Implications of the antiviral drug favipiravir on rabies immunoglobulin for post-exposure prophylaxis of rabies in mice model with category III-like exposures

β-d-N4-hydroxycytidine, a metabolite of molnupiravir, exhibits in vitro antiviral activity against rabies virus

Rabies is a fatal neurological disorder caused by rabies virus (RABV) infection. Approximately 60,000 patients die from rabies annually, and there are no effective treatments for this disease. Nucleoside analogs are employed as antiviral drugs based on their broad antiviral spectrum, and certain nucleoside analogs have been reported to exhibit anti-RABV activity. The nucleoside analog β-d-N4-hydroxycytidine (NHC) has antiviral effects against a range of RNA viruses. Molnupiravir (MPV), a prodrug of NHC, is clinically used as an oral antiviral drug for coronavirus infections. Despite its broad-spectrum activity, the antiviral activity of NHC against RABV remains unclear. In this study, we reveal that NHC exhibits comparable in vitro anti-RABV activity as ribavirin and favipiravir (also known as T-705) with a 90% effective concentration of 6 μM in mouse neuroblastoma cells. NHC reduced viral loads in neuronal and nonneuronal cells in a dose-dependent manner. Both laboratory and field RABVs (fixed and street strains, respectively) were susceptible to NHC. However, no increase in survival or reduction in viral titers in the brain was observed in RABV-infected mice treated prophylactically with MPV. These findings highlight the potential and challenges of NHC in the treatment of RABV infection.

A Robust Phenotypic High-Throughput Antiviral Assay for the Discovery of Rabies Virus Inhibitors

Rabies virus (RABV) causes severe neurological symptoms in mammals. The disease is almost inevitably lethal as soon as clinical symptoms appear. The use of rabies immunoglobulins (RIG) and vaccination in post-exposure prophylaxis (PEP) can provide efficient protection, but many people do not receive this treatment due to its high cost and/or limited availability. Highly potent small molecule antivirals are urgently needed to treat patients once symptoms develop. In this paper, we report on the development of a high-throughput phenotypic antiviral screening assay based on the infection of BHK-21 cells with a fluorescent reporter virus and high content imaging readout. The assay was used to screen a repurposing library of 3681 drugs (all had been studied in phase 1 clinical trials). From this series, salinomycin was found to selectively inhibit viral replication by blocking infection at the entry stage. This shows that a high-throughput assay enables the screening of large compound libraries for the purposes of identifying inhibitors of RABV replication. These can then be optimized through medicinal chemistry efforts and further developed into urgently needed drugs for the treatment of symptomatic rabies.

Neuroimmunology of rabies: New insights into an ancient disease

Rabies is an ancient neuroinvasive viral (genus Lyssavirus, family Rhabdoviridae) disease affecting approximately 59,000 people worldwide. The central nervous system (CNS) is targeted, and rabies has a case fatality rate of almost 100% in humans and animals. Rabies is entirely preventable through proper vaccination, and thus, the highest incidence is typically observed in developing countries, mainly in Africa and Asia. However, there are still cases in European countries and the United States. Recently, demographic, increasing income levels, and the coronavirus disease 2019 (COVID-19) pandemic have caused a massive raising in the animal population, enhancing the need for preventive measures (e.g., vaccination, surveillance, and animal control programs), postexposure prophylaxis, and a better understanding of rabies pathophysiology to identify therapeutic targets, since there is no effective treatment after the onset of clinical manifestations. Here, we review the neuroimmune biology and mechanisms of rabies. Its pathogenesis involves a complex and poorly understood modulation of immune and brain functions associated with metabolic, synaptic, and neuronal impairments, resulting in fatal outcomes without significant histopathological lesions in the CNS. In this context, the neuroimmunological and neurochemical aspects of excitatory/inhibitory signaling (e.g., GABA/glutamate crosstalk) are likely related to the clinical manifestations of rabies infection. Uncovering new links between immunopathological mechanisms and neurochemical imbalance will be essential to identify novel potential therapeutic targets to reduce rabies morbidity and mortality.

Rabies in a postpandemic world: resilient reservoirs, redoubtable riposte, recurrent roadblocks, and resolute recidivism

Rabies is an ancient disease. Two centuries since Pasteur, fundamental progress occurred in virology, vaccinology, and diagnostics-and an understanding of pathobiology and epizootiology of rabies in testament to One Health-before common terminological coinage. Prevention, control, selective elimination, and even the unthinkable-occasional treatment-of this zoonosis dawned by the twenty-first century. However, in contrast to smallpox and rinderpest, eradication is a wishful misnomer applied to rabies, particularly post-COVID-19 pandemic. Reasons are minion. Polyhostality encompasses bats and mesocarnivores, but other mammals represent a diverse spectrum of potential hosts. While rabies virus is the classical member of the genus, other species of lyssaviruses also cause the disease. Some reservoirs remain cryptic. Although global, this viral encephalitis is untreatable and often ignored. As with other neglected diseases, laboratory-based surveillance falls short of the notifiable ideal, especially in lower- and middle-income countries. Calculation of actual burden defaults to a flux within broad health economic models. Competing priorities, lack of defined, long-term international donors, and shrinking local champions challenge human prophylaxis and mass dog vaccination toward targets of 2030 for even canine rabies impacts. For prevention, all licensed vaccines are delivered to the individual, whether parenteral or oral-essentially 'one and done'. Exploiting mammalian social behaviors, future 'spreadable vaccines' might increase the proportion of immunized hosts per unit effort. However, the release of replication-competent, genetically modified organisms selectively engineered to spread intentionally throughout a population raises significant biological, ethical, and regulatory issues in need of broader, transdisciplinary discourse. How this rather curious idea will evolve toward actual unconventional prevention, control, or elimination in the near term remains debatable. In the interim, more precise terminology and realistic expectations serve as the norm for diverse, collective constituents to maintain progress in the field.