RESULTS

Baseline imaging, acquired at a mean of 11 ± 10 days after symptom onset, in addition to follow-up scans of 16 patients, revealed characteristic T2 hyperintensities with a predilection for the head of the caudate nucleus, insula, and cortical spread to the limbic system, whereas the occipital lobes and cerebellar hemispheres were unaffected. This gradient was confirmed by histology. Nine patients (47.4%) developed T1 hyperintensities of the basal ganglia, corresponding to accumulated lipid phagocytes on histology and typical for late-stage necrosis.

INTERPRETATION

BoDV-1 encephalitis shows a distinct pattern of inflammation in both the early and late stages of the disease. Its appearance can mimic sporadic Creutzfeldt-Jakob disease on MRI and should be considered a differential diagnosis in the case of atypical clinical presentation. ANN NEUROL 2020;88:723-735.

Update on immunopathology of bornavirus infections in humans and animals

Knowledge on bornaviruses has expanded tremendously during the last decade through detection of novel bornaviruses and endogenous bornavirus-like elements in many eukaryote genomes, as well as by confirmation of insectivores as reservoir species for classical Borna disease virus 1 (BoDV-1). The most intriguing finding was the demonstration of the zoonotic potential of lethal human bornavirus infections caused by a novel bornavirus of different squirrel species (variegated squirrel 1 bornavirus, VSBV-1) and by BoDV-1 known as the causative agent for the classical Borna disease in horses and sheep. Whereas a T cell-mediated immunopathology has already been confirmed as key disease mechanism for infection with BoDV-1 by experimental studies in rodents, the underlying pathomechanisms remain less clear for human bornavirus infections, infection with other bornaviruses or infection of reservoir species. Thus, an overview of current knowledge on the pathogenesis of bornavirus infections focusing on immunopathology is given.

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

BACKGROUND

Squirrels (family Sciuridae) are globally distributed members of the order Rodentia with wildlife occurrence in indigenous and non-indigenous regions (as invasive species) and frequent presence in zoological gardens and other holdings. Multiple species introductions, strong inter-species competition as well as the recent discovery of a novel zoonotic bornavirus resulted in increased research interest on squirrel pathogens. Therefore we aimed to test a variety of squirrel species for representatives of three virus families.

METHODS

Several species of the squirrel subfamilies Sciurinae, Callosciurinae and Xerinae were tested for the presence of polyomaviruses (PyVs; family Polyomaviridae) and herpesviruses (HVs; family Herpesviridae), using generic nested polymerase chain reaction (PCR) with specificity for the PyV VP1 gene and the HV DNA polymerase (DPOL) gene, respectively. Selected animals were tested for the presence of bornaviruses (family Bornaviridae), using both a broad-range orthobornavirus- and a variegated squirrel bornavirus 1 (VSBV-1)-specific reverse transcription-quantitative PCR (RT-qPCR).

RESULTS

In addition to previously detected bornavirus RNA-positive squirrels no more animals tested positive in this study, but four novel PyVs, four novel betaherpesviruses (BHVs) and six novel gammaherpesviruses (GHVs) were identified. For three PyVs, complete genomes could be amplified with long-distance PCR (LD-PCR). Splice sites of the PyV genomes were predicted in silico for large T antigen, small T antigen, and VP2 coding sequences, and experimentally confirmed in Vero and NIH/3T3 cells. Attempts to extend the HV DPOL sequences in upstream direction resulted in contiguous sequences of around 3.3 kilobase pairs for one BHV and two GHVs. Phylogenetic analysis allocated the novel squirrel PyVs to the genera Alpha- and Betapolyomavirus, the BHVs to the genus Muromegalovirus, and the GHVs to the genera Rhadinovirus and Macavirus.

CONCLUSIONS

This is the first report on molecular identification and sequence characterization of PyVs and HVs and the detection of bornavirus coinfections with PyVs or HVs in two squirrel species. Multiple detection of PyVs and HVs in certain squirrel species exclusively indicate their potential host association to a single squirrel species. The novel PyVs and HVs might serve for a better understanding of virus evolution in invading host species in the future.

Zoonotic spillover infections with Borna disease virus 1 leading to fatal human encephalitis, 1999-2019: an epidemiological investigation

BACKGROUND

In 2018-19, Borna disease virus 1 (BoDV-1), the causative agent of Borna disease in horses, sheep, and other domestic mammals, was reported in five human patients with severe to fatal encephalitis in Germany. However, information on case frequencies, clinical courses, and detailed epidemiological analyses are still lacking. We report the occurrence of BoDV-1-associated encephalitis in cases submitted to the Institute of Clinical Microbiology and Hygiene, Regensburg University Hospital, Regensburg, Germany, and provide a detailed description of newly identified cases of BoDV-1-induced encephalitis.

METHODS

All brain tissues from 56 encephalitis cases from Bavaria, Germany, of putative viral origin (1999-2019), which had been submitted for virological testing upon request of the attending clinician and stored for stepwise diagnostic procedure, were systematically screened for BoDV-1 RNA. Two additional BoDV-1-positive cases were contributed by other diagnostic centres. Positive results were confirmed by deep sequencing, antigen detection, and determination of BoDV-1-reactive antibodies in serum and cerebrospinal fluid. Clinical and epidemiological data from infected patients were collected and analysed.

FINDINGS

BoDV-1 RNA and bornavirus-reactive antibodies were detected in eight newly analysed encephalitis cases and the first human BoDV-1 isolate was obtained from an unequivocally confirmed human BoDV-1 infection from the endemic area. Six of the eight BoDV-1-positive patients had no record of immunosuppression before the onset of fatal disease, whereas two were immunocompromised after solid organ transplantation. Typical initial symptoms were headache, fever, and confusion, followed by various neurological signs, deep coma, and severe brainstem involvement. Seven of nine patients with fatal encephalitis of unclear cause were BoDV-1 positive within one diagnostic centre. BoDV-1 sequence information and epidemiological analyses indicated independent spillover transmissions most likely from the local wild animal reservoir.

INTERPRETATION

BoDV-1 infection has to be considered as a potentially lethal zoonosis in endemic regions with reported spillover infections in horses and sheep. BoDV-1 infection can result in fatal encephalitis in immunocompromised and apparently healthy people. Consequently, all severe encephalitis cases of unclear cause should be tested for bornaviruses especially in endemic regions.

FUNDING

German Federal Ministry of Education and Research.

The neuropathology of fatal encephalomyelitis in human Borna virus infection

After many years of controversy, there is now recent and solid evidence that classical Borna disease virus 1 (BoDV-1) can infect humans. On the basis of six brain autopsies, we provide the first systematic overview on BoDV-1 tissue distribution and the lesion pattern in fatal BoDV-1-induced encephalitis. All brains revealed a non-purulent, lymphocytic sclerosing panencephalomyelitis with detection of BoDV-1-typical eosinophilic, spherical intranuclear Joest–Degen inclusion bodies. While the composition of histopathological changes was constant, the inflammatory distribution pattern varied interindividually, affecting predominantly the basal nuclei in two patients, hippocampus in one patient, whereas two patients showed a more diffuse distribution. By immunohistochemistry and RNA in situ hybridization, BoDV-1 was detected in all examined brain tissue samples. Furthermore, infection of the peripheral nervous system was observed. This study aims at raising awareness to human bornavirus encephalitis as differential diagnosis in lymphocytic sclerosing panencephalomyelitis. A higher attention to human BoDV-1 infection by health professionals may likely increase the detection of more cases and foster a clearer picture of the disease.