Search

Zaire Ebolavirus (ZEBOV) continues to pose a significant threat to human health as highlighted by the recent epidemic that originated in West Africa and the ongoing outbreak in the Democratic Republic of the Congo. Although the ZEBOV variant responsible for this epidemic (Makona) shares significant genetic similarity with previously identified variants (Kikwit and Mayinga), recent reports suggest slower disease progression in nonhuman primates. However, the pathogenesis caused by the new variant is not fully understood. We present the first comprehensive approach in understanding ZEBOV-Makona pathogenesis in cynomolgus macaques by measuring changes in immune cell frequencies, plasma levels of immune mediators, and differentially expressed genes (DEGs) within whole blood (WB) and peripheral blood mononuclear cells (PBMC). Our combined approach revealed a link between: 1) increased interferon-stimulated gene expression, IFNα levels, and activated plasmacytoid dendritic cells; 2) higher proinflammatory gene expression, cytokine and chemokine levels, and non-classical monocytes; 3) gene signature of leukocyte activation and increased granulocytes; and 4) decreased expression of lymphocyte related genes and lymphopenia. In addition, our data strongly indicate delayed disease progression as well as limited overlap (~30%) in host transcriptome changes following ZEBOV-Makona infection compared to ZEBOV-Kikwit. These observations provide novel insight into the molecular mechanisms of ZEBOV-Makona pathogenesis.

Background: Rodent models that accurately reflect human filovirus infection are needed as early screens for medical countermeasures. Prior work in rodents with the Zaire species of Ebola virus (ZEBOV) primarily used inbred mice and guinea pigs to model disease. However, these inbred species do not show some of the important features of primate ZEBOV infection, most notably, coagulation abnormalities., Methods: Thirty-six outbred guinea pigs were infected with guinea pig-adapted ZEBOV and examined sequentially over an 8-day period to investigate the pathologic events that lead to death., Results: Features of disease in ZEBOV-infected outbred guinea pigs were largely consistent with disease in humans and nonhuman primates and included early infection of macrophages and dendritiform cells, apoptosis of bystander lymphocytes, and increases in levels of proinflammatory cytokines. Most importantly, dysregulation of circulating levels of fibrinogen, protein C activity, and antifibrinolytic proteins and deposition of fibrin in tissues demonstrated both biochemical and microscopic evidence of disseminated intravascular coagulation., Conclusions: These findings suggest that the outbred guinea pig model recapitulates ZEBOV infection of primates better than inbred rodent models, is useful for dissecting key events in the pathogenesis of ZEBOV, and is useful for evaluating candidate interventions prior to assessment in primates., (© The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

The family Filoviridae contains three genera, Ebolavirus (EBOV), Marburg virus, and Cuevavirus. Some members of the EBOV genus, including Zaire ebolavirus (ZEBOV), can cause lethal haemorrhagic fever in humans. During 2014 an unprecedented ZEBOV outbreak occurred in West Africa and is still ongoing, resulting in over 10,000 deaths, and causing global concern of uncontrolled disease. To meet this challenge a rapid-acting vaccine is needed. Many vaccine approaches have shown promise in being able to protect nonhuman primates against ZEBOV. In response to the current ZEBOV outbreak several of these vaccines have been fast tracked for human use. However, it is not known whether any of these vaccines can provide protection against the new outbreak Makona strain of ZEBOV. One of these approaches is a first-generation recombinant vesicular stomatitis virus (rVSV)-based vaccine expressing the ZEBOV glycoprotein (GP) (rVSV/ZEBOV). To address safety concerns associated with this vector, we developed two candidate, further-attenuated rVSV/ZEBOV vaccines. Both attenuated vaccines produced an approximately tenfold lower vaccine-associated viraemia compared to the first-generation vaccine and both provided complete, single-dose protection of macaques from lethal challenge with the Makona outbreak strain of ZEBOV.

Zaire Ebola virus infection in macaques causes a fatal disease with a pathogenesis similar to that in humans. During several independent therapy studies, we noted altered tissue tropism in 6 rhesus macaques that survived longer than those with a typical disease course. The mean time to death for these 6 macaques was 21.7 days, which is significantly longer than the average mean time to death of 8.3 days for 20 untreated historical control animals. In addition to living significantly longer, these 6 animals exhibited a variety of deteriorating clinical signs with pathologic findings that were not seen in the untreated control animals, as well as the presence of viral antigen in the brain, eye, pancreas, thyroid, and lung. We suggest that treatment extended the time course of the disease and permitted the virus to infect tissues not usually affected in the typical model.

To facilitate an understanding of the molecular aspects of the pathogenesis of Zaire ebolavirus (ZEBOV) infection, we generated 2 different recombinant viruses expressing enhanced green fluorescent protein (eGFP) from additional transcription units inserted at different positions in the virus genome. These viruses showed in vitro phenotypes similar to that of wild-type ZEBOV (wt-ZEBOV) and were stable over multiple passages. Infection with one of the viruses expressing eGFP produced only mild disease in rhesus macaques, demonstrating a marked attenuation in this animal model. However, in mice lacking signal transducer and activator of transcription 1, both viruses expressing eGFP caused lethal cases of disease that were moderately attenuated, compared with that caused by wt-ZEBOV. In mice, viral replication could be easily tracked by the detection of eGFP-positive cells in tissues, by use of flow cytometry. These findings demonstrate that the incorporation of a foreign gene will attenuate ZEBOV in vivo but that these viruses still have potential for in vitro and in vivo research applications.

Marburg (MARV) and Ebola viruses (EBOV) emerged from the rainforests of Central Africa more than 30 years ago causing outbreaks of severe and, usually, fatal hemorrhagic fever. EBOV has garnered the lion's share of the attention, fueled by the higher frequency of EBOV outbreaks, high mortality rates and importation into the USA, documented in such popular works as the best-selling novel 'The Hot Zone'. However, recent large outbreaks of hundreds of cases of MARV infection in the Democratic Republic of the Congo and Angola with case fatalities approaching 90% dramatically highlight its lethal potential. Although no vaccines or antiviral drugs for MARV are currently available, remarkable progress has been made over the last few years in developing potential countermeasures against MARV in nonhuman primate models. In particular, a vaccine based on attenuated recombinant vesicular stomatitis virus was recently shown to have both preventive and postexposure efficacy.