[Show abstract][Hide abstract] ABSTRACT: Marburg virus (MARV), a zoonotic pathogen causing severe hemorrhagic fever in man, has emerged in Angola resulting in the largest outbreak of Marburg hemorrhagic fever (MHF) with the highest case fatality rate to date.
A mobile laboratory unit (MLU) was deployed as part of the World Health Organization outbreak response. Utilizing quantitative real-time PCR assays, this laboratory provided specific MARV diagnostics in Uige, the epicentre of the outbreak. The MLU operated over a period of 88 days and tested 620 specimens from 388 individuals. Specimens included mainly oral swabs and EDTA blood. Following establishing on site, the MLU operation allowed a diagnostic response in <4 hours from sample receiving. Most cases were found among females in the child-bearing age and in children less than five years of age. The outbreak had a high number of paediatric cases and breastfeeding may have been a factor in MARV transmission as indicated by the epidemiology and MARV positive breast milk specimens. Oral swabs were a useful alternative specimen source to whole blood/serum allowing testing of patients in circumstances of resistance to invasive procedures but limited diagnostic testing to molecular approaches. There was a high concordance in test results between the MLU and the reference laboratory in Luanda operated by the US Centers for Disease Control and Prevention.
The MLU was an important outbreak response asset providing support in patient management and epidemiological surveillance. Field laboratory capacity should be expanded and made an essential part of any future outbreak investigation.
[Show abstract][Hide abstract] ABSTRACT: The lectin DC-SIGN (dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin) augments Ebola virus (EBOV) infection. However, it its unclear whether DC-SIGN promotes only EBOV attachment (attachment factor function, nonessential) or actively facilitates EBOV entry (receptor function, essential).
We investigated whether DC-SIGN on B cell lines and dendritic cells acts as an EBOV attachment factor or receptor.
Engineered DC-SIGN expression rendered some B cell lines susceptible to EBOV glycoprotein (EBOV GP)-driven infection, whereas others remained refractory, suggesting that cellular factors other than DC-SIGN are also required for susceptibility to EBOV infection. Augmentation of entry was independent of efficient DC-SIGN internalization and might not involve lectin-mediated endocytic uptake of virions. Therefore, DC-SIGN is unlikely to function as an EBOV receptor on B cell lines; instead, it might concentrate virions onto cells, thereby allowing entry into cell lines expressing low levels of endogenous receptor(s). Indeed, artificial concentration of virions onto cells mirrored DC-SIGN expression, confirming that optimization of viral attachment is sufficient for EBOV GP-driven entry into some B cell lines. Finally, EBOV infection of dendritic cells was only partially dependent on mannose-specific lectins, such as DC-SIGN, suggesting an important contribution of other factors.
Our results indicate that DC-SIGN is not an EBOV receptor but, rather, is an attachment-promoting factor that boosts entry into B cell lines susceptible to low levels of EBOV GP-mediated infection.
No preview · Article · Dec 2007 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: The zinc finger antiviral protein (ZAP) was recently shown to inhibit Moloney murine leukemia virus and Sindbis virus replication. We tested whether ZAP also acts against Ebola virus (EBOV) and Marburg virus (MARV). Antiviral effects were observed after infection of cells expressing the N-terminal part of ZAP fused to the product of the zeocin resistance gene (NZAP-Zeo) as well as after infection of cells inducibly expressing full-length ZAP. EBOV was inhibited by up to 4 log units, whereas MARV was inhibited between 1 to 2 log units. The activity of ZAP was dependent on the integrity of the second and fourth zinc finger motif, as tested with cell lines expressing NZAP-Zeo mutants. Heterologous expression of EBOV- and MARV-specific sequences fused to a reporter gene suggest that ZAP specifically targets L gene sequences. The activity of NZAP-Zeo in this assay was also dependent on the integrity of the second and fourth zinc finger motif. Time-course experiments with infectious EBOV showed that ZAP reduces the level of L mRNA before the level of genomic or antigenomic RNA is affected. Transient expression of ZAP decreased the activity of an EBOV replicon system by up to 95%. This inhibitory effect could be partially compensated for by overexpression of L protein. In conclusion, the data demonstrate that ZAP exhibits antiviral activity against filoviruses, presumably by decreasing the level of viral mRNA.
Full-text · Article · Apr 2007 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: The nucleoprotein (NP) of Marburg virus (MARV) is responsible for the encapsidation of viral genomic RNA and the formation of the helical nucleocapsid precursors that accumulate in intracellular inclusions in infected cells. To form the large helical MARV nucleocapsid, NP needs to interact with itself and the viral proteins VP30, VP35 and L, which are also part of the MARV nucleocapsid. In the present study, a conserved coiled coil motif in the central part of MARV NP was shown to be an important element for the interactions of NP with itself and VP35, the viral polymerase cofactor. Additionally, the coiled coil motif was essential for the formation of NP-induced intracellular inclusions and for the function of NP in the process of transcription and replication of viral RNA in a minigenome system. Transfer of the coiled coil motif to a reporter protein was sufficient to mediate interaction of the constructed fusion protein with the N-terminus of NP. The coiled coil motif is bipartite, constituted by two coiled coils which are separated by a flexible linker.
[Show abstract][Hide abstract] ABSTRACT: The nucleocapsid protein VP35 of Marburgvirus, a filovirus, acts as the cofactor of the viral polymerase and plays an essential role in transcription and replication of the viral RNA. VP35 forms complexes with the genome encapsidating protein NP and with the RNA-dependent RNA polymerase L. In addition, a trimeric complex had been detected in which VP35 bridges L and the nucleoprotein NP. It has been presumed that the trimeric complex represents the active polymerase bound to the nucleocapsid. Here we present evidence that a predicted coiled-coil domain between amino acids 70 and 120 of VP35 is essential and sufficient to mediate homo-oligomerization of the protein. Substitution of leucine residues 90 and 104 abolished (i) the probability to form coiled coils, (ii) homo-oligomerization, and (iii) the function of VP35 in viral RNA synthesis. Further, it was found that homo-oligomerization-negative mutants of VP35 could not bind to L. Thus, it is presumed that homo-oligomerization-negative mutants of VP35 are unable to recruit the polymerase to the NP/RNA template. In contrast, inability to homo-oligomerize did not abolish the recruitment of VP35 into inclusion bodies, which contain nucleocapsid-like structures formed by NP. Finally, transcriptionally inactive mutants of VP35 containing the functional homo-oligomerization domain displayed a dominant-negative phenotype. Inhibition of VP35 oligomerization might therefore represent a suitable target for antiviral intervention.
Preview · Article · Jan 2006 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: The highly pathogenic enveloped Marburg virus (MARV) is composed of seven structural proteins and the nonsegmented negative-sense viral RNA genome. Four proteins (NP, VP35, VP30, and L) make up the helical nucleocapsid, which is surrounded by a matrix that is composed of the viral proteins VP40 and VP24. VP40 is functionally homologous to the matrix proteins of other nonsegmented negative-strand RNA viruses. As yet, the function of VP24 remains elusive. In the present study we found that VP24 colocalized with inclusions in MARV-infected cells that contain preformed nucleocapsids and with nucleocapsids outside the inclusions. Coexpression studies revealed that VP24 is recruited into the inclusions by the presence of NP. Furthermore, VP24 displayed membrane-binding properties and was recruited into filamentous virus-like particles (VLPs) that are induced by VP40. The incorporation of VP24 altered neither the morphology of VLPs nor the budding efficiency of VLPs. When VP24 was silenced in MARV-infected cells by small interfering RNA technology, the release of viral particles was significantly reduced while viral transcription and replication were unimpaired. Our data support the idea that VP24 is essential for a process that takes place after replication and transcription and before budding of virus progeny. It is presumed that VP24 is necessary for the formation of transport-competent nucleocapsids and/or the interaction between the nucleocapsids and the budding sites at the plasma membrane.
Preview · Article · Dec 2005 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Cellular attachment factors like the C-type lectins DC-SIGN and DC-SIGNR (collectively referred to as DC-SIGN/R) can augment viral infection and might promote viral dissemination in and between hosts. The lectin LSECtin is encoded in the same chromosomal locus as DC-SIGN/R and is coexpressed with DC-SIGNR on sinusoidal endothelial cells in liver and lymphnodes. Here, we show that LSECtin enhances infection driven by filovirus glycoproteins (GP) and the S protein of SARS coronavirus, but does not interact with human immunodeficiency virus type-1 and hepatitis C virus envelope proteins. Ligand binding to LSECtin was inhibited by EGTA but not by mannan, suggesting that LSECtin unlike DC-SIGN/R does not recognize high-mannose glycans on viral GPs. Finally, we demonstrate that LSECtin is N-linked glycosylated and that glycosylation is required for cell surface expression. In summary, we identified LSECtin as an attachment factor that in conjunction with DC-SIGNR might concentrate viral pathogens in liver and lymph nodes.
[Show abstract][Hide abstract] ABSTRACT: High mortality rates and lack of an available vaccine against Marburg haemorrhagic fever (MHF) highlight the need for a defensive therapy against MHF and greater knowledge of the causative agent, the Marburg virus (MARV). Here, RNA interference (RNAi) is employed to destroy MARV transcripts, disrupting replication and allowing analysis of various roles of MARV proteins. Small interfering RNAs (siRNAs) homologous to three MARV transcripts (NP, VP35 and VP30) were co-transfected into cells with plasmids encoding the corresponding nucleocapsid proteins. The resulting decrease in MARV nucleocapsid-protein levels was shown to be specific, as siRNA that was not homologous to the MARV genome did not decrease the levels of viral nucleocapsid proteins. Additionally, transcript levels of double-stranded RNA (dsRNA)-sensor proteins, the dsRNA-activated protein kinase and 2',5'-oligoadenylate synthetase 1 remained unchanged, suggesting that the decrease in viral proteins was not a result of activation of the antiviral properties of the interferon system. Subsequently, siRNAs were shown to reduce intracellular viral proteins in MARV-infected cells and viral material released into the medium. Targeted reduction of VP30 downregulated the intracellular levels of all other viral proteins, suggesting that VP30 plays an essential role for transcription/replication. The efficient reduction of MARV replication also suggests that RNAi may provide an agent against MHF.
Full-text · Article · May 2005 · Journal of General Virology
[Show abstract][Hide abstract] ABSTRACT: The lectins DC-SIGN and DC-SIGNR can augment viral infection; however, the range of pathogens interacting with these attachment
factors is incompletely defined. Here we show that DC-SIGN and DC-SIGNR enhance infection mediated by the glycoprotein (GP)
of Marburg virus (MARV) and the S protein of severe acute respiratory syndrome coronavirus and might promote viral dissemination.
SIGNR1, a murine DC-SIGN homologue, also enhanced infection driven by MARV and Ebola virus GP and could be targeted to assess
the role of attachment factors in filovirus infection in vivo.
Full-text · Article · Dec 2004 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Ebola virus (EBOV) causes severe outbreaks of Ebola hemorrhagic fever in endemic regions of Africa and is considered to be of impact for other parts of the world as an imported viral disease. To develop a new diagnostic test, monoclonal antibodies to EBOV were produced from mice immunized with inactivated EBOV species Zaire. Antibodies directed against the viral glycoprotein GP were characterized by ELISA, Western blot and immunofluorescence analyses. An antigen capture ELISA was established, which is specific for EBOV-Zaire and shows a sensitivity of approximately 10(3) plaque-forming units/ml. Since the ELISA is able to detect even SDS-inactivated EBOV in spiked human sera, it could complement the existing diagnostic tools in the field and in routine laboratories where high containment facilities are not available.
Preview · Article · Dec 2004 · Medical Microbiology and Immunology
[Show abstract][Hide abstract] ABSTRACT: Replication-competent recombinant vesicular stomatitis viruses (rVSVs) expressing the type I transmembrane glycoproteins and
selected soluble glycoproteins of several viral hemorrhagic fever agents (Marburg virus, Ebola virus, and Lassa virus) were
generated and characterized. All recombinant viruses exhibited rhabdovirus morphology and replicated cytolytically in tissue
culture. Unlike the rVSVs with an additional transcription unit expressing the soluble glycoproteins, the viruses carrying
the foreign transmembrane glycoproteins in replacement of the VSV glycoprotein were slightly attenuated in growth. Biosynthesis
and processing of the foreign glycoproteins were authentic, and the cell tropism was defined by the transmembrane glycoprotein.
None of the rVSVs displayed pathogenic potential in animals. The rVSV expressing the Zaire Ebola virus transmembrane glycoprotein
mediated protection in mice against a lethal Zaire Ebola virus challenge. Our data suggest that the recombinant VSV can be
used to study the role of the viral glycoproteins in virus replication, immune response, and pathogenesis.
Full-text · Article · Jun 2004 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Ebola virus (EBOV) causes uncommon but dramatic outbreaks in remote regions of Africa, where diagnostic facilities are limited. In order to develop diagnostic tests, which can be handled and distributed easily, monoclonal antibodies (mAbs) to EBOV, species Zaire, were produced from mice immunized with inactivated viral particles. Nine stable hybridoma cell lines were obtained producing specific mAbs directed against the viral structural protein VP40. These mAbs were characterized by enzyme-linked immunosorbent, immunoblot and immunofluorescence assays. Subsequently, an antigen capture enzyme-linked immunosorbent assay was established, which detects VP40 of all known species of EBOV. This assay could detect viral material in spiked human serum that has been sodium dodecylsulfate-inactivated. The established enzyme-linked immunosorbent assay therefore has the ability to become a very useful tool for obtaining an accurate diagnosis in the field, limiting the risk of laboratory infections.
No preview · Article · Aug 2003 · Journal of Virological Methods
[Show abstract][Hide abstract] ABSTRACT: Das Marburg-Virus verursacht eine fieberhafte hämorrhagische Erkrankung bei menschlichen und nichtmenschlichen Primaten, die mit hohen Letalitätsraten einhergeht. Taxonomisch bildet das Marburg-Virus (MARV) zusammen mit dem Ebola-Virus (EBOV) die Familie der Filoviridae. Die Virionen sind aus einem Nukleokapsidkomplex, der über eine Proteinmatrix mit der Virushülle verbunden ist, aufgebaut. Der Nukleokapsidkomplex besteht aus der viralen RNA sowie den vier Nukleokapsidproteinen NP, VP35, VP30 und L, die untereinander durch verschiedene Protein-Protein-Interaktionen verbunden sind. Der Komplex aus VP35 und dem L-Protein fungiert als virale RNA-abhängige RNA Polymerase, wobei L den katalytischen Teil des Enzyms darstellt. In der vorliegenden Arbeit wurde die Homooligomerisierung des Polymerasekofaktors VP35 des MARV hinsichtlich ihrer Funktion für die Synthese der viralen RNA und die Morphogenese neuer Nukleokapsidkomplexe sowie die Interaktion des VP35 mit dem NP untersucht. Die Homooligomerisierung des MARV VP35 wird über eine Coiled-Coil-Struktur im N-Terminus des Proteins vermittelt, die im Bereich der Aminosäuren 70 bis 120 lokalisiert ist. Zwei Leucinreste an den Positionen 90 und 104 waren ausschlaggebend für die Stabilität der Coiled-Coil-Struktur und somit für die Homooligomerisierung des VP35. Ferner konnte gezeigt werden, dass das Coiled-Coil-Motiv des VP35 ausreichend war, um die Protein-Protein-Interaktion zu vermitteln. Die Homooligomerisierung des VP35 bildete die Voraussetzung für die Interaktion mit dem L-Protein und die Ausbildung eines funktionellen Polymerasekomplexes. Im Gegensatz dazu schien die Homooligomerisierung des VP35 für die Bindung an das NP, der strukturgebenden Komponente des Nukleokapsidkomplexes, nicht notwendig zu sein. Über die Interaktion des NP mit dem N-Terminus des VP35 könnte das NP durch das VP35 in Lösung gehalten und während der Replikation der viralen RNA als Substrat für deren Verpackung zur Verfügung gestellt werden. Eine weitere NP-Bindungsstelle auf dem C-Terminus des VP35 scheint eine wichtige Rolle beim Zusammenbau neuer Nukleokapsidkomplexe zu spielen. Die Integrität der Coiled-Coil-Strukturen des VP35 und des NP hatte einen wesentlichen Einfluss auf die Ausbildung und die Struktur der intrazytoplasmatischen Einschlusskörper, die die Reifezentren neuer Nukleokapsidkomplexe darstellen. Zusammenfassend lässt sich festhalten, dass die Homooligomerisierung des MARV VP35 essentiell für dessen Interaktion mit dem L und für die virale Transkription und Replikation ist. Für die direkte Interaktion von VP35 mit NP scheint die Homooligomerisierung des VP35 keine Rolle zu spielen. Es zeichnet sich allerdings ab, dass für die Entstehung von funktionellen Nukleokapsiden die Homooligomerisierung des VP35 notwendig ist. Marburgvirus causes a fulminant hemorrhagic fever among humans and nonhuman primates with high fatality rates. Marburgvirus (MARV) and the closely related Ebolavirus (EBOV) together make up the family Filoviridae. The Marburgvirus particles are composed of a nucleocapsid complex, which is connected to the lipid envelope by a protein matrix. Nucleocapsids are constituted by the viral RNA genome and the four nucleocapsid proteins NP, VP35, VP30, and L, which are involved in the formation of different protein-protein complexes. The complex of VP35 and L represents the active RNA-dependent RNA polymerase, with VP35 serving as the polymerase cofactor. In the present study, we characterized the biological significance of homooligomerization of the polymerase cofactor VP35 for transcription and replication of viral RNA. Additionally, we focused on morphogenesis of new nucleocapsid complexes by investigation the interaction of VP35 and NP. A predicted coiled-coil domain between amino acids 70 and 120 of VP35 is essential and sufficient to mediate homooligomerization of the protein. Substitution of leucine residues 90 and 104 abolished (I) the probability to form coiled-coils, (II) homooligomerization, and (III) the function of VP35 in viral RNA synthesis. Furthermore it was found that homooligomerization of VP35 is a prerequisite for the binding of L. In contrast, inability to homooligomerize did not abolish the recruitment of VP35 into NP-induced inclusion bodies. These inclusions are presumed to represent centers of viral replication and formation of nucleocapsids. An N-terminal fragment of VP35 was found to keep NP in solution, which might be necessary to provide NP as substrate for encapsidation of newly synthesized RNA. In combination with the N-terminal binding site a second NP-binding site on VP35 was essential for the formation of typical inclusions. Homooligomers of VP35 were able to substitute a missing NP-NP self interaction site during formation of nucleocapsids. Together, the data presented that an N-terminal coiled-coil motif in VP35 is essential and sufficient for homooligomerization of the protein. While homooligomerization is dispensable for the recruitment of VP35 into the NP-induced inclusion bodies, it is essential for the function of the protein during replication and transcription since monomeric VP35 is not able to recruit the polymerase to the NP/RNA template.