Distinct Biological Phenotypes of Marburg and Ravn Virus Infection in Macaques.

Filoviruses are among the most pathogenic infectious agents known to human, with high destructive potential, as evidenced by the recent Ebola virus epidemic in West Africa. As members of the filovirus family, marburgviruses have caused similar devastating outbreaks, albeit with lower case numbers. In this study we compare the pathogenesis of Ravn virus (RAVV) and Marburg virus (MARV) strains Angola, Musoke, and Ozolin in rhesus and cynomolgus macaques, the 2 nonhuman primate species most commonly used in filovirus research. Our results reveal the most pathogenic MARV strain to be Angola, followed by Musoke, whereas Ozolin is the least pathogenic. We also demonstrate that RAVV is highly pathogenic in cynomolgus macaques but less pathogenic in rhesus macaques. Our results demonstrate a preferential infection of endothelial cells by MARVs; in addition, analysis of tissue samples suggests that lymphocyte and hepatocyte apoptosis might play a role in MARV pathogenicity. This information expands our knowledge about pathogenicity and virulence of marburgviruses.

Infection Rates and Risk Factors for Infection Among Health Workers During Ebola and Marburg Virus Outbreaks: A Systematic Review.

Background: Infection in health workers (HWs) has characterized outbreaks of Ebola virus disease (EVD) and Marburg virus disease (MVD). We conducted a systematic review to investigate infection and mortality rates and common exposure risks in HWs in EVD and MVD outbreaks. Methods: We searched the EMBASE and PubMed databases to identify articles posted before 27 December 2017, with no language restrictions. Data on the number, frequency, and mortality of HW infection and exposure risks were extracted. Results: Ninety-four articles related to 22 outbreaks were included. HW infections composed 2%-100% of cases in EVD and 5%-50% of cases in MVD outbreaks. Among exposed HWs, 0.6%-92% developed EVD, and 1%-10% developed MVD. HW infection rates were consistent through outbreaks. The most common exposure risk situations were inadequate personal protective equipment and exposure to patients with unrecognized EVD/MVD. Similar risks were reported in past EVD/MVD outbreaks and in the recent outbreak in West Africa. Conclusions: Many outbreaks reported high proportions of infected HWs. Similar HW infection rates and exposure risk factors in both past and recent EVD and MVD outbreaks emphasize the need to improve the implementation of appropriate infection control measures consistently across all healthcare settings.

Natural History and Pathogenesis of Wild-Type Marburg Virus Infection in STAT2 Knockout Hamsters.

Marburg virus (MARV; family Filoviridae) causes sporadic outbreaks of Marburg hemorrhagic fever in sub-Saharan Africa with case fatality rates reaching 90%. Wild-type filoviruses, including MARV and the closely related Ebola virus, are unable to suppress the type I interferon response in rodents, and therefore require adaptation of the viruses to cause disease in immunocompetent animals. In the current study, we demonstrate that STAT2 knockout Syrian hamsters are susceptible to infection with different wild-type MARV variants. MARV Musoke causes a robust and systemic infection resulting in lethal disease. Histopathological findings share features similar to those observed in human patients and other animal models of filovirus infection. Reverse-transcription polymerase chain reaction analysis of host transcripts shows a dysregulation of the innate immune response. Our results demonstrate that the STAT2 knockout hamster represents a novel small animal model of severe MARV infection and disease without the requirement for virus adaptation.

Animal models for filovirus infections.

The family Filoviridae, which includes the genera Marburgvirus and Ebolavirus, contains some of the most pathogenic viruses in humans and non-human primates (NHPs), causing severe hemorrhagic fevers with high fatality rates. Small animal models against filoviruses using mice, guinea pigs, hamsters, and ferrets have been developed with the goal of screening candidate vaccines and antivirals, before testing in the gold standard NHP models. In this review, we summarize the different animal models used to understand filovirus pathogenesis, and discuss the advantages and disadvantages of each model with respect to filovirus disease research.

Development and characterization of a guinea pig model for Marburg virus.

The Angolan strain of Marburg virus (MARV/Ang) can cause lethal disease in humans with a case fatality rate of up to 90%, but infection of immunocompetent rodents do not result in any observable symptoms. Our previous work includes the development and characterization of a MARV/Ang variant that can cause lethal disease in mice (MARV/Ang-MA), with the aim of using this tool to screen for promising prophylactic and therapeutic candidates. An intermediate animal model is needed to confirm any findings from mice studies before testing in the gold-standard non-human primate (NHP) model. In this study, we serially passaged the clinical isolate of MARV/Ang in the livers and spleens of guinea pigs until a variant emerged that causes 100% lethality in guinea pigs (MARV/Ang-GA). Animals infected with MARV/Ang-GA showed signs of filovirus infection including lymphocytopenia, thrombocytopenia, and high viremia leading to spread to major organs, including the liver, spleen, lungs, and kidneys. The MARV/Ang-GA guinea pigs died between 7-9 days after infection, and the LD50 was calculated to be 1.1×10-1 TCID50 (median tissue culture infective dose). Mutations in MARV/Ang-GA were identified and compared to sequences of known rodent-adapted MARV/Ang variants, which may benefit future studies characterizing important host adaptation sites in the MARV/Ang viral genome.

Filovirus pathogenesis and immune evasion: insights from Ebola virus and Marburg virus.

Ebola viruses and Marburg viruses, members of the filovirus family, are zoonotic pathogens that cause severe disease in people, as highlighted by the latest Ebola virus epidemic in West Africa. Filovirus disease is characterized by uncontrolled virus replication and the activation of host responses that contribute to pathogenesis. Underlying these phenomena is the potent suppression of host innate antiviral responses, particularly the type I interferon response, by viral proteins, which allows high levels of viral replication. In this Review, we describe the mechanisms used by filoviruses to block host innate immunity and discuss the links between immune evasion and filovirus pathogenesis.

Structural basis for Marburg virus VP35-mediated immune evasion mechanisms.

Filoviruses, marburgvirus (MARV) and ebolavirus (EBOV), are causative agents of highly lethal hemorrhagic fever in humans. MARV and EBOV share a common genome organization but show important differences in replication complex formation, cell entry, host tropism, transcriptional regulation, and immune evasion. Multifunctional filoviral viral protein (VP) 35 proteins inhibit innate immune responses. Recent studies suggest double-stranded (ds)RNA sequestration is a potential mechanism that allows EBOV VP35 to antagonize retinoic-acid inducible gene-I (RIG-I) like receptors (RLRs) that are activated by viral pathogen-associated molecular patterns (PAMPs), such as double-strandedness and dsRNA blunt ends. Here, we show that MARV VP35 can inhibit IFN production at multiple steps in the signaling pathways downstream of RLRs. The crystal structure of MARV VP35 IID in complex with 18-bp dsRNA reveals that despite the similar protein fold as EBOV VP35 IID, MARV VP35 IID interacts with the dsRNA backbone and not with blunt ends. Functional studies show that MARV VP35 can inhibit dsRNA-dependent RLR activation and interferon (IFN) regulatory factor 3 (IRF3) phosphorylation by IFN kinases TRAF family member-associated NFkb activator (TANK) binding kinase-1 (TBK-1) and IFN kB kinase e (IKKe) in cell-based studies. We also show that MARV VP35 can only inhibit RIG-I and melanoma differentiation associated gene 5 (MDA5) activation by double strandedness of RNA PAMPs (coating backbone) but is unable to inhibit activation of RLRs by dsRNA blunt ends (end capping). In contrast, EBOV VP35 can inhibit activation by both PAMPs. Insights on differential PAMP recognition and inhibition of IFN induction by a similar filoviral VP35 fold, as shown here, reveal the structural and functional plasticity of a highly conserved virulence factor.

Pathogenesis of Marburg hemorrhagic fever in cynomolgus macaques.

BACKGROUND: Marburg virus (MARV) infection causes a severe and often fatal hemorrhagic disease in primates; however, little is known about the development of MARV hemorrhagic fever. In this study we evaluated the progression of MARV infection in nonhuman primates. METHODS: Eighteen cynomolgus monkeys were infected with MARV; blood and tissues were examined sequentially over an 8-day period to investigate disease pathogenesis. RESULTS: Disease caused by MARV in cynomolgus macaques was very similar to disease previously described for Ebola virus-infected macaques. Monocytes, macrophages, Kupffer cells, and dendritic cells (DCs) were identified as the initial targets of MARV infection. Bystander lymphocyte apoptosis occurred at early stages in the disease course in intravascular and extravascular locations. The loss of splenic and lymph node DCs or downregulation of dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) on DCs as early as day 2 and continuing through day 8 after MARV infection was a prominent finding. Evidence of disseminated intravascular coagulation was noted; however, the degree of fibrin deposition in tissues was less prominent than was reported in Ebola-infected macaques. CONCLUSIONS: The sequence of pathogenic events identified in this study provides an understanding of the development of disease processes and also may provide new targets for rational prophylactic and chemotherapeutic interventions.

Ebola and marburg hemorrhagic fever.

Ebola and Marburg viruses cause a severe viral hemorrhagic fever disease mainly in Sub-Saharan Africa. Although outbreaks are sporadic, there is the potential for filoviruses to spread to other continents unintentionally because of air travel or intentionally because of bioterrorism. This article discusses the natural history, epidemiology, and clinical presentation of patients infected with Ebola and Marburg viruses. Clinicians in the United States should be aware of the symptoms of these viral infections in humans and know the appropriate procedures for contacting local, state, and national reference laboratories in the event of a suspected case of filoviral hemorrhagic fever.

Pathogenesis of filoviral haemorrhagic fevers.

The filoviruses, marburgvirus and ebolavirus, cause epidemics of haemorrhagic fever with high case-fatality rates. The severe illness results from a complex of pathogenetic mechanisms that enable the virus to suppress innate and adaptive immune responses, infect and kill a broad variety of cell types, and elicit strong inflammatory responses and disseminated intravascular coagulation, producing a syndrome resembling septic shock. Most experimental data have been obtained on Zaire ebolavirus, which causes uniformly lethal disease in experimentally infected non-human primates but produces a broader range of outcomes in naturally infected human beings. 10-30% of patients can survive the illness by mobilising adaptive immune responses, and there is limited evidence that mild or symptomless infections also occur. The other filoviruses that have caused human disease, Sudan ebolavirus, Ivory Coast ebolavirus, and marburgvirus, produce a similar illness but with somewhat lower case-fatality rates. Variations in outcome during an epidemic might be due partly to genetically determined differences in innate immune responses to the viruses. Recent studies in non-human primates have shown that blocking of certain host responses, such as the coagulation cascade, can result in reduced viral replication and improved host survival.

[Democratic Republic of the Congo: between civil war and the Marburg virus. International Committee of Technical and Scientific Coordination of the Durba Epidemic]. / République Démocratique du Congo: entre guerre civile et virus Marburg. Comite International de Coordination Technique et Scientifique de l'Epidemie de Durba.

Because the epidemiology of viral hemorrhagic fever is unclear, each outbreak is a spectacular event that focuses the attention of the international scientific community. When an epidemic of Marburg virus disease occurred in the Durba region located in the northeastern part of the People's Republic of the Congo, 23 scientists were sent from 12 different countries. Sixty of the 73 people infected died. The first case was observed in December 1998 and the last in May 1999. Because of political unrest in the country, the outbreak was not reported immediately and most data was collected by observers retrospectively. However Marburg virus infection was confirmed in 5 of 16 patients in whom testing was performed and person-to-person transmission was demonstrated. Thus the Durba outbreak was the first epidemic of Marburg virus disease not involving laboratory contamination. Initial epidemiologic findings suggest that the first cases involved miners who were probably infected by contact with an animal reservoir such as bats. Further studies to determine seroprevalence in the general population and virologic testing on animals captured in the zone should provide answers to these questions.

[The effect of the methods for producing an experimental Marburg virus infection on the characteristics of the course of the disease in green monkeys]. / Vliianie sposobov éksperimental'nogo zarazheniia virusom Marburg na osobennosti protekaniia bolezni u zelenykh martyshek.

A comparative study on the features of the pathogenesis of Marburg disease after parenteral and aerosol infection of green monkeys with a virus prepared from native culture suspension and that after lyophilization was carried out. The changes in the dynamics of the clotting time, the activity of serum aminotransferases, the duration of prefebrile period and survival time were analysed in different cases. No lethality was observed in animals infected with small doses of aerosol preparations.

Exotic viral diseases.

Marburg virus disease, Lassa fever, monkeypox, and Ebola virus diseases of humans have all been recognized since 1967. These are examples of some of the exotic virus diseases which through importation may present a potential public health problem in the United States. Some of these viruses are also highly hazardous to laboratory and medical personnel. This paper is a review of the general characteristics, the epidemiology, and laboratory diagnosis of the exotic viruses which have been described during the last 25 years.