Serologic cross-reactivity of human IgM and IgG antibodies to five species of Ebola virus

Serological evidence of zoonotic filovirus exposure among bushmeat hunters in Guinea

Human Ebola virus (EBOV) outbreaks caused by persistent EBOV infection raises questions on the role of zoonotic spillover in filovirus epidemiology. To characterise filovirus zoonotic exposure, we collected cross-sectional serum samples from bushmeat hunters (n = 498) in Macenta Prefecture Guinea, adjacent to the index site of the 2013 EBOV-Makona spillover event. We identified distinct immune signatures (20/498, 4.0%) to multiple EBOV antigens (GP, NP, VP40) using stepwise ELISA and Western blot analysis and, live EBOV neutralisation (5/20; 25%). Using comparative serological data from PCR-confirmed survivors of the 2013-2016 EBOV outbreak, we demonstrated that most signatures (15/20) were not plausibly explained by prior EBOV-Makona exposure. Subsequent data-driven modelling of EBOV immunological outcomes to remote-sensing environmental data also revealed consistent associations with intact closed canopy forest. Together our findings suggest exposure to other closely related filoviruses prior to the 2013-2016 West Africa epidemic and highlight future surveillance priorities.

Correlation between pseudotyped virus and authentic virus neutralisation assays, a systematic review and meta-analysis of the literature

Background

The virus neutralization assay is a principal method to assess the efficacy of antibodies in blocking viral entry. Due to biosafety handling requirements of viruses classified as hazard group 3 or 4, pseudotyped viruses can be used as a safer alternative. However, it is often queried how well the results derived from pseudotyped viruses correlate with authentic virus. This systematic review and meta-analysis was designed to comprehensively evaluate the correlation between the two assays.

Methods

Using PubMed and Google Scholar, reports that incorporated neutralisation assays with both pseudotyped virus, authentic virus, and the application of a mathematical formula to assess the relationship between the results, were selected for review. Our searches identified 67 reports, of which 22 underwent a three-level meta-analysis.

Results

The three-level meta-analysis revealed a high level of correlation between pseudotyped viruses and authentic viruses when used in an neutralisation assay. Reports that were not included in the meta-analysis also showed a high degree of correlation, with the exception of lentiviral-based pseudotyped Ebola viruses.

Conclusion

Pseudotyped viruses identified in this report can be used as a surrogate for authentic virus, though care must be taken in considering which pseudotype core to use when generating new uncharacterised pseudotyped viruses.

Low seroprevalence of Ebola virus in health care providers in an endemic region (Tshuapa province) of the Democratic Republic of the Congo

INTRODUCTION

A serosurvey among health care providers (HCPs) and frontliners of an area previously affected by Ebola virus disease (EVD) in the Democratic Republic of the Congo (DRC) was conducted to assess the seroreactivity to Ebola virus antigens.

METHODS

Serum samples were collected in a cohort of HCPs and frontliners (n = 698) participants in the EBL2007 vaccine trial (December 2019 to October 2022). Specimens seroreactive for EBOV were confirmed using either the Filovirus Animal Nonclinical Group (FANG) ELISA or a Luminex multiplex assay.

RESULTS

The seroreactivity to at least two EBOV-Mayinga (m) antigens was found in 10 (1.4%: 95% CI, 0.7-2.6) samples for GP-EBOV-m + VP40-EBOV-m, and 2 (0.3%: 95% CI, 0.0-1.0) samples for VP40-EBOV-m + NP-EBOV-m using the Luminex assay. Seroreactivity to GP-EBOV-Kikwit (k) was observed in 59 (8.5%: 95%CI, 6.5-10.9) samples using FANG ELISA.

CONCLUSION

In contrast to previous serosurveys, a low seroprevalence was found in the HCP and frontline population participating in the EBL2007 Ebola vaccine trial in Boende, DRC. This underscores the high need for standardized antibody assays and cutoffs in EBOV serosurveys to avoid the broad range of reported EBOV seroprevalence rates in EBOV endemic areas.

The rVSV-EBOV vaccine provides limited cross-protection against Sudan virus in guinea pigs

Recombinant vesicular stomatitis viruses (rVSVs) engineered to express heterologous viral glycoproteins have proven to be remarkably effective vaccines. Indeed, rVSV-EBOV, which expresses the Ebola virus (EBOV) glycoprotein, recently received clinical approval in the United States and Europe for its ability to prevent EBOV disease. Analogous rVSV vaccines expressing glycoproteins of different human-pathogenic filoviruses have also demonstrated efficacy in pre-clinical evaluations, yet these vaccines have not progressed far beyond research laboratories. In the wake of the most recent outbreak of Sudan virus (SUDV) in Uganda, the need for proven countermeasures was made even more acute. Here we demonstrate that an rVSV-based vaccine expressing the SUDV glycoprotein (rVSV-SUDV) generates a potent humoral immune response that protects guinea pigs from SUDV disease and death. Although the cross-protection generated by rVSV vaccines for different filoviruses is thought to be limited, we wondered whether rVSV-EBOV might also provide protection against SUDV, which is closely related to EBOV. Surprisingly, nearly 60% of guinea pigs that were vaccinated with rVSV-EBOV and challenged with SUDV survived, suggesting that rVSV-EBOV offers limited protection against SUDV, at least in the guinea pig model. These results were confirmed by a back-challenge experiment in which animals that had been vaccinated with rVSV-EBOV and survived EBOV challenge were inoculated with SUDV and survived. Whether these data are applicable to efficacy in humans is unknown, and they should therefore be interpreted cautiously. Nevertheless, this study confirms the potency of the rVSV-SUDV vaccine and highlights the potential for rVSV-EBOV to elicit a cross-protective immune response.

Tissue replication and mucosal swab detection of Sosuga virus in Syrian hamsters in the absence of overt tissue pathology and clinical disease

Human infection with Sosuga virus (SOSV), a recently discovered pathogenic paramyxovirus, has been reported in one individual to date. No animal models of disease are currently available for SOSV. Here, we describe initial characterization of experimental infection in Syrian hamsters, including kinetics of virus dissemination and replication, and the corresponding clinical parameters, immunological responses, and histopathology. We demonstrate susceptibility of hamsters to infection in the absence of clinical signs or significant histopathologic findings in tissues.

Diagnostics of Ebola virus

Ebola is a highly pathogenic virus, which in humans reaches a mortality rate above 50%. Due to a lack of laboratories in territories where Ebola viruses are endemic and the limited number of surveillance programmes, tests for the confirmation of suspected cases of Ebola are often performed in Reference Laboratories. While this provides guarantees regarding the accuracy of results, the shipment of samples to a centralized facility where the diagnostic test can be performed and the time required to achieve the results takes several days, which increases costs and entails delays in the isolation of positive subjects and therapeutic intervention with negative consequences both for patients and the community. Molecular tests have been the most frequently used tool in Ebola diagnosis in recent outbreaks. One of the most commonly used molecular tests is the Real-Star Altona, which targets a conserved area of the L gene. This assay showed different sensitivities depending on the Ebola virus: 471 copies/mL (EBOV) and 2871 copies/ml (SUDAN virus). The Cepheid system also showed good sensitivity (232 copies/mL). The LAMP platform is very promising because, being an isothermal reaction, it does not require high-precision instrumentation and can be considered a Point of Care (PoC) tool. Its analytical sensitivity is 1 copy/reaction. However, since data from real life studies are not yet available, it is premature to give any indications on its feasibility. Moreover, in November 2014, the WHO recommended the development of rapid diagnostic tests (RDT) according to ASSURED criteria. Several RDT assays have since been produced, most of which are rapid tests based on the search for antibody anti-Ebola viral proteins with immunochromatographic methods. Several viral antigens are used for this purpose: VP40, NP and GP. These assays show different sensitivities according to the protein used: VP40 57.4-93.1%, GP 53-88.9% and 85% for NP compared to reference molecular assays. From these results, it can be deduced that no RDT reaches the 99% sensitivity recommended by the WHO and therefore any RDT negative results in suspected cases should be confirmed with a molecular test.

A Retrospective Study of the Seroprevalence of Dengue Virus and Chikungunya Virus Exposures in Nigeria, 2010–2018

Arboviruses are important public health threats in many regions of the world. Nigeria has experienced outbreaks of arboviruses over the past decades, leading to concerns of widespread endemicity, which are frequently misdiagnosed. This study aimed to determine the seroprevalence of dengue virus (DENV) (a flavivirus) and chikungunya virus (CHIKV) (an alphavirus) infections in three major population centers of Nigeria. A convenience sample of 701 sera was collected from both healthy and febrile participants between August 2010 and March 2018. Sera were tested for prior exposure to CHIKV virus and DENV using indirect IgG ELISA. Results showed that 54.1% (379/701) of participants were seropositive for anti-DENV antibodies, 41.3% (290/701) were seropositive for anti-CHIKV antibodies, and 20.1% (141/701) had previous exposure to both. The seropositivity for prior CHIKV exposure and prior exposure to DENV and CHIKV was significantly associated with age (CHIKV: OR = 2.7 (95% CI: 1.7–4.3); DENV and CHIKV: OR = 2.2 (95% CI: 1.2–4.0) for adults compared to participants under 18 years old). Overall, the high seropositivity across all age groups suggests that arboviral infections are prevalent in Nigeria and indicates that surveillance and further epidemiological studies are required to determine the true burden of these infections and the spectrum of diseases associated with these exposures.

Naturally acquired antibody kinetics against Plasmodium vivax antigens in people from a low malaria transmission region in western Thailand

BACKGROUND

Plasmodium vivax (P. vivax) is the dominant Plasmodium spp. causing the disease malaria in low-transmission regions outside of Africa. These regions often feature high proportions of asymptomatic patients with sub-microscopic parasitaemia and relapses. Naturally acquired antibody responses are induced after Plasmodium infection, providing partial protection against high parasitaemia and clinical episodes. However, previous work has failed to address the presence and maintenance of such antibody responses to P. vivax particularly in low-transmission regions.

METHODS

We followed 34 patients in western Thailand after symptomatic P. vivax infections to monitor antibody kinetics over 9 months, during which no recurrent infections occurred. We assessed total IgG, IgG subclass and IgM levels to up to 52 P. vivax proteins every 2-4 weeks using a multiplexed Luminex® assay and identified protein-specific variation in antibody longevity. Mathematical modelling was used to generate the estimated half-life of antibodies, long-, and short-lived antibody-secreting cells.

RESULTS

Generally, an increase in antibody level was observed within 1-week post symptomatic infection, followed by an exponential decay of different rates. We observed mostly IgG1 dominance and IgG3 sub-dominance in this population. IgM responses followed similar kinetic patterns to IgG, with some proteins unexpectedly inducing long-lived IgM responses. We also monitored antibody responses against 27 IgG-immunogenic antigens in 30 asymptomatic individuals from a similar region. Our results demonstrate that most antigens induced robust and long-lived total IgG responses following asymptomatic infections in the absence of (detected) boosting infections.

CONCLUSIONS

Our work provides new insights into the development and maintenance of naturally acquired immunity to P. vivax and will guide the potential use of serology to indicate immune status and/or identify populations at risk.

First laboratory confirmation and sequencing of Zaire ebolavirus in Uganda following two independent introductions of cases from the 10th Ebola Outbreak in the Democratic Republic of the Congo, June 2019

Uganda established a domestic Viral Hemorrhagic Fever (VHF) testing capacity in 2010 in response to the increasing occurrence of filovirus outbreaks. In July 2018, the neighboring Democratic Republic of Congo (DRC) experienced its 10th Ebola Virus Disease (EVD) outbreak and for the duration of the outbreak, the Ugandan Ministry of Health (MOH) initiated a national EVD preparedness stance. Almost one year later, on 10th June 2019, three family members who had contracted EVD in the DRC crossed into Uganda to seek medical treatment.

Samples were collected from all the suspected cases using internationally established biosafety protocols and submitted for VHF diagnostic testing at Uganda Virus Research Institute. All samples were initially tested by RT-PCR for ebolaviruses, marburgviruses, Rift Valley fever (RVF) virus and Crimean-Congo hemorrhagic fever (CCHF) virus. Four people were identified as being positive for Zaire ebolavirus, marking the first report of Zaire ebolavirus in Uganda. In-country Next Generation Sequencing (NGS) and phylogenetic analysis was performed for the first time in Uganda, confirming the outbreak as imported from DRC at two different time point from different clades. This rapid response by the MoH, UVRI and partners led to the control of the outbreak and prevention of secondary virus transmission.

An Environmental Niche Model to Estimate the Potential Presence of Venezuelan Equine Encephalitis Virus in Costa Rica

Venezuelan equine encephalitis virus (VEEV) is an arbovirus transmitted by arthropods, widely distributed in the Americas that, depending on the subtype, can produce outbreaks or yearly cases of encephalitis in horses and humans. The symptoms are similar to those caused by dengue virus and in the worst-case scenario, involve encephalitis, and death. MaxEnt is software that uses climatological, geographical, and occurrence data of a particular species to create a model to estimate possible niches that could have these favorable conditions. We used MaxEnt with a total of 188 registers of VEEV presence, and 20 variables, (19 bioclimatological plus altitude) to determine the niches promising for the presence of VEEV. The area under the ROC curve (AUC) value for the model with all variables was 0.80 for the training data and 0.72 for the test. The variables with the highest contribution to the model were Bio11 (mean temperature of the coldest quarter) 32.5%, Bio17 (precipitation of the driest quarter) 16.9%, Bio2 (annual mean temperature) 15.1%, altitude (m.a.s.l) 6.6%, and Bio18 (precipitation of the warmest quarter) 6.2%. The product of this research will be useful under the one health scheme to animal and human health authorities to forecast areas with high propensity for VEEV cases in the future.

Investigation of Ebolavirus exposure in pigs presented for slaughter in Uganda

In 2008, an outbreak of Reston ebolavirus (RESTV) in pigs in the Philippines expanded our understanding of the host range of ebolaviruses. Subsequent experimental infections with the human‐pathogenic species Zaire ebolavirus (EBOV) confirmed that pigs are susceptible to African species of ebolaviruses. Pig keeping has become an increasingly important livelihood strategy throughout parts of sub‐Saharan Africa, driven by increasing demand for pork. The growth in pig keeping is particularly rapid in Uganda, which has the highest per capita pork consumption in East Africa and a history of sporadic human outbreaks of Ebola virus disease (EVD). Using a systematic sampling protocol, we collected sera from 658 pigs presented for slaughter in Uganda between December 2015 and October 2016. Forty‐six pigs (7%) were seropositive based on ELISA tests at two different institutions. Seropositive pigs had antibodies that bound to Sudan NP (n = 27), Zaire NP (Kikwit; n = 8) or both NPs (n = 11). Sera from 4 of the ELISA‐positive pigs reacted in Western blot (EBOV NP = 1; RESTV NP = 2; both NPs = 2), and one sample had full neutralizing antibody against Sudan ebolavirus (SUDV) in virus neutralization tests. Pigs sampled in June 2016 were significantly more likely to be seropositive than pigs sampled in October 2016 (p = .03). Seropositive pigs were sourced from all regions except Western region. These observed temporal and spatial variations are suggestive of multiple introductions of ebolaviruses into the pig population in Uganda. This is the first report of exposure of pigs in Uganda to ebolaviruses and the first to employ systematic abattoir sampling for ebolavirus surveillance during a non‐outbreak period. Future studies will be necessary to further define the role pigs play (if any) in ebolavirus maintenance and transmission so that potential risks can be mitigated.

Bats as putative Zaire ebolavirus reservoir hosts and their habitat suitability in Africa

The genus Ebolavirus comprises some of the deadliest viruses for primates and humans and associated disease outbreaks are increasing in Africa. Different evidence suggests that bats are putative reservoir hosts and play a major role in the transmission cycle of these filoviruses. Thus, detailed knowledge about their distribution might improve risk estimations of where future disease outbreaks might occur. A MaxEnt niche modelling approach based on climatic variables and land cover was used to investigate the potential distribution of 9 bat species associated to the Zaire ebolavirus. This viral species has led to major Ebola outbreaks in Africa and is known for causing high mortalities. Modelling results suggest suitable areas mainly in the areas near the coasts of West Africa with extensions into Central Africa, where almost all of the 9 species studied find suitable habitat conditions. Previous spillover events and outbreak sites of the virus are covered by the modelled distribution of 3 bat species that have been tested positive for the virus not only using serology tests but also PCR methods. Modelling the habitat suitability of the bats is an important step that can benefit public information campaigns and may ultimately help control future outbreaks of the disease.

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.

Experimental infection of Egyptian rousette bats (Rousettus aegyptiacus) with Sosuga virus demonstrates potential transmission routes for a bat-borne human pathogenic paramyxovirus

In August 2012, a wildlife biologist became severely ill after becoming infected with a novel paramyxovirus, termed Sosuga virus. In the weeks prior to illness, the patient worked with multiple species of bats in South Sudan and Uganda, including Egyptian rousette bats (ERBs: Rousettus aegyptiacus). A follow-up study of Ugandan bats found multiple wild-caught ERBs to test positive for SOSV in liver and spleen. To determine the competency of these bats to act as a natural reservoir host for SOSV capable of infecting humans, captive-bred ERBs were inoculated with a recombinant SOSV, representative of the patient's virus sequence. The bats were inoculated subcutaneously, sampled daily (blood, urine, fecal, oral and rectal swabs) and serially euthanized at predetermined time points. All inoculated bats became infected with SOSV in multiple tissues and blood, urine, oral, rectal and fecal swabs tested positive for SOSV RNA. No evidence of overt morbidity or mortality were observed in infected ERBs, although histopathological examination showed subclinical disease in a subset of tissues. Importantly, SOSV was isolated from oral/rectal swabs, urine and feces, demonstrating shedding of infectious virus concomitant with systemic infection. All bats euthanized at 21 days post-inoculation (DPI) seroconverted to SOSV between 16 and 21 DPI. These results are consistent with ERBs being competent reservoir hosts for SOSV with spillover potential to humans.

Exposure to Ebola Virus and Risk for Infection with Malaria Parasites, Rural Gabon

An association between malaria and risk for death among patients with Ebola virus disease has suggested within-host interactions between Plasmodium falciparum parasites and Ebola virus. To determine whether such an interaction might also influence the probability of acquiring either infection, we used a large snapshot surveillance study from rural Gabon to test if past exposure to Ebola virus is associated with current infection with Plasmodium spp. during nonepidemic conditions. We found a strong positive association, on population and individual levels, between seropositivity for antibodies against Ebola virus and the presence of Plasmodium parasites in the blood. According to a multiple regression model accounting for other key variables, antibodies against Ebola virus emerged as the strongest individual-level risk factor for acquiring malaria. Our results suggest that within-host interactions between malaria parasites and Ebola virus may underlie epidemiologic associations.

A sample-to-answer, portable platform for rapid detection of pathogens with a smartphone interface

Emerging and re-emerging infectious diseases pose global threats to human health. Although several conventional diagnostic methods have been widely adopted in the clinic, the long turn-around times of "gold standard" culture-based techniques, as well as the limited sensitivity of lateral-flow strip assays, thwart medical progress. In this study, a smartphone-controlled, automated, and portable system was developed for rapid molecular diagnosis of pathogens (including viruses and bacteria) via the use of a colorimetric loop-mediated isothermal amplification (LAMP) approach on a passive, self-driven microfluidic device. The system was capable of 1) purifying viral or bacterial samples with specific affinity reagents that had been pre-conjugated to magnetic beads, 2) lysing pathogens at low temperatures, 3) executing isothermal nucleic acid amplification, and 4) quantifying the results of colorimetric assays for detection of pathogens with an integrated color sensor. The entire, 40 min analytical process was automatically performed with a novel punching-press mechanism that could be controlled and monitored by a smartphone. As a proof of concept, the influenza A (H1N1) virus and methicillin-resistant Staphylococcus aureus bacteria were used to characterize and optimize the device, and the limits of detection were experimentally found to be 3.2 × 10^-3 hemagglutinating units (HAU) per reaction and 30 colony-forming units (CFU) per reaction, respectively; both such values represent high enough sensitivity for clinical adoption. Moreover, the colorimetric assay could be both qualitative and quantitative for detection of pathogens. This is the first instance of an easy-to-use, automated, and portable system for accurate and sensitive molecular diagnosis of either viruses or bacteria, and it is envisioned that this smartphone-controlled apparatus may serve as a platform for clinical, point-of-care pathogen detection, particularly in resource-limited settings.

Serological evidence of exposure to ebolaviruses in domestic pigs from Guinea

The genus Ebolavirus comprises several virus species with zoonotic potential and varying pathogenicity for humans. Ebolaviruses are considered to circulate in wildlife with occasional spillover events into the human population which then often leads to severe disease outbreaks. Several studies indicate a significant role of bats as reservoir hosts in the ebolavirus ecology. However, pigs from the Philippines have been found to be naturally infected with Reston virus (RESTV), an ebolavirus that is thought to only cause asymptomatic infections in humans. The recent report of ebolavirus-specific antibodies in pigs from Sierra Leone further supports natural infection of pigs with ebolaviruses. However, susceptibility of pigs to highly pathogenic Ebola virus (EBOV) was only shown under experimental settings and evidence for natural infection of pigs with EBOV is currently lacking. Between October and December 2017, we collected 308 serum samples from pigs in Guinea, West Africa, and tested for the presence of ebolavirus-specific antibodies with different serological assays. Besides reactivity to EBOV nucleoproteins in ELISA and Western blot for 19 (6.2%) and 13 (4.2%) samples, respectively, four sera recognized Sudan virus (SUDV) NP in Western blot. Furthermore, four samples specifically detected EBOV or SUDV glycoprotein (GP) in an indirect immunofluorescence assay under native conditions. Virus neutralization assay based on EBOV (Mayinga isolate) revealed five weakly neutralizing sera. The finding of (cross-) reactive and weakly neutralizing antibodies suggests the exposure of pigs from Guinea to ebolaviruses or ebola-like viruses with their pathogenicity as well as their zoonotic potential remaining unknown. Future studies should investigate whether pigs can act as an amplifying host for ebolaviruses and whether there is a risk for spillover events.

Filovirus-reactive antibodies in humans and bats in Northeast India imply zoonotic spillover

Bats are reservoirs for several zoonotic pathogens, including filoviruses. Recent work highlights the diversity of bat borne filoviruses in Asia. High risk activities at the bat-human interface pose the threat of zoonotic virus transmission. We present evidence for prior exposure of bat harvesters and two resident fruit bat species to filovirus surface glycoproteins by screening sera in a multiplexed serological assay. Antibodies reactive to two antigenically distinct filoviruses were detected in human sera and to three individual filoviruses in bats in remote Northeast India. Sera obtained from Eonycteris spelaea bats showed similar patterns of cross-reactivity as human samples, suggesting them as the species responsible for the spillover. In contrast, sera from Rousettus leschenaultii bats reacted to two different virus glycoproteins. Our results indicate circulation of several filoviruses in bats and the possibility for filovirus transmission from bats to humans.

Focused virus surveillance at human-wildlife interfaces enables proactive detection of potentially epidemic pathogens. Filoviruses, including ebolaviruses and marburgviruses, are pathogens with epidemic potential. They were previously detected in bats and have caused disease outbreaks in humans with a high case fatality rate. Here, we tested sera obtained from bats and humans at a high-risk interface for the presence of filovirus reactive antibodies. Human participants were engaged in annual bat hunts, possibly exposing them to bat-borne viruses. We report the exposure of humans to filoviruses that were likely derived from the two sampled bat species. The bats contain antibodies raised to presumably three distinct filoviruses. Our findings suggest bats in South Asia act as a reservoir host of a diverse range of filoviruses and filovirus spillover occurs through human exposure to these bats.

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.

Serological Evidence for the Circulation of Ebolaviruses in Pigs From Sierra Leone

Many human ebolavirus outbreaks have been linked to contact with wildlife including nonhuman primates and bats, which are assumed to serve as host species. However, it is largely unknown to what extent other animal species, particularly livestock, are involved in the transmission cycle or act as additional hosts for filoviruses. Pigs were identified as a susceptible host for Reston virus with subsequent transmission to humans reported in the Philippines. To date, there is no evidence of natural Ebola virus (EBOV) infection in pigs, although pigs were shown to be susceptible to EBOV infection under experimental settings. To investigate the potential role of pigs in the ecology of EBOV, we analyzed 400 porcine serum samples from Sierra Leone for the presence of ebolavirus-specific antibodies. Three samples reacted with ebolavirus nucleoproteins but had no neutralizing antibodies. Our results (1) suggest the circulation of ebolaviruses in swine in Sierra Leone that are antigenically related but not identical to EBOV and (2) could represent undiscovered ebolaviruses with unknown pathogenic and/or zoonotic potential.

Evaluation of Diagnostic Performance of Three Indirect Enzyme-Linked Immunosorbent Assays for the Detection of IgG Antibodies to Ebola Virus in Human Sera

Filovirus serological diagnosis and epidemiological investigations are hampered due to the unavailability of validated immunoassays. Diagnostic performance of three indirect enzyme-linked immunosorbent assays (I-ELISA) was evaluated for the detection of IgG antibody to Ebola virus (EBOV) in human sera. One I-ELISA was based on a whole EBOV antigen (WAg) and two utilized recombinant nucleocapsid (NP) and glycoproteins (GP), respectively. Validation data sets derived from individual sera collected in South Africa (SA), representing an EBOV non-endemic country, and from sera collected during an Ebola disease (EBOD) outbreak in Sierra Leone (SL), were categorized according to the compounded results of the three I-ELISAs and real time reverse-transcription polymerase chain reaction (RT-PCR). At the cut-off values selected at 95% accuracy level by the two-graph receiver operating characteristic analysis, specificity in the SA EBOV negative serum panel (n = 273) ranged from 98.17% (GP ELISA) to 99.27% (WAg ELISA). Diagnostic specificity in the SL EBOV negative panel (n = 676) was 100% by the three ELISAs. The diagnostic sensitivity in 423 RT-PCR confirmed EBOD patients was dependent on the time when the serum was collected after onset of disease. It significantly increased 2 weeks post-onset, reaching 100% sensitivity by WAg and NP and 98.1% by GP I-ELISA.

Disentangling serology to elucidate henipa- and filovirus transmission in Madagascar fruit bats

Bats are reservoirs for emerging human pathogens, including Hendra and Nipah henipaviruses and Ebola and Marburg filoviruses. These viruses demonstrate predictable patterns in seasonality and age structure across multiple systems; previous work suggests that they may circulate in Madagascar's endemic fruit bats, which are widely consumed as human food. We aimed to (a) document the extent of henipa- and filovirus exposure among Malagasy fruit bats, (b) explore seasonality in seroprevalence and serostatus in these bat populations and (c) compare mechanistic hypotheses for possible transmission dynamics underlying these data. To this end, we amassed and analysed a unique dataset documenting longitudinal serological henipa- and filovirus dynamics in three Madagascar fruit bat species. We uncovered serological evidence of exposure to Hendra-/Nipah-related henipaviruses in Eidolon dupreanum, Pteropus rufus and Rousettus madagascariensis, to Cedar-related henipaviruses in E. dupreanum and R. madagascariensis and to Ebola-related filoviruses in P. rufus and R. madagascariensis. We demonstrated significant seasonality in population-level seroprevalence and individual serostatus for multiple viruses across these species, linked to the female reproductive calendar. An age-structured subset of the data highlighted evidence of waning maternal antibodies in neonates, increasing seroprevalence in young and decreasing seroprevalence late in life. Comparison of mechanistic epidemiological models fit to these data offered support for transmission hypotheses permitting waning antibodies but retained immunity in adult-age bats. Our findings suggest that bats may seasonally modulate mechanisms of pathogen control, with consequences for population-level transmission. Additionally, we narrow the field of candidate transmission hypotheses by which bats are presumed to host and transmit potentially zoonotic viruses globally.

Filovirus Disease Outbreaks: A Chronological Overview

Filoviruses cause outbreaks which lead to high fatality in humans and non-human primates, thus tagging them as major threats to public health and species conservation. In this review, we give account of index cases responsible for filovirus disease outbreaks that have occurred over the past 52 years in a chronological fashion, by describing the circumstances that led to the outbreaks, and how each of the outbreaks broke out. Since the discovery of Marburg virus and Ebola virus in 1967 and 1976, respectively, more than 40 filovirus disease outbreaks have been reported; majority of which have occurred in Africa. The chronological presentation of this review is to provide a concise overview of filovirus disease outbreaks since the discovery of the viruses, and highlight the patterns in the occurrence of the outbreaks. This review will help researchers to better appreciate the need for surveillance, especially in areas where there have been no filovirus disease outbreaks. We conclude by summarizing some recommendations that have been proposed by health and policy decision makers over the years.

Comparative analysis of serologic cross-reactivity using convalescent sera from filovirus-experimentally infected fruit bats

With the exception of Reston and Bombali viruses, the marburgviruses and ebolaviruses (family Filoviridae) cause outbreaks of viral hemorrhagic fever in sub-Saharan Africa. The Egyptian rousette bat (ERB) is a natural reservoir host for the marburgviruses and evidence suggests that bats are also natural reservoirs for the ebolaviruses. Although the search for the natural reservoirs of the ebolaviruses has largely involved serosurveillance of the bat population, there are no validated serological assays to screen bat sera for ebolavirus-specific IgG antibodies. Here, we generate filovirus-specific antisera by prime-boost immunization of groups of captive ERBs with all seven known culturable filoviruses. After validating a system of filovirus-specific indirect ELISAs utilizing infectious-based virus antigens for detection of virus-specific IgG antibodies from bat sera, we assess the level of serological cross-reactivity between the virus-specific antisera and heterologous filovirus antigens. This data is then used to generate a filovirus antibody fingerprint that can predict which of the filovirus species in the system is most antigenically similar to the species responsible for past infection. Our filovirus IgG indirect ELISA system will be a critical tool for identifying bat species with high ebolavirus seroprevalence rates to target for longitudinal studies aimed at establishing natural reservoir host-ebolavirus relationships.

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.

Glycoprotein GP as a basis for the universal vaccine against Ebola virus disease

Ebola virus disease (EVD) is one of the deadliest viral infections affecting humans and nonhuman primates. Of 6 known representatives of the Ebolavirus genus responsible for the disease, 3 can infect humans, causing acute highly contagious fever characterized by up to 90% fatality. These include Bundibugyo ebolavirus (BDBV), Zaire ebolavirus (ZEBOV) and Sudan ebolavirus (SUDV). The majority of the reported EVD cases are caused by ZEBOV. Vaccine development against the virus started in 1976, immediately after the causative agent of the infection was identified. So far, 4 vaccines have been approved. All of them are based on the protective epitope of the ZEBOV glycoprotein GP. Because SUDV and BDBV can also cause outbreaks and epidemics, it is vital to design a vaccine capable of conferring protection against all known ebolaviruses posing a threat to the human population. This article presents systematized data on the structure, immunogenicity and protective properties of ebolavirus glycoprotein GP, looks closely at the immunodominant epitopes of ZEBOV, SUDV and BDBV glycoprotein GP required to elicit a protective immune response, and offers a rational perspective on the development of a universal vaccine against EVD that relies on the use of vectors expressing two variants of GP represented by ZEBOV and SUDV.

A Smartphone-Based Rapid Telemonitoring System for Ebola and Marburg Disease Surveillance

We have developed a digital and multiplexed platform for the rapid detection and telemonitoring of infections caused by Ebola and Marburg filoviruses. The system includes a flow cell assay cartridge that captures specific antibodies with microarrayed recombinant antigens from all six species of filovirus, and a smartphone fluorescent reader for high-performance interpretation of test results. Multiplexed viral proteins, which are expandable to include greater numbers of probes, were incorporated to obtain highest confidence results by cross-correlation, and a custom smartphone application was developed for data analysis, interpretation, and communication. The smartphone reader utilizes an opto-electro-mechanical hardware attachment that snaps at the back of a Motorola smartphone and provides a user interface to manage the operation, acquire test results, and communicate with cloud service. The application controls the hardware attachment to turn on LEDs and digitally record the optically enhanced images. Assay processing time is approximately 20 min for microliter amounts of blood, and test results are digitally processed and displayed within 15 s. Furthermore, a secure cloud service was developed for the telemonitoring of test results generated by the smartphone readers in the field. Assay system results were tested with sera from nonhuman primates that received a live attenuated EBOV vaccine. This integrated system will provide a rapid, reliable, and digital solution to prevent the rapid overwhelming of medical systems and resources during EVD or MVD outbreaks. Further, this disease-monitoring system will be useful in resource-limited countries where there is a need for dispersed laboratory analysis of recent or active infections.

Investigation of Outbreak-Specific Nonsynonymous Mutations on Ebolavirus GP in the Context of Known Immune Reactivity

The global response to the most recent EBOV outbreak has led to increased generation and availability of data, which can be globally analyzed to increase our understanding of immune responses to EBOV. We analyzed the published antibody epitope data to identify regions immunogenic for humans on the main GP antigenic target and determine sequence variance/nonsynonymous mutations between historical isolates and variants from the 2013-2016 outbreak. Approximately half of the GP sequence has been reported as targeted by antibody responses. Our results show an enrichment of nonsynonymous mutations (NSMs) within epitopic regions on GP (70%, p = 0.0133). Mapping NSMs to human epitope reactivity may be useful for future therapeutic and prophylaxis development as well as for our general understanding of immunity against EBOV.

Persistence of Ebola virus after the end of widespread transmission in Liberia: an outbreak report

BACKGROUND

Outbreak response efforts for the 2014-15 Ebola virus disease epidemic in west Africa brought widespread transmission to an end. However, subsequent clusters of infection have occurred in the region. An Ebola virus disease cluster in Liberia in November, 2015, that was identified after a 15-year-old boy tested positive for Ebola virus infection in Monrovia, raised the possibility of transmission from a persistently infected individual.

METHODS

Case investigations were done to ascertain previous contact with cases of Ebola virus disease or infection with Ebola virus. Molecular investigations on blood samples explored a potential linkage between Ebola virus isolated from cases in this November, 2015, cluster and epidemiologically linked cases from the 2014-15 west African outbreak, according to the national case database.

FINDINGS

The cluster investigated was the family of the index case (mother, father, three siblings). Ebola virus genomes assembled from two cases in the November, 2015, cluster, and an epidemiologically linked Ebola virus disease case in July, 2014, were phylogenetically related within the LB5 sublineage that circulated in Liberia starting around August, 2014. Partial genomes from two additional individuals, one from each cluster, were also consistent with placement in the LB5 sublineage. Sequencing data indicate infection with a lineage of the virus from a former transmission chain in the country. Based on serology and epidemiological and genomic data, the most plausible scenario is that a female case in the November, 2015, cluster survived Ebola virus disease in 2014, had viral persistence or recurrent disease, and transmitted the virus to three family members a year later.

INTERPRETATION

Investigation of the source of infection for the November, 2015, cluster provides evidence of Ebola virus persistence and highlights the risk for outbreaks after interruption of active transmission. These findings underscore the need for focused prevention efforts among survivors and sustained capacity to rapidly detect and respond to new Ebola virus disease cases to prevent recurrence of a widespread outbreak.

FUNDING

US Centers for Disease Control and Prevention, Defense Threat Reduction Agency, and WHO.

A modified anthrax toxin-based enzyme-linked immunospot assay reveals robust T cell responses in symptomatic and asymptomatic Ebola virus exposed individuals

Background

Ebola virus (EBOV) caused more than 11,000 deaths during the 2013–2016 epidemic in West Africa without approved vaccines or immunotherapeutics. Despite its high lethality in some individuals, EBOV infection can produce little to no symptoms in others. A better understanding of the immune responses in individuals who experienced minimally symptomatic and asymptomatic infection could aid the development of more effective vaccines and antivirals against EBOV and related filoviruses.

Methodology/Principle findings

Between August and November 2017, blood samples were collected from 19 study participants in Lagos, Nigeria, including 3 Ebola virus disease (EVD) survivors, 10 individuals with documented close contact with symptomatic EVD patients, and 6 control healthcare workers for a cross-sectional serosurvey and T cell analysis. The Lagos samples, as well as archived serum collected from healthy individuals living in surrounding areas of the 1976 Democratic Republic of Congo (DRC) epidemic, were tested for EBOV IgG using commercial enzyme-linked immunosorbent assays (ELISAs) and Western blots. We detected antibodies in 3 out of 3 Lagos survivors and identified 2 seropositive individuals not known to have ever been infected. Of the DRC samples tested, we detected antibodies in 9 out of 71 (12.7%). To characterize the T cell responses in the Lagos samples, we developed an anthrax toxin-based enzyme-linked immunospot (ELISPOT) assay. The seropositive asymptomatic individuals had T cell responses against EBOV nucleoprotein, matrix protein, and glycoprotein 1 that were stronger in magnitude compared to the survivors.

Conclusion/Significance

Our data provide further evidence of EBOV exposure in individuals without EVD-like illness and, for the first time, demonstrate that these individuals have T cell responses that are stronger in magnitude compared to severe cases. These findings suggest that T cell immunity may protect against severe EVD, which has important implications for vaccine development.

The 2013–2016 West African Ebola virus (EBOV) outbreak is the largest on record with over 28,000 reported symptomatic cases and more than 11,000 deaths. We developed a simple and inexpensive modified anthrax toxin-based ELISPOT assay to detect and characterize the T cell responses elicited by prior exposure to EBOV. Our data show robust T cell responses to several EBOV proteins in individuals who experienced both severe and asymptomatic EBOV infections. These results provide further evidence that EBOV transmission events can go undetected. We also show that the seropositive asymptomatic individuals have stronger T cell responses compared to survivors, which has important implications for vaccine development.

Single-Dose Trivalent VesiculoVax Vaccine Protects Macaques from Lethal Ebolavirus and Marburgvirus Challenge

Previous studies demonstrated that a single intramuscular (i.m.) dose of an attenuated recombinant vesicular stomatitis virus (rVSV) vector (VesiculoVax vector platform; rVSV-N4CT1) expressing the glycoprotein (GP) from the Mayinga strain of Zaire ebolavirus (EBOV) protected nonhuman primates (NHPs) from lethal challenge with EBOV strains Kikwit and Makona. Here, we studied the immunogenicities of an expanded range of attenuated rVSV vectors expressing filovirus GP in mice. Based on data from those studies, an optimal attenuated trivalent rVSV vector formulation was identified that included rVSV vectors expressing EBOV, Sudan ebolavirus (SUDV), and the Angola strain of Marburg marburgvirus (MARV) GPs. NHPs were vaccinated with a single dose of the trivalent formulation, followed by lethal challenge 28 days later with each of the three corresponding filoviruses. At day 14 postvaccination, a serum IgG response specific for all three GPs was detected in all the vaccinated macaques. A modest and balanced cell-mediated immune response specific for each GP was also detected in a majority of the vaccinated macaques. No matter the level of total GP-specific immune response detected postvaccination, all the vaccinated macaques were protected from disease and death following lethal challenge with each of the three filoviruses. These findings indicate that vaccination with a single dose of attenuated rVSV-N4CT1 vectors each expressing a single filovirus GP may provide protection against the filoviruses most commonly responsible for outbreaks of hemorrhagic fever in sub-Saharan Africa.IMPORTANCE The West African Ebola virus Zaire outbreak in 2013 showed that the disease was not only a regional concern, but a worldwide problem, and highlighted the need for a safe and efficacious vaccine to be administered to the populace. However, other endemic pathogens, like Ebola virus Sudan and Marburg, also pose an important health risk to the public and therefore require development of a vaccine prior to the occurrence of an outbreak. The significance of our research was the development of a blended trivalent filovirus vaccine that elicited a balanced immune response when administered as a single dose and provided complete protection against a lethal challenge with all three filovirus pathogens.

Considerations for use of Ebola vaccine during an emergency response

Vaccination against Ebola virus disease is a tool that may limit disease transmission and deaths in future outbreaks, integrated within traditional Ebola outbreak prevention and control measures. Although a licensed Ebolavirus vaccine (EV) is not yet available, the 2014-2016 West African Ebola outbreak has accelerated EV clinical trials and given public health authorities in Guinea, Liberia, and Sierra Leone experience with implementation of emergency ring vaccination. As evidence supporting the use of EV during an outbreak response has become available, public health authorities in at-risk countries are considering how to integrate EV into future emergency Ebola responses and for prevention in high-risk groups, such as healthcare workers and frontline workers (HCW/FLWs), even before an EV is licensed. This review provides an overview of Ebola epidemiology, immunology, and evidence to inform regional and country-level decisions regarding EV delivery during an emergency response and to at-risk populations before a licensed vaccine is available and beyond. Countries or regions planning to use EV will need to assess factors such as the likelihood of a future Ebolavirus outbreak, the most likely species to cause an outbreak, the availability of a safe and effective EV (unlicensed or licensed) for the affected population, capacity to implement Ebola vaccination in conjunction with standard Ebola outbreak control measures, and availability of minimum essential resources and regulatory requirements to implement emergency Ebola vaccination. Potential emergency vaccination strategies for consideration include ring or geographically targeted community vaccination, HCW/FLW vaccination, and mass vaccination. The development of guidelines and protocols for Ebola vaccination will help ensure that activities are standardized, evidence-based, and well-coordinated with overall Ebola outbreak response efforts in the future.

Antibodies from a Human Survivor Define Sites of Vulnerability for Broad Protection against Ebolaviruses

Experimental monoclonal antibody (mAb) therapies have shown promise for treatment of lethal Ebola virus (EBOV) infections, but their species-specific recognition of the viral glycoprotein (GP) has limited their use against other divergent ebolaviruses associated with human disease. Here, we mined the human immune response to natural EBOV infection and identified mAbs with exceptionally potent pan-ebolavirus neutralizing activity and protective efficacy against three virulent ebolaviruses. These mAbs recognize an inter-protomer epitope in the GP fusion loop, a critical and conserved element of the viral membrane fusion machinery, and neutralize viral entry by targeting a proteolytically primed, fusion-competent GP intermediate (GP_CL) generated in host cell endosomes. Only a few somatic hypermutations are required for broad antiviral activity, and germline-approximating variants display enhanced GP_CL recognition, suggesting that such antibodies could be elicited more efficiently with suitably optimized GP immunogens. Our findings inform the development of both broadly effective immunotherapeutics and vaccines against filoviruses.

Ecology of Filoviruses

Filoviruses can cause severe and often fatal disease in humans. To date, there have been 47 outbreaks resulting in more than 31,500 cases of human illness and over 13,200 reported deaths. Since their discovery, researchers from many scientific disciplines have worked to better understand the natural history of these deadly viruses. Citing original research wherever possible, this chapter reviews laboratory and field-based studies on filovirus ecology and summarizes efforts to identify where filoviruses persist in nature, how virus is transmitted to other animals and ultimately, what drivers cause spillover to human beings. Furthermore, this chapter discusses concepts on what constitutes a reservoir host and highlights challenges encountered while conducting research on filovirus ecology, particularly field-based investigations.

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.

Minimally Symptomatic Infection in an Ebola 'Hotspot': A Cross-Sectional Serosurvey

INTRODUCTION

Evidence for minimally symptomatic Ebola virus (EBOV) infection is limited. During the 2013-16 outbreak in West Africa, it was not considered epidemiologically relevant to published models or projections of intervention effects. In order to improve our understanding of the transmission dynamics of EBOV in humans, we investigated the occurrence of minimally symptomatic EBOV infection in quarantined contacts of reported Ebola virus disease cases in a recognized 'hotspot.'

METHODOLOGY/PRINCIPAL FINDINGS

We conducted a cross-sectional serosurvey in Sukudu, Kono District, Sierra Leone, from October 2015 to January 2016. A blood sample was collected from 187 study participants, 132 negative controls (individuals with a low likelihood of previous exposure to Ebola virus), and 30 positive controls (Ebola virus disease survivors). IgG responses to Ebola glycoprotein and nucleoprotein were measured using Alpha Diagnostic International ELISA kits with plasma diluted at 1:200. Optical density was read at 450 nm (subtracting OD at 630nm to normalize well background) on a ChroMate 4300 microplate reader. A cutoff of 4.7 U/mL for the anti-GP ELISA yielded 96.7% sensitivity and 97.7% specificity in distinguishing positive and negative controls. We identified 14 seropositive individuals not known to have had Ebola virus disease. Two of the 14 seropositive individuals reported only fever during quarantine while the remaining 12 denied any signs or symptoms during quarantine.

CONCLUSIONS/SIGNIFICANCE

By using ELISA to measure Zaire Ebola virus antibody concentrations, we identified a significant number of individuals with previously undetected EBOV infection in a 'hotspot' village in Sierra Leone, approximately one year after the village outbreak. The findings provide further evidence that Ebola, like many other viral infections, presents with a spectrum of clinical manifestations, including minimally symptomatic infection. These data also suggest that a significant portion of Ebola transmission events may have gone undetected during the outbreak. Further studies are needed to understand the potential risk of transmission and clinical sequelae in individuals with previously undetected EBOV infection.

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.

Diagnosis of Ebola Virus Disease: Past, Present, and Future

Laboratory diagnosis of Ebola virus disease plays a critical role in outbreak response efforts; however, establishing safe and expeditious testing strategies for this high-biosafety-level pathogen in resource-poor environments remains extremely challenging. Since the discovery of Ebola virus in 1976 via traditional viral culture techniques and electron microscopy, diagnostic methodologies have trended toward faster, more accurate molecular assays. Importantly, technological advances have been paired with increasing efforts to support decentralized diagnostic testing capacity that can be deployed at or near the point of patient care. The unprecedented scope of the 2014-2015 West Africa Ebola epidemic spurred tremendous innovation in this arena, and a variety of new diagnostic platforms that have the potential both to immediately improve ongoing surveillance efforts in West Africa and to transform future outbreak responses have reached the field. In this review, we describe the evolution of Ebola virus disease diagnostic testing and efforts to deploy field diagnostic laboratories in prior outbreaks. We then explore the diagnostic challenges pervading the 2014-2015 epidemic and provide a comprehensive examination of novel diagnostic tests that are likely to address some of these challenges moving forward.

Rapid detection of viral antibodies based on multifunctional Staphylococcus aureus nanobioprobes

Biosynthesis of nanoparticles inside S. aureus cells has enhanced the sensitivity of immunoassays based on the S. aureus nanoparticles. However, the current methods are limited to antigen detection by conjugating IgG antibodies on S. aureus nanoparticles. In this study, a simple way to conjugate antigens to the S. aureus nanobioparticles was developed by utilizing a cell wall binding domain (CBD) from a bacteriophage lysin PlyV12. Based on this novel design, simple agglutination tests of the IgG antibodies of Ebola virus (EBOV) nucleoprotein (NP) and Middle East Respiratory Virus (MERS) NP in rabbit sera were successfully developed by conjugating the S. aureus nanobioparticles with two fusion proteins EBOV NP- CBD and MERS NP-CBD, respectively. The conjugation was done easily by just mixing the fusion proteins with the S. aureus nanoparticles. The detection time was within 20 min without any special equipment or expertise. As far as we know, this is the first time to realize the detection of viral antibodies based on S. aureus nanoparticles.

Human Survivors of Disease Outbreaks Caused by Ebola or Marburg Virus Exhibit Cross-Reactive and Long-Lived Antibody Responses

A detailed understanding of serological immune responses to Ebola and Marburg virus infections will facilitate the development of effective diagnostic methods, therapeutics, and vaccines. We examined antibodies from Ebola or Marburg survivors 1 to 14 years after recovery from disease, by using a microarray that displayed recombinant nucleoprotein (NP), viral protein 40 (VP40), envelope glycoprotein (GP), and inactivated whole virions from six species of filoviruses. All three outbreak cohorts exhibited significant antibody responses to antigens from the original infecting species and a pattern of additional filoviruses that varied by outbreak. NP was the most cross-reactive antigen, while GP was the most specific. Antibodies from survivors of infections by Marburg marburgvirus (MARV) species were least cross-reactive, while those from survivors of infections by Sudan virus (SUDV) species exhibited the highest cross-reactivity. Based on results revealed by the protein microarray, persistent levels of antibodies to GP, NP, and VP40 were maintained for up to 14 years after infection, and survival of infection caused by one species imparted cross-reactive antibody responses to other filoviruses.

Neglected filoviruses

Eight viruses are currently assigned to the family Filoviridae Marburg virus, Sudan virus and, in particular, Ebola virus have received the most attention both by researchers and the public from 1967 to 2013. During this period, natural human filovirus disease outbreaks occurred sporadically in Equatorial Africa and, despite high case-fatality rates, never included more than several dozen to a few hundred infections per outbreak. Research emphasis shifted almost exclusively to Ebola virus in 2014, when this virus was identified as the cause of an outbreak that has thus far involved more than 28 646 people and caused more than 11 323 deaths in Western Africa. Consequently, major efforts are currently underway to develop licensed medical countermeasures against Ebola virus infection. However, the ecology of and mechanisms behind Ebola virus emergence are as little understood as they are for all other filoviruses. Consequently, the possibility of the future occurrence of a large disease outbreak caused by other less characterized filoviruses (i.e. Bundibugyo virus, Lloviu virus, Ravn virus, Reston virus and Taï Forest virus) is impossible to rule out. Yet, for many of these viruses, not even rudimentary research tools are available, let alone medical countermeasures. This review summarizes the current knowledge on these less well-characterized filoviruses.

High prevalence of IgG antibodies to Ebola virus in the Efé pygmy population in the Watsa region, Democratic Republic of the Congo

BACKGROUND

Factors related to the natural transmission of Ebola virus (EBOV) to humans are still not well defined. Results of previous sero-prevalence studies suggest that circulation of EBOV in human population is common in sub-Saharan Africa. The Efé pygmies living in Democratic Republic of the Congo are known to be exposed to potential risk factors of EBOV infection such as bush meat hunting, entry into caves, and contact with bats. We studied the pygmy population of Watsa region to determine seroprevalence to EBOV infection and possible risks factors.

METHOD

Volunteer participants (N = 300) aged 10 years or above were interviewed about behavior that may constitute risk factors for transmission of EBOV, including exposures to rats, bats, monkeys and entry into caves. Samples of venous blood were collected and tested for IgG antibody against EBOV by enzyme-linked immunosorbent assay (ELISA). The χ2-test and Fisher's exact test were used for the comparison of proportions and the Student's t-test to compare means. The association between age group and anti-EBOV IgG prevalence was analysed by a nonparametric test for trend.

RESULTS

The prevalence of anti-EBOV IgG was 18.7 % overall and increased significantly with age (p = 0.023). No association was observed with exposure to risk factors (contacts with rats, bats, monkeys, or entry into caves).

CONCLUSIONS

The seroprevalence of IgG antibody to EBOV in pygmies in Watsa region is among the highest ever reported, but it remains unclear which exposures might lead to this high infection rate calling for further ecological and behavioural studies.

Ebola virus disease: emergence, outbreak and future directions

BACKGROUND

The West African Ebola crisis of 2013-15 is the largest outbreak since Ebola was first identified; Ebola has high case fatality.

SOURCES OF DATA

Pubmed with terms 'Ebola' and 'EVD' from January 1976 to June 2015. Public domain material.

AREAS OF AGREEMENT

The emergence of Ebola virus, virology, clinical features and the major elements of the 2014 outbreak and the public health response. Ebola is only transmitted by direct contact with infected individuals (including dead bodies) and their body fluids. Methods of control in hospitals and burials, and protection of healthcare workers are well established if difficult to achieve.

AREAS OF CONTENTION

There remains uncertainty surrounding specific public health interventions and novel therapies (including vaccines). How best to reduce transmission in the community during major outbreaks remains unclear.

FUTURE DIRECTIONS

The potential of vaccine and therapeutic candidates in the event of another outbreak on this scale. .

SEARCH STRATEGY

We searched all entries on the MedLine database/PubMed from 1976-2015 with the MeSH terms 'ebola', 'EVD', 'haemorrhagic fever'. We also reviewed publically available information via institutional websites from Governmental, NGOs and news organizations pertaining to the above search terms.

Risk factors for transmission of Ebola or Marburg virus disease: a systematic review and meta-analysis

BACKGROUND

The Ebola virus disease outbreak that started in Western Africa in 2013 was unprecedented because it spread within densely populated urban environments and affected many thousands of people. As a result, previous advice and guidelines need to be critically reviewed, especially with regard to transmission risks in different contexts.

METHODS

Scientific and grey literature were searched for articles about any African filovirus. Articles were screened for information about transmission (prevalence or odds ratios especially). Data were extracted from eligible articles and summarized narratively with partial meta-analysis. Study quality was also evaluated.

RESULTS

A total of 31 reports were selected from 6552 found in the initial search. Eight papers gave numerical odds for contracting filovirus illness; 23 further articles provided supporting anecdotal observations about how transmission probably occurred for individuals. Many forms of contact (conversation, sharing a meal, sharing a bed, direct or indirect touching) were unlikely to result in disease transmission during incubation or early illness. Among household contacts who reported directly touching a case, the attack rate was 32% [95% confidence interval (CI) 26-38%]. Risk of disease transmission between household members without direct contact was low (1%; 95% CI 0-5%). Caring for a case in the community, especially until death, and participation in traditional funeral rites were strongly associated with acquiring disease, probably due to a high degree of direct physical contact with case or cadaver.

CONCLUSIONS

Transmission of filovirus is unlikely except through close contact, especially during the most severe stages of acute illness. More data are needed about the context, intimacy and timing of contact required to raise the odds of disease transmission. Risk factors specific to urban settings may need to be determined.

A Digital-Analog Microfluidic Platform for Patient-Centric Multiplexed Biomarker Diagnostics of Ultralow Volume Samples

Microfluidic diagnostic devices have the potential to transform the practice of medicine. We engineered a multiplexed digital-analog microfluidic platform for the rapid and highly sensitive detection of 3-4 biomarkers in quadruplicate in 16 independent and isolated microfluidic unit cells requiring only a single 5 μL sample. We comprehensively characterized the platform by performing single enzyme and digital immunoassays, achieving single molecule detection and measured as low as ∼10 fM (330 fg/mL) GFP in buffer and ∼12 fM GFP in human serum. We applied our integrated digital detection mechanism to multiplexed detection of 1pM anti-Ebola IgG in human serum and were able to differentiate three common Ebola strains. To ascertain that the device can be applied in environments beyond clinical point-of-care settings, we developed a low-cost, portable hardware system to control and read out the microfluidic device and detected anti-Ebola IgG in ultralow volume whole blood samples to levels of 100 pM in a multiplexed assay format.

Cross-Reactive and Potent Neutralizing Antibody Responses in Human Survivors of Natural Ebolavirus Infection

Recent studies have suggested that antibody-mediated protection against the Ebolaviruses may be achievable, but little is known about whether or not antibodies can confer cross-reactive protection against viruses belonging to diverse Ebolavirus species, such as Ebola virus (EBOV), Sudan virus (SUDV), and Bundibugyo virus (BDBV). We isolated a large panel of human monoclonal antibodies (mAbs) against BDBV glycoprotein (GP) using peripheral blood B cells from survivors of the 2007 BDBV outbreak in Uganda. We determined that a large proportion of mAbs with potent neutralizing activity against BDBV bind to the glycan cap and recognize diverse epitopes within this major antigenic site. We identified several glycan cap-specific mAbs that neutralized multiple ebolaviruses, including SUDV, and a cross-reactive mAb that completely protected guinea pigs from the lethal challenge with heterologous EBOV. Our results provide a roadmap to develop a single antibody-based treatment effective against multiple Ebolavirus infections.