Evidence for occurrence of filovirus antibodies in humans and imported monkeys: do subclinical filovirus infections occur worldwide?

Marburg virus disease outbreaks, mathematical models, and disease parameters: a systematic review

The 2023 Marburg virus disease outbreaks in Equatorial Guinea and Tanzania highlighted the importance of better understanding this lethal pathogen. We did a systematic review (PROSPERO CRD42023393345) of peer-reviewed articles reporting historical outbreaks, modelling studies, and epidemiological parameters focused on Marburg virus disease. We searched PubMed and Web of Science from database inception to March 31, 2023. Two reviewers evaluated all titles and abstracts with consensus-based decision making. To ensure agreement, 13 (31%) of 42 studies were double-extracted and a custom-designed quality assessment questionnaire was used for risk of bias assessment. We present detailed information on 478 reported cases and 385 deaths from Marburg virus disease. Analysis of historical outbreaks and seroprevalence estimates suggests the possibility of undetected Marburg virus disease outbreaks, asymptomatic transmission, or cross-reactivity with other pathogens, or a combination of these. Only one study presented a mathematical model of Marburg virus transmission. We estimate an unadjusted, pooled total random effect case fatality ratio of 61·9% (95% CI 38·8-80·6; I2=93%). We identify epidemiological parameters relating to transmission and natural history, for which there are few estimates. This systematic review and the accompanying database provide a comprehensive overview of Marburg virus disease epidemiology and identify key knowledge gaps, contributing crucial information for mathematical models to support future Marburg virus disease epidemic responses.

Ebola-Detect: A differential serodiagnostic assay for Ebola virus infections and surveillance in the presence of vaccine-induced antibodies

Background

Ebola virus (EBOV) vaccines containing glycoprotein (GP) provide protection against severe Ebola virus disease (EVD). EBO vaccinations elicit antibodies that are detectable in Ebola serodiagnostic tests, as EBOV GP is a major target antigen. This vaccine-induced seropositivity presents issues with early detection of natural EBOV infections, following vaccination and during surveillance, leading to ‘uninfected’ vaccine trial participants being falsely diagnosed as ‘EBOV infected’ potentially resulting in long-term social and economic distress. Since mass vaccinations are being employed to curtail the recurrent EBOV epidemics in multiple African countries, it is, therefore, essential to differentiate vaccine-induced from natural infection–induced antibodies by a differential serodiagnosis assay for accurate detection of Ebola virus infections.

Methods

To develop a serodiagnostic test that can differentiate between individuals with EBOV infection-induced antibodies and individuals with EBOV vaccine-induced antibodies, we analysed peptides of EBOV viral protein 40 (VP40), viral protein 35 (VP35) and nucleocapsid protein (NP) using an ELISA with a panel of 181 human sera collected from healthy controls, EBO vaccinees, and EBOV-infected survivors. Receiver Operating Characteristic (ROC) curve analysis was used to calculate sensitivity and specificity of the assay. A simple peptide-based serodiagnostic assay was used to evaluate detection of breakthrough EBOV infections in vaccinated non-human primates (NHP) in EBOV challenge studies.

Findings

We identified conserved peptide sequences in EBOV VP40, VP35 and NP, produced soon after EBOV infection that are not part of the current EBO vaccine target antigens. The new ELISA-based differential serodetection assay termed ‘EBOV-Detect’ demonstrated >94% specificity and 96% sensitivity for diagnosis of EBOV infection. Importantly, the uninfected vaccine-trial participants scored negative in ‘EBOV-Detect’ assay. The results from the NHPs EBOV challenge study established that post-EBO vaccination serum scored negative in ‘EBOV-Detect’ and all NHPs with Ebola breakthrough infections, following EBOV challenge, were serodiagnosed positively with EBOV-Detect.

Interpretation

The new ‘EBOV-Detect’ is a simple and sensitive serodiagnostic assay that can specifically differentiate between natural Ebola virus infected and those with vaccine-induced immunity. This could potentially be implemented as a robust diagnostic tool for epidemiology and surveillance of EBOV infections during and after outbreaks, especially in countries with mass Ebola vaccinations.

Funding

The antibody characterization work described in this manuscript was supported by FDA Office of Counterterrorism and Emerging Threats (OCET) - Medical Countermeasures initiative (MCMi) grant- OCET 2019-1018 and Defense Threat Reduction Agency (HDTRA1930447) funds to S.K.

Longitudinal antibody and T cell responses in Ebola virus disease survivors and contacts: an observational cohort study

BACKGROUND

The 2013-16 Ebola virus disease epidemic in west Africa caused international alarm due to its rapid and extensive spread resulting in a significant death toll and social unrest within the affected region. The large number of cases provided an opportunity to study the long-term kinetics of Zaire ebolavirus-specific immune response of survivors in addition to known contacts of those infected with the virus.

METHODS

In this observational cohort study, we worked with leaders of Ebola virus disease survivor associations in two regions of Guinea, Guéckédou and Coyah, to recruit survivors of Ebola virus disease, contacts from households of individuals known to have had Ebola virus disease, and individuals who were not knowingly associated with infected individuals or had not had Ebola virus disease symptoms to serve as negative controls. We did Zaire ebolavirus glycoprotein-specific T cell analysis on peripheral blood mononuclear cells (PBMCs) on location in Guinea and transported plasma and PBMCs back to Europe for antibody quantification by ELISA, functional neutralising antibody analysis using live Zaire ebolavirus, and T cell phenotype studies. We report on the longitudinal cellular and humoral response among Ebola virus disease survivors and highlight potentially paucisymptomatic infection.

FINDINGS

We recruited 117 survivors of Ebola virus disease, 66 contacts, and 23 negative controls. The mean neutralising antibody titre among the Ebola virus disease survivors 3-14 months after infection was 1/174 (95% CI 1/136-1/223). Individual results varied greatly from 1/10 to more than 1/1000 but were on average ten times greater than that induced after 1 month by single dose Ebola virus vaccines. Following reactivation with glycoprotein peptide, the mean T cell responses among 116 Ebola virus disease survivors as measured by ELISpot was 305 spot-forming units (95% CI 257-353). The dominant CD8+ polyfunctional T cell phenotype, as measured among 53 Ebola virus disease survivors, was interferon γ+, tumour necrosis factor+, interleukin-2-, and the mean response was 0·046% of total CD8+ T cells (95% CI 0·021-0·071). Additionally, both neutralising antibody and T cell responses were detected in six (9%) of 66 Ebola virus disease contacts. We also noted that four (3%) of 117 individuals with Ebola virus disease infections did not have circulating Ebola virus-specific antibodies 3 months after infection.

INTERPRETATION

The continuous high titre of neutralising antibodies and increased T cell response might support the concept of long-term protective immunity in survivors. The existence of antibody and T cell responses in contacts of individuals with Ebola virus disease adds further evidence to the existence of sub-clinical Ebola virus infection.

FUNDING

US Food & Drug Administration, Horizon 2020 EU EVIDENT, Wellcome, UK Department for International Development.

TRANSLATION

For the French translation of the abstract see Supplementary Materials section.

[Ebola virus (Filoviridae: Ebolavirus: Zaire ebolavirus): fatal adaptation mutations]

Ebola virus disease (EVD) (former Ebola hemorrhagic fever) is one of the most dangerous infectious diseases affecting humans and primates. Since the identification of the first outbreak in 1976, there have been more than 25 outbreaks worldwide, the largest of which escalated into an epidemic in 2014-2016 and caused the death of more than 11,000 people. There are currently 2 independent outbreaks of this disease in the eastern and western parts of the Democratic Republic of the Congo (DRC) at the same time. Bats (Microchiroptera) are supposed to be the natural reservoir of EVD, but the infectious agent has not yet been isolated from them. Most animal viruses are unable to replicate in humans. They have to develop adaptive mutations (AM) to become infectious for humans. In this review based on the results of a number of studies, we hypothesize that the formation of AM occurs directly in the human and primate population and subsequently leads to the development of EVD outbreaks.

A retrospective cohort investigation of seroprevalence of Marburg virus and ebolaviruses in two different ecological zones in Uganda

BACKGROUND

Uganda has experienced seven Ebola Virus Disease (EVD) outbreaks and four Marburg Virus Disease (MVD) outbreaks between 2000 and 2019. We investigated the seroprevalence and risk factors for Marburg virus and ebolaviruses in gold mining communities around Kitaka gold mine in Western Uganda and compared them to non-mining communities in Central Uganda.

METHODS

A questionnaire was administered and human blood samples were collected from three exposure groups in Western Uganda (gold miners, household members of miners, non-miners living within 50 km of Kitaka mine). The unexposed controls group sampled was community members in Central Uganda far away from any gold mining activity which we considered as low-risk for filovirus infection. ELISA serology was used to analyse samples, detecting IgG antibodies against Marburg virus and ebolaviruses (filoviruses). Data were analysed in STATA software using risk ratios and odds ratios.

RESULTS

Miners in western Uganda were 5.4 times more likely to be filovirus seropositive compared to the control group in central Uganda (RR = 5.4; 95% CI 1.5-19.7) whereas people living in high-risk areas in Ibanda and Kamwenge districts were 3.6 more likely to be seropositive compared to control group in Luweeero district (RR = 3.6; 95% CI 1.1-12.2). Among all participants, filovirus seropositivity was 2.6% (19/724) of which 2.3% (17/724) were reactive to Sudan virus only and 0.1% (1/724) to Marburg virus. One individual seropositive for Sudan virus also had IgG antibodies reactive to Bundibugyo virus. The risk factors for filovirus seropositivity identified included mining (AOR = 3.4; 95% CI 1.3-8.5), male sex (AOR = 3.1; 95% CI 1.01-9.5), going inside mines (AOR = 3.1; 95% CI 1.2-8.2), cleaning corpses (AOR = 3.1; 95% CI 1.04-9.1) and contact with suspect filovirus cases (AOR = 3.9, 95% CI 1.04-14.5).

CONCLUSIONS

These findings indicate that filovirus outbreaks may go undetected in Uganda and people involved in artisan gold mining are more likely to be exposed to infection with either Marburg virus or ebolaviruses, likely due to increased risk of exposure to bats. This calls for active surveillance in known high-risk areas for early detection and response to prevent filovirus epidemics.

Serological Detection of Ebola Virus Exposures in Native Non-human Primates of Southern Nigeria

Ebola viruses (family: Filoviridae) are the cause of Ebola virus disease (EVD), a highly fatal illness characterised by haemorrhagic fever syndrome in both humans and non-human primates (NHPs). West Africa was the epicentre of the 2013-2015 EVD epidemic which caused the death of over 11,000 people, including eight casualties in southern Nigeria. Antibodies to filoviruses have been detected among NHPs in some countries, but there is no documented evidence of exposures to filoviruses among NHPs in Nigeria. From August 2015 to February 2017, a total of 142 serum samples were obtained from individual captive and wild animals, belonging to 11 NHP species, in southern Nigeria, and screened for species-specific antibodies to filoviruses belonging to the species; Zaire ebolavirus [Ebola virus (EBOV)], Sudan ebolavirus [Sudan virus (SUDV)], and Marburg marburgvirus [Ravn virus (RAVV)]-using a modified filovirus species-specific ELISA technique. Of the sera tested, 2.1% (3/142) were positive for antibodies to EBOV. The entire 142 sera were negative for SUDV or RAVV. These findings point to the existence of natural exposures of NHPs in southern Nigeria to EBOV. There is need to discourage, the uncontrolled hunting of NHPs in Nigeria for public health safety.

Suspected Exposure to Filoviruses Among People Contacting Wildlife in Southwestern Uganda

Background

Human and filovirus host interactions remain poorly understood in areas where Ebola hemorrhagic fever outbreaks are likely to occur. In the Bwindi region of Uganda, a hot spot of mammalian biodiversity in Africa, human livelihoods are intimately connected with wildlife, creating potential for exposure to filoviruses.

Methods

We tested samples from 331 febrile patients presenting to healthcare facilities near Bwindi Impenetrable Forest, Uganda, by polymerase chain reaction (PCR) analysis and Western blot, using recombinant glycoprotein antigens for Ebola virus (EBOV), Sudan virus (SUDV), Bundibugyo virus (BDBV), and Marburg virus. Behavioral data on contact with wildlife were collected to examine risk factors for filovirus seropositivity.

Results

All patients were negative for active filovirus infection, by PCR analysis. However, patients were seroreactive to SUDV (4.7%), EBOV (5.3%), and BDBV (8.9%), indicating previous exposure. Touching duikers was the most significant risk factor associated with EBOV seropositivity, while hunting primates and touching and/or eating cane rats were significant risk factors for SUDV seropositivity.

Conclusions

People in southwestern Uganda have suspected previous exposure to filoviruses, particularly those with a history of wildlife contact. Circulation of filoviruses in wild animals and subsequent spillover into humans could be more common than previously reported.

Risk assessment of Ebola Reston virus in humans in the Philippines

Objective

There have been five documented outbreaks of Ebola Reston virus (RESTV) in animals epidemiologically linked to the Philippines. This assessment was conducted to determine the risk of RESTV occurring in humans in the Philippines and its potential pathogenicity in humans.

Methods

The World Health Organization Rapid Risk Assessment of Acute Public Health Events Manual was used for the assessment. A literature review was done and a risk assessment matrix was used for the risk characterization of the outbreaks in the Philippines. The risk assessment was conducted by the Philippines Field Epidemiology Training Program.

Results

The risk of RESTV occurring in humans in the Philippines and its potential pathogenicity in humans were both assessed as moderate. Animals involved in RESTV outbreaks in the Philippines were non-human primates and domestic pigs. The presence of RESTV in pigs poses a possibility of genetic evolution of the virus. Although RESTV has been identified in humans, there was no death or illness attributed to the infection. The Philippines Inter-agency Committee on Zoonoses oversees collaboration between the animal and human health sectors for the prevention and control of zoonoses. However, there is no surveillance of risk animals or previously affected farms to monitor and facilitate early identification of cases.

Discussion

The moderate risk of RESTV recurring among humans in the Philippines and its potential pathogenicity in humans reinforces the need for early detection, surveillance and continued studies of RESTV pathogenesis and its health consequences. The One Health approach, with the involvement and coordination of public health, veterinary services and the community, is essential in the detection, control and management of zoonosis.

Serologic Evidence of Ebolavirus Infection in a Population With No History of Outbreaks in the Democratic Republic of the Congo

Background

Previous studies suggest that cases of Ebola virus disease (EVD) may go unreported because they are asymptomatic or unrecognized, but evidence is limited by study designs and sample size.

Methods

A large population-based survey was conducted (n = 3415) to assess animal exposures and behaviors associated with Ebolavirus antibody prevalence in rural Kasai Oriental province of the Democratic Republic of Congo (DRC). Fourteen villages were randomly selected and all healthy individuals ≥1 year of age were eligible.

Results

Overall, 11% of subjects tested positive for Zaire Ebolavirus (EBOV) immunoglobulin G antibodies. Odds of seropositivity were higher for study participants older than 15 years of age and for males. Those residing in Kole (closer to the outbreak site) tested positive at a rate 1.6× higher than Lomela, with seropositivity peaking at a site located between Kole and Lomela. Multivariate analyses of behaviors and animal exposures showed that visits to the forest or hunting and exposure to rodents or duikers predicted a higher likelihood of EBOV seropositivity.

Conclusions

These results provide serologic evidence of Ebolavirus exposure in a population residing in non-EBOV outbreak locations in the DRC and define statistically significant activities and animal exposures that associate with EBOV seropositivity.

Asymptomatic infection and unrecognised Ebola virus disease in Ebola-affected households in Sierra Leone: a cross-sectional study using a new non-invasive assay for antibodies to Ebola virus

BACKGROUND

The frequency of asymptomatic infection with Ebola virus is unclear: previous estimates vary and there is no standard test. Asymptomatic infection with Ebola virus could contribute to population immunity, reducing spread. If people with asymptomatic infection are infectious it could explain re-emergences of Ebola virus disease (EVD) without known contact.

METHODS

We validated a new oral fluid anti-glycoprotein IgG capture assay among survivors from Kerry Town Ebola Treatment Centre and controls from communities unaffected by EVD in Sierra Leone. We then assessed the seroprevalence of antibodies to Ebola virus in a cross-sectional study of household contacts of the survivors. All household members were interviewed. Two reactive tests were required for a positive result, with a third test to resolve any discrepancies.

FINDINGS

The assay had a specificity of 100% (95% CI 98·9-100; 339 of 339 controls tested negative) and sensitivity of 95·9% (89·8-98·9; 93 of 97 PCR-confirmed survivors tested positive). Of household contacts not diagnosed with EVD, 47·6% (229 of 481) had high level exposure (direct contact with a corpse, body fluids, or a case with diarrhoea, vomiting, or bleeding). Among the contacts, 12·0% (95% CI 6·1-20·4; 11 of 92) with symptoms at the time other household members had EVD, and 2·6% (1·2-4·7; 10 of 388) with no symptoms tested positive. Among asymptomatic contacts, seropositivity was weakly correlated with exposure level.

INTERPRETATION

This new highly specific and sensitive assay showed asymptomatic infection with Ebola virus was uncommon despite high exposure. The low prevalence suggests asymptomatic infection contributes little to herd immunity in Ebola, and even if infectious, would account for few transmissions.

FUNDING

Wellcome Trust ERAES Programme, Save the Children.

A systematic review and meta-analysis of seroprevalence surveys of ebolavirus infection

Asymptomatic ebolavirus infection could greatly influence transmission dynamics, but there is little consensus on how frequently it occurs or even if it exists. This paper summarises the available evidence on seroprevalence of Ebola, Sudan and Bundibugyo virus IgG in people without known ebolavirus disease. Through systematic review, we identified 51 studies with seroprevalence results in sera collected from 1961 to 2016. We tabulated findings by study population, contact, assay, antigen and positivity threshold used, and present seroprevalence point estimates and 95% confidence intervals. We classified sampled populations in three groups: those with household or known case-contact; those living in outbreak or epidemic areas but without reported case-contact; and those living in areas with no recorded cases of ebolavirus disease. We performed meta-analysis only in the known case-contact group since this is the only group with comparable exposures between studies. Eight contact studies fitted our inclusion criteria, giving an overall estimate of seroprevalence in contacts with no reported symptoms of 3.3% (95% CI 2.4–4.4, P<0.001), but with substantial heterogeneity.

Forty Years of Ebolavirus Molecular Biology: Understanding a Novel Disease Agent Through the Development and Application of New Technologies

Molecular biology is a broad discipline that seeks to understand biological phenomena at a molecular level, and achieves this through the study of DNA, RNA, proteins, and/or other macromolecules (e.g., those involved in the modification of these substrates). Consequently, it relies on the availability of a wide variety of methods that deal with the collection, preservation, inactivation, separation, manipulation, imaging, and analysis of these molecules. As such the state of the art in the field of ebolavirus molecular biology research (and that of all other viruses) is largely intertwined with, if not driven by, advancements in the technical methodologies available for these kinds of studies. Here we review of the current state of our knowledge regarding ebolavirus biology and emphasize the associated methods that made these discoveries possible.

How severe and prevalent are Ebola and Marburg viruses? A systematic review and meta-analysis of the case fatality rates and seroprevalence

BACKGROUND

Ebola and Marburg virus diseases are said to occur at a low prevalence, but are very severe diseases with high lethalities. The fatality rates reported in different outbreaks ranged from 24-100%. In addition, sero-surveys conducted have shown different seropositivity for both Ebola and Marburg viruses. We aimed to use a meta-analysis approach to estimate the case fatality and seroprevalence rates of these filoviruses, providing vital information for epidemic response and preparedness in countries affected by these diseases.

METHODS

Published literature was retrieved through a search of databases. Articles were included if they reported number of deaths, cases, and seropositivity. We further cross-referenced with ministries of health, WHO and CDC databases. The effect size was proportion represented by case fatality rate (CFR) and seroprevalence. Analysis was done using the metaprop command in STATA.

RESULTS

The weighted average CFR of Ebola virus disease was estimated to be 65.0% [95% CI (54.0-76.0%), I2 = 97.98%] whereas that of Marburg virus disease was 53.8% (26.5-80.0%, I2 = 88.6%). The overall seroprevalence of Ebola virus was 8.0% (5.0%-11.0%, I2 = 98.7%), whereas that for Marburg virus was 1.2% (0.5-2.0%, I2 = 94.8%). The most severe species of ebolavirus was Zaire ebolavirus while Bundibugyo Ebolavirus was the least severe.

CONCLUSIONS

The pooled CFR and seroprevalence for Ebola and Marburg viruses were found to be lower than usually reported, with species differences despite high heterogeneity between studies. Countries with an improved health surveillance and epidemic response have lower CFR, thereby indicating need for improving early detection and epidemic response in filovirus outbreaks.

The serology of Ebolavirus - a wider geographical range, a wider genus of viruses or a wider range of virulence?

Viruses of the genus Ebolavirus are the causative agents of Ebola virus disease (EVD), of which there have been only 25 recorded outbreaks since the discovery of Zaire and Sudan ebolaviruses in the late 1970s. Until the west African outbreak commencing in late 2013, EVD was confined to an area of central Africa stretching from the coast of Gabon through the Congo river basin and eastward to the Great Lakes. Nevertheless, population serological studies since 1976, most of which were carried out in the first two decades after that date, have suggested a wider distribution and more frequent occurrence across tropical Africa. We review this body of work, discussing the various methods employed over the years and the degree to which they can currently be regarded as reliable. We conclude that there is adequate evidence for a wider geographical range of exposure to Ebolavirus or related filoviruses and discuss three possibilities that could account for this: (a) EVD outbreaks have been misidentified as other diseases in the past; (b) unidentified, and clinically milder, species of the genus Ebolavirus circulate over a wider range than the most pathogenic species; and (c) EVD may be subclinical with a frequency high enough that smaller outbreaks may be unidentified. We conclude that the second option is the most likely and therefore predict the future discovery of other, less virulent, members of the genus Ebolavirus.

Multiple circulating infections can mimic the early stages of viral hemorrhagic fevers and possible human exposure to filoviruses in Sierra Leone prior to the 2014 outbreak

Lassa fever (LF) is a severe viral hemorrhagic fever caused by Lassa virus (LASV). The LF program at the Kenema Government Hospital (KGH) in Eastern Sierra Leone currently provides diagnostic services and clinical care for more than 500 suspected LF cases per year. Nearly two-thirds of suspected LF patients presenting to the LF Ward test negative for either LASV antigen or anti-LASV immunoglobulin M (IgM), and therefore are considered to have a non-Lassa febrile illness (NLFI). The NLFI patients in this study were generally severely ill, which accounts for their high case fatality rate of 36%. The current studies were aimed at determining possible causes of severe febrile illnesses in non-LF cases presenting to the KGH, including possible involvement of filoviruses. A seroprevalence survey employing commercial enzyme-linked immunosorbent assay tests revealed significant IgM and IgG reactivity against dengue virus, chikungunya virus, West Nile virus (WNV), Leptospira, and typhus. A polymerase chain reaction-based survey using sera from subjects with acute LF, evidence of prior LASV exposure, or NLFI revealed widespread infection with Plasmodium falciparum malaria in febrile patients. WNV RNA was detected in a subset of patients, and a 419 nt amplicon specific to filoviral L segment RNA was detected at low levels in a single patient. However, 22% of the patients presenting at the KGH between 2011 and 2014 who were included in this survey registered anti-Ebola virus (EBOV) IgG or IgM, suggesting prior exposure to this agent. The 2014 Ebola virus disease (EVD) outbreak is already the deadliest and most widely dispersed outbreak of its kind on record. Serological evidence reported here for possible human exposure to filoviruses in Sierra Leone prior to the current EVD outbreak supports genetic analysis that EBOV may have been present in West Africa for some time prior to the 2014 outbreak.

Development of Prototype Filovirus Recombinant Antigen Immunoassays

BACKGROUND

Throughout the 2014-2015 Ebola outbreak in West Africa, major gaps were exposed in the availability of validated rapid diagnostic platforms, protective vaccines, and effective therapeutic agents. These gaps potentiated the development of prototype rapid lateral flow immunodiagnostic (LFI) assays that are true point-of-contact platforms, for the detection of active Ebola infections in small blood samples.

METHODS

Recombinant Ebola and Marburg virus matrix VP40 and glycoprotein (GP) antigens were used to derive a panel of monoclonal and polyclonal antibodies. Antibodies were tested using a multivariate approach to identify antibody-antigen combinations suitable for enzyme-linked immunosorbent assay (ELISA) and LFI assay development.

RESULTS

Polyclonal antibodies generated in goats were superior reagents for capture and detection of recombinant VP40 in test sample matrices. These antibodies were optimized for use in antigen-capture ELISA and LFI assay platforms. Prototype immunoglobulin M (IgM)/immunoglobulin G (IgG) ELISAs were similarly developed that specifically detect Ebola virus-specific antibodies in the serum of experimentally infected nonhuman primates and in blood samples obtained from patients with Ebola from Sierra Leone.

CONCLUSIONS

The prototype recombinant Ebola LFI assays developed in these studies have sensitivities that are useful for clinical diagnosis of acute ebolavirus infections. The antigen-capture and IgM/IgG ELISAs provide additional confirmatory assay platforms for detecting VP40 and other ebolavirus-specific immunoglobulins.

What is Ebola?

On 23 March 2014, the World Health Organization first announced a new Ebola virus outbreak that started in December 2013 in the eastern part of the Republic of Guinea. Human infections shortly emerged in Liberia, Sierra Leone, and Nigeria. On 30 September 2014, the Centers for Disease Control and Prevention confirmed through laboratory testing the first Ebola virus infection diagnosed in the USA, in a patient who travelled from West Africa to Texas. On 6 October 2014, the first human infection occurring outside of Africa was reported, in a Spanish nurse who treated two priests, both of whom died, and on 23 October 2014, the first human infection was reported in New York City. To date, the 2014 Ebola virus outbreak is the longest, largest, and most persistent one since 1976, when the virus was first identified in humans, and the number of human cases exceeded, as of mid-September 2014, the cumulative number of infections from all the previous outbreaks. The early clinical presentation overlaps with other infectious diseases, opening differential diagnosis difficulties. Understanding the transmission routes and identifying the natural reservoir of the virus are additional challenges in studying Ebola hemorrhagic fever outbreaks. Ebola virus is as much a public health challenge for developing countries as it is for the developed world, and previous outbreaks underscored that the relative contribution of the risk factors may differ among outbreaks. The implementation of effective preparedness plans is contingent on integrating teachings from previous Ebola virus outbreaks with those from the current outbreak and with lessons provided by other infectious diseases, along with developing a multifaceted inter-disciplinary and cross-disciplinary framework that should be established and shaped by biomedical as well as sociopolitical sciences.

A new approach for monitoring ebolavirus in wild great apes

BACKGROUND

Central Africa is a "hotspot" for emerging infectious diseases (EIDs) of global and local importance, and a current outbreak of ebolavirus is affecting multiple countries simultaneously. Ebolavirus is suspected to have caused recent declines in resident great apes. While ebolavirus vaccines have been proposed as an intervention to protect apes, their effectiveness would be improved if we could diagnostically confirm Ebola virus disease (EVD) as the cause of die-offs, establish ebolavirus geographical distribution, identify immunologically naïve populations, and determine whether apes survive virus exposure.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report the first successful noninvasive detection of antibodies against Ebola virus (EBOV) from wild ape feces. Using this method, we have been able to identify gorillas with antibodies to EBOV with an overall prevalence rate reaching 10% on average, demonstrating that EBOV exposure or infection is not uniformly lethal in this species. Furthermore, evidence of antibodies was identified in gorillas thought previously to be unexposed to EBOV (protected from exposure by rivers as topological barriers of transmission).

CONCLUSIONS/SIGNIFICANCE

Our new approach will contribute to a strategy to protect apes from future EBOV infections by early detection of increased incidence of exposure, by identifying immunologically naïve at-risk populations as potential targets for vaccination, and by providing a means to track vaccine efficacy if such intervention is deemed appropriate. Finally, since human EVD is linked to contact with infected wildlife carcasses, efforts aimed at identifying great ape outbreaks could have a profound impact on public health in local communities, where EBOV causes case-fatality rates of up to 88%.

Clinical manifestations and case management of Ebola haemorrhagic fever caused by a newly identified virus strain, Bundibugyo, Uganda, 2007-2008

A confirmed Ebola haemorrhagic fever (EHF) outbreak in Bundibugyo, Uganda, November 2007–February 2008, was caused by a putative new species (Bundibugyo ebolavirus). It included 93 putative cases, 56 laboratory-confirmed cases, and 37 deaths (CFR = 25%). Study objectives are to describe clinical manifestations and case management for 26 hospitalised laboratory-confirmed EHF patients. Clinical findings are congruous with previously reported EHF infections. The most frequently experienced symptoms were non-bloody diarrhoea (81%), severe headache (81%), and asthenia (77%). Seven patients reported or were observed with haemorrhagic symptoms, six of whom died. Ebola care remains difficult due to the resource-poor setting of outbreaks and the infection-control procedures required. However, quality data collection is essential to evaluate case definitions and therapeutic interventions, and needs improvement in future epidemics. Organizations usually involved in EHF case management have a particular responsibility in this respect.

[Filoviruses]

Filoviruses (Ebola and Marburg viruses) cause severe hemorrhagic fever in humans and nonhuman primates. No effective prophylaxis or treatment for filovirus diseases is yet commercially available. Recent studies have advanced our knowledge of filovirus protein functions and interaction between viral and host factors in the replication cycle. Current findings on the ecology of filoviruses (i.e., natural infection of nonprimate animals and discovery of a new member of filoviruses in Europe) have also provided new insights into the epidemiology of Ebola and Marburg hemorrhagic fever. This article reviews the fundamental aspects of filovirus biology and the latest topics on filovirus research.

Development of an immunofiltration-based antigen-detection assay for rapid diagnosis of Ebola virus infection

Ebola virus (EBOV) has caused outbreaks of severe viral hemorrhagic fever in regions of Central Africa where medical facilities are ill equipped and diagnostic capabilities are limited. To obtain a reliable test that can be implemented easily under these conditions, monoclonal antibodies to the EBOV matrix protein (VP40), which previously had been found to work in a conventional enzyme-linked immunosorbent assay, were used to develop an immunofiltration assay for the detection of EBOV antigen in chemically inactivated clinical specimens. The assay was evaluated by use of defined virus stocks and specimens from experimentally infected animals. Its field application was tested during an outbreak of Ebola hemorrhagic fever in 2003. Although the original goal was to develop an assay that would detect all EBOV species, only the Zaire and Sudan species were detected in practice. The assay represents a first-generation rapid field test for the detection of EBOV antigen that can be performed in 30 min without electrical power or expensive or sensitive equipment.

Ebola virus VP24 proteins inhibit the interaction of NPI-1 subfamily karyopherin alpha proteins with activated STAT1

The Zaire ebolavirus protein VP24 was previously demonstrated to inhibit alpha/beta interferon (IFN-alpha/beta)- and IFN-gamma-induced nuclear accumulation of tyrosine-phosphorylated STAT1 (PY-STAT1) and to inhibit IFN-alpha/beta- and IFN-gamma-induced gene expression. These properties correlated with the ability of VP24 to interact with the nuclear localization signal receptor for PY-STAT1, karyopherin alpha1. Here, VP24 is demonstrated to interact not only with overexpressed but also with endogenous karyopherin alpha1. Mutational analysis demonstrated that VP24 binds within the PY-STAT1 binding region located in the C terminus of karyopherin alpha1. In addition, VP24 was found to inhibit PY-STAT1 binding to both overexpressed and endogenous karyopherin alpha1. We assessed the binding of both PY-STAT1 and the VP24 proteins from Zaire, mouse-adapted Zaire, and Reston Ebola viruses for interaction with all six members of the human karyopherin alpha family. We found, in contrast to previous studies, that PY-STAT1 can interact not only with karyopherin alpha1 but also with karyopherins alpha5 and alpha6, which together comprise the NPI-1 subfamily of karyopherin alphaS. Similarly, all three VP24s bound and inhibited PY-STAT1 interaction with karyopherins alpha1, alpha5, and alpha6. Consistent with their ability to inhibit the karyopherin-PY-STAT1 interaction, Zaire, mouse-adapted Zaire, and Reston Ebola virus VP24s displayed similar capacities to inhibit IFN-beta-induced gene expression in human and mouse cells. These findings suggest that VP24 inhibits interaction of PY-STAT1 with karyopherins alpha1, alpha5, or alpha6 by binding within the PY-STAT1 binding region of the karyopherins and that this function is conserved among the VP24 proteins of different Ebola virus species.

Crystal structure of the C-terminal domain of Ebola virus VP30 reveals a role in transcription and nucleocapsid association

Transcription of the highly pathogenic Ebola virus depends on VP30, a nucleocapsid-associated Ebola virus-specific transcription factor. The transcription activator VP30 was shown to play an essential role in Ebola virus replication, most likely by stabilizing nascent mRNA. Here we present the crystal structure of the C-terminal domain (CTD) of VP30 (VP30(CTD)) at 2.0-A resolution. VP30(CTD) folds independently into a dimeric helical assembly. The VP30(CTD) dimers assemble into hexamers that are present in virions, by an oligomerization domain located in the N terminus of VP30. Mutagenesis of conserved charged amino acids on VP30(CTD) revealed that two regions, namely a basic cluster around Lys-180 and Glu-197, are required for nucleocapsid interaction. However, only mutagenesis of the basic cluster was shown to impair transcription activation, suggesting that both processes are regulated independently. The structure and the mutagenesis results reveal a potential pocket for small-molecule inhibitors that might prevent VP30 activity and thus virus propagation as it has been shown previously by peptides, which interfere with VP30 homooligomerization.

Morbidity and mortality of wild animals in relation to outbreaks of Ebola haemorrhagic fever in Gabon, 1994–2003

Antibody to Ebola virus was found in 14 (1.2%) of 1147 human sera collected in Gabon in 1981-1997. Six seropositive subjects were bled in the northeast in 1991, more than 3 years prior to recognition of the first known outbreak of Ebola haemorrhagic fever (EHF), whilst eight came from the southwest where the disease has not been recognised. It has been reported elsewhere that 98 carcasses of wild animals were found in systematic studies in northeastern Gabon and adjoining northwestern Republic of the Congo (RoC) during five EHF epidemics in August 2001 to June 2003, with Ebola virus infection being confirmed in 14 carcasses. During the present opportunistic observations, reports were investigated of a further 397 carcasses, mainly gorillas, chimpanzees, mandrills and bush pigs, found by rural residents in 35 incidents in Gabon and RoC during 1994-2003. Sixteen incidents had temporal and/or spatial coincidence with confirmed EHF outbreaks, and the remaining 19 appeared to represent extension of disease from such sites. There appeared to be sustained Ebola virus activity in the northeast in 1994-1999, with sequential spread from 1996 onwards, first westwards, then southerly, and then northeastwards, reaching the Gabon-RoC border in 2001. This implies that there was transmission of infection between wild mammals, but the species involved are highly susceptible and unlikely to be natural hosts of the virus.

Wild animal mortality monitoring and human Ebola outbreaks, Gabon and Republic of Congo, 2001-2003

All human Ebola virus outbreaks during 2001-2003 in the forest zone between Gabon and Republic of Congo resulted from handling infected wild animal carcasses. After the first outbreak, we created an Animal Mortality Monitoring Network in collaboration with the Gabonese and Congolese Ministries of Forestry and Environment and wildlife organizations (Wildlife Conservation Society and Programme de Conservation et Utilisation Rationnelle des Ecosystemes Forestiers en Afrique Centrale) to predict and possibly prevent human Ebola outbreaks. Since August 2001, 98 wild animal carcasses have been recovered by the network, including 65 great apes. Analysis of 21 carcasses found that 10 gorillas, 3 chimpanzees, and 1 duiker tested positive for Ebola virus. Wild animal outbreaks began before each of the 5 human Ebola outbreaks. Twice we alerted the health authorities to an imminent risk for human outbreaks, weeks before they occurred.

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.

An efficient method to make human monoclonal antibodies from memory B cells: potent neutralization of SARS coronavirus

Passive serotherapy can confer immediate protection against microbial infection, but methods to rapidly generate human neutralizing monoclonal antibodies are not yet available. We have developed an improved method for Epstein-Barr virus transformation of human B cells. We used this method to analyze the memory repertoire of a patient who recovered from severe acute respiratory syndrome coronavirus (SARS-CoV) infection and to isolate monoclonal antibodies specific for different viral proteins, including 35 antibodies with in vitro neutralizing activity ranging from 10⁻⁸M to 10⁻¹¹M. One such antibody confers protection in vivo in a mouse model of SARS-CoV infection. These results show that it is possible to interrogate the memory repertoire of immune donors to rapidly and efficiently isolate neutralizing antibodies that have been selected in the course of natural infection.

Production of monoclonal antibodies and development of an antigen capture ELISA directed against the envelope glycoprotein GP of Ebola virus

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.

Oligomerization of Ebola virus VP30 is essential for viral transcription and can be inhibited by a synthetic peptide

Transcription of Ebola virus (EBOV)-specific mRNA is driven by the nucleocapsid proteins NP, VP35, and L. This process is further dependent on VP30, an essential EBOV-specific transcription factor. The present study addresses the self-assembly of VP30 and the functional significance of this process for viral transcription and propagation. Essential for oligomerization of VP30 is a region spanning amino acids 94-112. Within this region a cluster of four leucine residues is of critical importance. Mutation of only one of these leucine residues resulted in oligomerization-deficient VP30 molecules that were no longer able to support EBOV-specific transcription. The essential role of homo-oligomerization for the function of VP30 was further corroborated by the finding that mixed VP30 oligomers consisting of VP30 and transcriptionally inactive VP30 mutants were impaired in their ability to support EBOV transcription. The dominant negative effect of these VP30 mutants was dependent on their ability to bind to VP30. The oligomerization of VP30 could be dose dependently inhibited by a 25-mer peptide (E30pep-wt) derived from the presumed oligomerization domain (IC50,1 mum). A control peptide (E30pep-3LA), in which three leucines were changed to alanine, had no inhibitory effect. Thus, E30pep-wt seemed to bind efficiently to VP30 and consequently blocked the oligomerization of the protein. When E30pep-wt was transfected into EBOV-infected cells, the peptide inhibited viral replication suggesting that inhibition of VP30 oligomerization represents a target for EBOV antiviral drugs.

Development, characterization and use of monoclonal VP40-antibodies for the detection of Ebola virus

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.

Mapping of two dominant sites of VP35 of Marburg virus

Five types of anti-VP35 monoclonal antibodies (MAbs), four immune sera against Marburg virus (MBGV), and 11 overlapping recombinant VP35 fragments were used to map the epitopes for VP35 of MBGV. The purified full-size recombinant VP35 was highly immunogenic and retained the B-cell epitopes that were identical to those of the viral VP35. Two major sites on VP35 and a set of truncated VP35 fragments were found by use of an enzyme immunoassay and immunoblot. Site I was located in a region between amino acids 1 and 174 of the VP35 sequence, and only polyclonal antibodies (PAbs) against MBGV recognized epitopes at this site. Site II was mapped by use of anti-VP35 MAbs to the region between amino acid residues 167 and 278 of VP35. Amino acids 252-278 of VP35 might be involved in the formation of the epitopes for MAbs. B-cell epitopes were not found on the C-terminus of VP35 by use of PAbs or MAbs.

The matrix protein VP40 from Ebola virus octamerizes into pore-like structures with specific RNA binding properties

The Ebola virus membrane-associated matrix protein VP40 is thought to be crucial for assembly and budding of virus particles. Here we present the crystal structure of a disk-shaped octameric form of VP40 formed by four antiparallel homodimers of the N-terminal domain. The octamer binds an RNA triribonucleotide containing the sequence 5'-U-G-A-3' through its inner pore surface, and its oligomerization and RNA binding properties are facilitated by two conformational changes when compared to monomeric VP40. The selective RNA interaction stabilizes the ring structure and confers in vitro SDS resistance to octameric VP40. SDS-resistant octameric VP40 is also found in Ebola virus-infected cells, which suggests that VP40 has an additional function in the life cycle of the virus besides promoting virus assembly and budding off the plasma membrane.

Phosphorylation of VP30 impairs ebola virus transcription

Transcription of the highly pathogenic Ebola virus (EBOV) is dependent on VP30, a constituent of the viral nucleocapsid complex. Here we present evidence that phosphorylation of VP30, which takes place at six N-terminal serine residues and one threonine residue, is of functional significance. Replacement of the phosphoserines by alanines resulted in an only slightly phosphorylated VP30 (VP30(6A)) that is still able to activate EBOV-specific transcription in a plasmid-based minigenome system. VP30(6A), however, did not bind to inclusions that are induced by the major nucleocapsid protein NP. Three intracellular phosphatases (PP1, PP2A, and PP2C) have been determined to dephosphorylate VP30. The presence of okadaic acid (OA), an inhibitor of PP1 and PP2A, had the same negative effect on transcription activation by VP30 as the substitution of the six phosphoserines for aspartate residues. OA, however, did not impair transcription when VP30 was replaced by VP30(6A). In EBOV-infected cells, OA blocked virus growth dose-dependently. The block was mediated by the extensive phosphorylation of VP30, which is evidenced by the result that expression of VP30(6A), in trans, led to the progression of EBOV infection in the presence of OA. In conclusion, phosphorylation of VP30 was shown to regulate negatively transcription activation and positively binding to the NP inclusions.

Interactions of Marburg virus nucleocapsid proteins

In this study, the components of Marburg virus nucleocapsid complex were determined, and interactions between the compounds were investigated. Using salt dissociation of isolated virions, four proteins (NP, VP35, VP30, and L) remained attached to the core complex. Same proteins were detected intracellularly to be localized in MBGV-induced inclusion bodies, which are presumed to represent areas of nucleocapsid formation. To investigate interactions between the four proteins, immunofluorescence analysis of coexpressed proteins was carried out. Complexes between NP-VP35 and NP-VP30 were formed, which was demonstrated by redistribution of VP35 and VP30 into NP-induced inclusion bodies. Furthermore, complexes between L and VP35 were detected by coimmunoprecipitation. Using deletion mutants of L, the binding site of VP35 on L could be restricted to the N-terminal 530 amino-acid residues. Coexpression of NP, VP35, and L led to the formation of a triple complex where VP35 linked NP and L. The detected complexes are presumed to represent the key components of the MBGV transcription and replication machinery.

Inactivated Marburg virus elicits a nonprotective immune response in Rhesus monkeys

In the present work the kinetics of some indices of immunity (tumor necrosis factor (TNF), interferon (IFN), natural killer cells (NK), lymphocyte proliferation activity, virus-specific antibodies, CD4/CD8 ratio) in response to Marburg virus infection in Macaca mulatta were studied. The different kinetics of immunological parameters for animals which survived Marburg virus infection and for animals which died after infection are shown. A comparison of the indices of IFN, TNF and spontaneous lymphocyte proliferation activity in Macaca mulatta infected with Marburg virus at different stages of life shows the relationship between the increase of these indices and the decrease in the animals' lifespan. Marburg virus immunosuppressive properties were corroborated by studying lymphocyte proliferation activity in response to antigenic stimulation in vitro and the CD4/CD8 index during experimental Marburg virus infection in Macaca mulatta. We conclude that the disease outcome depends on the dynamics of certain immunologic indices such as TNF and IFN.

Emerging and reemerging of filoviruses

Filoviruses are causative agents of a hemorrhagic fever in man with mortalities ranging from 22 to 88%. They are enveloped, nonsegmented negative-stranded RNA viruses and are separated into two types, Marburg and Ebola, which can be serologically, biochemically and genetically distinguished. In general, there is little genetic variability among viruses belonging to the Marburg type. The Ebola type, however, is subdivided into at least three distinct subtypes. Marburg virus was first isolated during an outbreak in Europe in 1967. Ebola virus emerged in 1976 as the causative agent of two simultaneous outbreaks in southern Sudan and northern Zaire. The reemergence of Ebola, subtype Zaire, in Kikwit 1995 caused a worldwide sensation, since it struck after a sensibilization on the danger of Ebola virus disease. Person-to-person transmission by intimate contact is the main route of infection, but transmission by droplets and small aerosols among infected individuals is discussed. The natural reservoir for filoviruses remains a mystery. Filoviruses are prime examples for emerging pathogens. Factors that may be involved in emergence are international commerce and travel, limited experience in diagnosis and case management, import of nonhuman primates, and the potential of filoviruses for rapid evolution.

Replication of Marburg virus in human endothelial cells. A possible mechanism for the development of viral hemorrhagic disease

Marburg and Ebola virus, members of the family Filoviridae, cause a severe hemorrhagic disease in humans and primates. The disease is characterized as a pantropic virus infection often resulting in a fulminating shock associated with hemorrhage, and death. All known histological and pathophysiological parameters of the disease are not sufficient to explain the devastating symptoms. Previous studies suggested a nonspecific destruction of the endothelium as a possible mechanism. Concerning the important regulatory functions of the endothelium (blood pressure, anti-thrombogenicity, homeostasis), we examined Marburg virus replication in primary cultures of human endothelial cells and organ cultures of human umbilical cord veins. We show here that Marburg virus replicates in endothelial cells almost as well as in monkey kidney cells commonly used for virus propagation. Our data support the concept that the destruction of endothelial cells resulting from Marburg virus replication is a possible mechanism responsible for the hemorrhagic disease and the shock syndrome typical of this infection.

Molecular biology and evolution of filoviruses

The family Filoviridae contains extremely pathogenic human viruses causing a fulminating, febrile hemorrhagic disease. Filoviruses are enveloped, filamentous particles with a nonsegmented negative-strand RNA genome showing the gene arrangement 3'-NP-VP35-VP40-GP-VP30-VP24-L-5'. Genes are flanked by highly conserved transcriptional signals and are generally separated by variable intergenic regions. They are transcribed into monocistronic polyadenylated messenger RNAs which contain relatively long 5' and 3' untranslated regions. Seven structural proteins are encoded by the genome of which four form the helical nucleocapsid (NP-VP35-VP30-L), two are membrane-associated (VP40-VP24), and one is a transmembrane glycoprotein (GP). Comparison of filovirus genomes with those of other nonsegmented negative-strand RNA viruses suggest comparable mechanisms of transcription and replication and a common evolutionary lineage for all these viruses. Sequence analyses of single genes, however, showed that filoviruses are more closely related to paramyxoviruses, particularly human respiratory syncytial virus. These data support the concept of the taxonomic order Mononegavirales for all nonsegmented negative-strand RNA viruses and the classification of Marburg virus, Ebola virus, and Reston virus in the family Filoviridae, separate from the families Paramyxoviridae and Rhabdoviridae.