Development of a nonhuman primate model for mammalian bornavirus infection

Neuropathology, pathomechanism, and transmission in zoonotic Borna disease virus 1 infection: a systematic review

Borna disease, which is a severe encephalitis that primarily affects horses and sheep, has been recognised for over two centuries. Borna disease virus 1 (BoDV-1) has been identified as a cause of a predominantly fatal encephalitis in humans. Little scientific data exist regarding the virus' transmission, entry portal, and excretion routes. Lesional patterns, immunological responses, and pathogenetic mechanisms remain largely unexplored in both reservoir and dead-end hosts. This systematic review compiles current knowledge on these aspects and provides guidance for future research. PubMed, ScienceDirect, and EBSCO were searched for publications from Jan 1, 2000, to April 30, 2024. 823 records were found, of which 41 studies were included. This systematic review discusses BoDV-1 transmission, pathogenesis, histopathological changes, and immunology in both reservoir and dead-end hosts, with special regard for humans. The exact propagation mechanisms, entry portal, and viral spread within the CNS are not entirely clear in humans. Although more data exist in animals, much remains hypothetical. Future research should focus on identifying potential entry sites and viral spread in dead-end hosts, which could help to clarify the pathogenesis and lesion distribution in the CNS, thereby contributing to a better understanding of BoDV-1 infection in humans and parallels with animal infections.

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.

First detected geographical cluster of BoDV-1 encephalitis from same small village in two children: therapeutic considerations and epidemiological implications

BACKGROUND

The Borna disease virus (BoDV-1) is an emerging zoonotic virus causing severe and mostly fatal encephalitis in humans.

METHODS AND RESULTS

A local cluster of fatal BoDV-1 encephalitis cases was detected in the same village three years apart affecting two children. While the first case was diagnosed late in the course of disease, a very early diagnosis and treatment attempt facilitated by heightened awareness was achieved in the second case. Therapy started as early as day 12 of disease. Antiviral therapy encompassed favipiravir and ribavirin, and, after bioinformatic modelling, also remdesivir. As the disease is immunopathogenetically mediated, an intensified anti-inflammatory therapy was administered. Following initial impressive clinical improvement, the course was also fatal, although clearly prolonged. Viral RNA was detected by qPCR in tear fluid and saliva, constituting a possible transmission risk for health care professionals. Highest viral loads were found post mortem in the olfactory nerve and the limbic system, possibly reflecting the portal of entry for BoDV-1. Whole exome sequencing in both patients yielded no hint for underlying immunodeficiency. Full virus genomes belonging to the same cluster were obtained in both cases by next-generation sequencing. Sequences were not identical, indicating viral diversity in natural reservoirs. Specific transmission events or a common source of infection were not found by structured interviews. Patients lived 750m apart from each other and on the fringe of the settlement, a recently shown relevant risk factor.

CONCLUSION

Our report highlights the urgent necessity of effective treatment strategies, heightened awareness and early diagnosis. Gaps of knowledge regarding risk factors, transmission events, and tailored prevention methods become apparent. Whether this case cluster reflects endemicity or a geographical hot spot needs further investigation.

Animal Model Alternatives in Filovirus and Bornavirus Research

The order Mononegavirales contains a variety of highly pathogenic viruses that may infect humans, including the families Filoviridae, Bornaviridae, Paramyxoviridae, and Rhabodoviridae. Animal models have historically been important to study virus pathogenicity and to develop medical countermeasures. As these have inherent shortcomings, the rise of microphysiological systems and organoids able to recapitulate hallmarks of the diseases caused by these viruses may have enormous potential to add to or partially replace animal modeling in the future. Indeed, microphysiological systems and organoids are already used in the pharmaceutical R&D pipeline because they are prefigured to overcome the translational gap between model systems and clinical studies. Moreover, they may serve to alleviate ethical concerns related to animal research. In this review, we discuss the value of animal model alternatives in human pathogenic filovirus and bornavirus research. The current animal models and their limitations are presented followed by an overview of existing alternatives, such as organoids and microphysiological systems, which might help answering open research questions.

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.