Explore the vast range of titles available.

GS-5734 is a monophosphate prodrug of an adenosine nucleoside analog that showed therapeutic efficacy in a non-human primate model of Ebola virus infection. It has been administered under compassionate use to two Ebola patients, both of whom survived, and is currently in Phase 2 clinical development for treatment of Ebola virus disease. Here we report the antiviral activities of GS-5734 and the parent nucleoside analog across multiple virus families, providing evidence to support new indications for this compound against human viruses of significant public health concern.

Marburg virus (MARV) is a highly pathogenic virus associated with severe disease and mortality rates as high as 90%. Outbreaks of MARV are sporadic, deadly, and often characterized by a lack of resources and facilities to diagnose and treat patients. There are currently no approved vaccines or treatments, and the chaotic and infrequent nature of outbreaks, among other factors, makes testing new countermeasures during outbreaks ethically and logistically challenging. Without field efficacy studies, researchers must rely on animal models of MARV infection to assess the efficacy of vaccines and treatments, with the limitations being the accuracy of the animal model in recapitulating human pathogenesis. This review will compare various animal models to the available descriptions of human pathogenesis and aims to evaluate their effectiveness in modeling important aspects of Marburg virus disease.

Marburg virus (MARV) has caused outbreaks of filoviral hemorrhagic fever since its discovery in 1967. The largest and deadliest outbreak occurred in Angola in 2005, with 252 cases and 227 deaths. In 2014, we developed a mouse-adapted MARV, Angola variant through serial passaging in mice. The mouse-adapted MARV exhibits many of the hallmarks of MARV disease in humans. By applying deep-sequencing to every passage of the virus, we are able to study virus evolution in this host with surprising precision. We show that two regions go through substantial changes: the intergenic region between NP and VP35, as well as the first 100 amino acids of the VP40 protein. Our results also reveal that there were profound changes during the production of the final virus stock in cell culture. Overall, our results show that a handful of regions carry most of the mutations acquired during the adaptation of the virus to a new host and that many mutations become fixed very early during the adaptation process.

Background Live-cell imaging is a powerful tool for visualization of the spatio-temporal dynamics of moving signals in living cells. Although this technique can be utilized to visualize nucleocapsid transport in Marburg virus (MARV)- or Ebola virus-infected cells, the experiments require biosafety level-4 (BSL-4) laboratories, which are restricted to trained and authorized individuals. Methods To overcome this limitation, we developed a live-cell imaging system to visualize MARV nucleocapsid-like structures using fluorescence-conjugated viral proteins, which can be conducted outside BSL-4 laboratories. Results Our experiments revealed that nucleocapsid-like structures have similar transport characteristics to those of nucleocapsids observed in MARV-infected cells, both of which are mediated by actin polymerization. Conclusions We developed a non-infectious live cell imaging system to visualize intracellular transport of MARV nucleocapsid-like structures. This system provides a safe platform to evaluate antiviral drugs that inhibit MARV nucleocapsid transport.

The filovirus plaque assay serves as the assay of choice to measure infectious virus in a cell culture, blood, or homogenized tissue sample. It has been in use for more than 30 years and is the generally accepted assay used to titrate virus in samples from animals treated with a potential antiviral therapeutic or vaccine. As these animal studies are required for the development of vaccines and therapeutics under the FDA Animal Rule, it is essential to have a standardized assay to compare their efficacies against the various filoviruses. Here, we present an evaluation of the conditions under which the filovirus plaque assay performs best for the Ebola virus Kikwit variant and the Angola variant of Marburg virus. The indicator cell type and source, inoculum volumes, length of incubation and general features of filovirus biology as visualized in the assay are addressed in terms of the impact on the sample viral titer calculations. These optimization studies have resulted in a plaque assay protocol which can be used for preclinical studies, and as a standardized protocol for use across institutions, to aid in data comparison. This protocol will be validated for use in GLP studies supporting advanced development of filovirus therapeutics and vaccines.

The fruit bat species Rousettus aegyptiacus was identified as a potential reservoir for the highly pathogenic filovirus Marburg virus. To establish a basis for a molecular understanding of the biology of filoviruses in the reservoir host, we have adapted a set of molecular tools for investigation of filovirus replication in a recently developed cell line, R06E, derived from the species Rousettus aegyptiacus. Upon infection with Ebola or Marburg viruses, R06E cells produced viral titers comparable to VeroE6 cells, as shown by TCID(50) analysis. Electron microscopic analysis of infected cells revealed morphological signs of filovirus infection as described for human- and monkey-derived cell lines. Using R06E cells, we detected an unusually high amount of intracellular viral proteins, which correlated with the accumulation of high numbers of filoviral nucleocapsids in the cytoplasm. We established protocols to produce Marburg infectious virus-like particles from R06E cells, which were then used to infect naïve target cells to investigate primary transcription. This was not possible with other cell lines previously tested. Moreover, we established protocols to reliably rescue recombinant Marburg viruses from R06E cells. These data indicated that R06E cells are highly suitable to investigate the biology of filoviruses in cells derived from their presumed reservoir.

Virus budding from the basolateral domain of infected polarized cells could be one of the mechanisms underlying the quick systemic infection induced by Marburg virus (MARV). We found that MARV buds from the basolateral pole of hepatocytes and bile epithelial cells in infected guinea pigs, which leads to the release of infectious virus into the vascular system. Basolateral budding might be orchestrated by the basolaterally located MARV matrix protein VP40, which induces a partial relocalization of MARV glycoprotein from the apical to the basolateral plasma membrane. This redistribution is a prerequisite for budding of infectious virions from the basolateral domain.

Viruses regulate cellular signalling pathways to ensure optimal viral replication. During Marburg virus (MARV) infection, large quantities of the viral glycoprotein GP are produced in the ER; this may result in the activation of the unfolded protein response (UPR). The most conserved pathway to trigger UPR is initiated by IRE1. Activation of IRE1 results in auto-phosphorylation, splicing of the XBP1 mRNA and translation of the XBP1s protein. XBP1s binds cis-acting UPR elements (UPRE) which leads to the enhanced expression of genes which should restore ER homeostasis. XBP1u protein is translated, if IRE1 is not activated. Here we show that ectopic expression of MARV GP activated the IRE1-XBP1 axis of UPR as monitored by UPRE luciferase assays. However, while at 24 h of infection with MARV IRE1 was phosphorylated, expression of XBP1s was only slightly enhanced and UPRE activity was not detected. The IRE1-XBP1 axis was not active at 48 h p.i. Co-expression studies of MARV proteins demonstrated that the MARV protein VP30 suppressed UPRE activation. Co-immunoprecipitation analyses revealed an RNA-dependent interaction of VP30 with XBP1u. Knock-out of IRE1 supported MARV infection at late time points. Taken together, these results suggest that efficient MARV propagation requires specific regulation of IRE1 activity.

Marburg and virulent Ebola viruses are maintained in hosts that are rare and have little contact with humans or do not readily transmit virus. Bats (particularly solitary microchiropteran species) are leading contenders as reservoir hosts. Virus transfer to humans occurs by contact with the primary reservoir or via an intermediate animal that acquired infection from the reservoir and is, in turn, hunted by humans. An interesting possibility is that filoviruses may be arthropod or plant viruses, with non—blood-feeding arthropods transmitting the virus to intermediate hosts or humans during oral ingestion or envenomation. Paradoxically, in Africa, Ebola virus disease has high lethality and high seroprevalence as determined by the IFA test. If the seroreactivity is confirmed by more specific tests, then the Ebola virus serogroup in Africa probably contains an antigenically cross-reactive, enzootic, nonpathogenic agent(s). Such viruses may have separate life cycles or may give rise to virulent strains by mutation.

The COVID-19 pandemic has not only strained healthcare systems in Africa but has also intensified the impact of emerging and re-emerging diseases. Specifically in Equatorial Guinea, mirroring the situation in other African countries, unique zoonotic outbreaks have occurred during this challenging period. One notable resurgence is Marburg virus disease (MVD), which has further burdened the already fragile healthcare system. The re-emergence of the Marburg virus amid the COVID-19 pandemic is believed to stem from a probable zoonotic spill-over, although the precise transmission routes remain uncertain. Given the gravity of the situation, addressing the existing challenges is paramount. Though the genome sequences from the current outbreak were not available for this study, we analyzed all the available whole genome sequences of this re-emerging pathogen to advocate for a shift towards active surveillance. This is essential to ensure the successful containment of any potential Marburg virus outbreak in Equatorial Guinea and the wider African context. This study, which presents an update on the phylodynamics and the genetic variability of MARV, further confirmed the existence of at least two distinct patterns of viral spread. One pattern demonstrates a slower but continuous and recurring virus circulation, while the other exhibits a faster yet limited and episodic spread. These results highlight the critical need to strengthen genomic surveillance in the region to effectively curb the pathogen’s dissemination. Moreover, the study emphasizes the importance of prompt alert management, comprehensive case investigation and analysis, contact tracing, and active case searching. These steps are vital to support the healthcare system’s response to this emerging health crisis. By implementing these strategies, we can better arm ourselves against the challenges posed by the resurgence of the Marburg virus and other infectious diseases.