Why is the ebola virus so intense now?

Why is the ebola virus so intense now?

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So i'm looking into the ebola crisis and it seems the death toll is really getting crazy. I understand that it's a cytomegalovirus and that it basically overwhelms the immune system due to it's size and virulence but why is it so bad now? What has changed about it?

The folks at the Dallas hospital were said to have 'broken protocol' but to me it seems the virus may be more infectious this time around. Has it changed? Mutated?

The answer here lies in epidemiology and the pathogenic nature of the virus. Humans infected with Ebola have a range of recovery rates of 5-75%, meaning that most of those infected will not survive infection. Given the combination of preparedness factors at first recognizing a true outbreak in Ebola and viral load which had already been spread by the point healthcare workers have organized an efficient response, it is not surprising that some outbreaks are worse than others. I think attempting to correlate the virulence to the type, size with the extent of the viral spread is not pertinent, but rather, as you mentioned breaking "protocol" can have more deleterious effect than simply explaining it by a mutation.

That is not to say that this strain of Ebola is not different from those detected in other outbreaks--in fact it is likely to be quite different and accumulated several mutations.

Ebola Virus Disease (EVD)

Ebola virus (EBOV) VP40 is a major driving force of nascent virion production and a negative regulator of genome replication/transcription. Here, we showed that the YIGL sequence at the C-terminus of EBOV VP40 is important for virus-like particle (VLP) production and the regulation of genome replication/transcription. Accordingly, a mutation in the YIGL sequence caused defects in VLP production and genome replication/transcription. The residues I293 and L295 in the YIGL sequence were particularly critical for VLP production. Furthermore, an in silico analysis indicated that the amino acids surrounding the YIGL sequence contribute to intramolecular interactions within VP40. Among those surrounding residues, F209 was shown to be critical for VLP production. These results suggested that the VP40 YIGL sequence regulates two different viral replication steps, VLP production and genome replication/transcription, and the nearby residue F209 influences VLP production.

ICTV Virus Taxonomy Profile: Filoviridae

Members of the family Filoviridae produce variously shaped, often filamentous, enveloped virions containing linear non-segmented, negative-sense RNA genomes of 15–19 kb. Several filoviruses (e.g., Ebola virus) are pathogenic for humans and are highly virulent. Several filoviruses infect bats (e.g., Marburg virus), whereas the hosts of most other filoviruses are unknown. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on Filoviridae, which is available at

Assessment of the function and intergenus-compatibility of Ebola and Lloviu virus proteins

Sequences for Lloviu virus (LLOV), a putative novel filovirus, were first identified in Miniopterus schreibersii bats in Spain following a massive bat die-off in 2002, and also recently found in bats in Hungary. However, until now it is unclear if these sequences correspond to a fully functional, infectious virus, and whether it will show a pathogenic phenotype like African filoviruses, such as ebola- and marburgviruses, or be apathogenic for humans, like the Asian filovirus Reston virus. Since no infectious virus has been recovered, the only opportunity to study infectious LLOV is to use a reverse genetics-based full-length clone system to de novo generate LLOV. As a first step in this process, and to investigate whether the identified sequences indeed correspond to functional viral proteins, we have developed life cycle modelling systems for LLOV, which allow us to study genome replication and transcription as well as entry of this virus. We show that all LLOV proteins fulfill their canonical role in the virus life cycle as expected based on the well-studied related filovirus Ebola virus. Further, we have analysed the intergenus-compatibility of proteins that have to act in concert to facilitate the virus life cycle. We show that some but not all proteins from LLOV and Ebola virus are compatible with each other, emphasizing the close relationship of these viruses, and informing future studies of filovirus biology with respect to the generation of genus-chimeric proteins in order to probe virus protein–protein interactions on a functional level.

Generation, lyophilisation and epitope modification of high titre filovirus pseudotyped lentiviruses for use in antibody neutralisation assays and ELISA

The 2014–2016 Ebola outbreak in West Africa highlighted the need for improved diagnostics, surveillance and therapeutics for filoviruses. The need for high containment virus handling facilities creates a bottleneck hindering research efforts. A safe alternative to working with native viruses are pseudotyped viruses (PV) which are non-replicating particles bearing surface glycoprotein(s) that can be used for antibody detection. The aim of this study was to create a diagnostic tool to distinguish between genera and species of pathogenic filoviruses (e.g. neutralization tests and ELISA), avoiding the cross reactivity currently seen. High titre PVs bearing the receptor glycoprotein (GP) of different filovirus species, plus specific epitope chimeras, were successfully generated. Next, lyophilisation studies to assess particle stability/degradation transportation and long-term storage were conducted. Filoviruses maintained their titres for at least 1.5 years after lyophilisation when kept in temperatures of up to 4 °C, with all filovirus genera following a similar trend. At higher temperatures, PVs degraded to unworkable titres. Reconstituted PVs also performed well in neutralisation assays. A chimeric cuevavirus GP bearing ebolavirus (Zaire sp.) epitopes KZ52 and 1 H3 retained infectivity, with average titres of approximately 1×10 7 RLU ml −1 , similar to wild type, indicating its structure was not compromised. These chimeras are now being assessed in neutralisation tests using specific monoclonal antibodies and incorporated into ELISA with PVs as antigens. The data suggests lyophilised PVs are amenable to long-term storage, and their GPs can be modified to create artificial antigens for diagnostics and serosurveillance.

How myeloid cells contribute to the pathogenesis of prominent emerging zoonotic diseases

Up to 75 % of emerging human diseases are zoonoses, spread from animals to humans. Although bacteria, fungi and parasites can be causative agents, the majority of zoonotic infections are caused by viral pathogens. During the past 20 years many factors have converged to cause a dramatic resurgence or emergence of zoonotic diseases. Some of these factors include demographics, social changes, urban sprawl, changes in agricultural practices and global climate changes. In the period between 2014–2017 zoonotic viruses including ebola virus (EBOV), chikungunya virus (CHIKV), dengue virus (DENV) and zika virus (ZIKV), caused prominent outbreaks resulting in significant public health and economic burdens, especially in developing areas where these diseases are most prevalent. When a viral pathogen invades a new human host, it is the innate immune system that serves as the first line of defence. Myeloid cells are especially important to help fight viral infections, including those of zoonotic origins. However, viruses such as EBOV, CHIKV, DENV and ZIKV have evolved mechanisms that allow circumvention of the host’s innate immune response, avoiding eradication and leading to severe clinical disease. Herein, the importance of myeloid cells in host defence is discussed and the mechanisms by which these viruses exploit myeloid cells are highlighted. The insights provided in this review will be invaluable for future studies looking to identify potential therapeutic targets towards the treatment of these emerging diseases.

Ebola returns to its Congo Basin heartland

Immunogenicity of propagation-restricted vesicular stomatitis virus encoding Ebola virus glycoprotein in guinea pigs

Vesicular stomatitis virus (VSV) expressing the Ebola virus (EBOV) glycoprotein (GP) in place of the VSV glycoprotein G (VSV/EBOV-GP) is a promising EBOV vaccine candidate which has already entered clinical phase 3 studies. Although this chimeric virus was tolerated overall by volunteers, it still caused viremia and adverse effects such as fever and arthritis, suggesting that it might not be sufficiently attenuated. In this study, the VSV/EBOV-GP vector was further modified in order to achieve attenuation while maintaining immunogenicity. All recombinant VSV constructs were propagated on VSV G protein expressing helper cells and used to immunize guinea pigs via the intramuscular route. The humoral immune response was analysed by EBOV-GP-specific fluorescence-linked immunosorbent assay, plaque reduction neutralization test and in vitro virus-spreading inhibition test that employed recombinant VSV/EBOV-GP expressing either green fluorescent protein or secreted Nano luciferase. Most modified vector constructs induced lower levels of protective antibodies than the parental VSV/EBOV-GP or a recombinant modified vaccinia virus Ankara vector encoding full-length EBOV-GP. However, the VSV/EBOV-GP(F88A) mutant was at least as immunogenic as the parental vaccine virus although it was highly propagation-restricted. This finding suggests that VSV-vectored vaccines need not be propagation-competent to induce a robust humoral immune response. However, VSV/EBOV-GP(F88A) rapidly reverted to a fully propagation-competent virus indicating that a single-point mutation is not sufficient to maintain the propagation-restricted phenotype.

Different effects of two mutations on the infectivity of Ebola virus glycoprotein in nine mammalian species

Ebola virus (EBOV), which belongs to the genus Ebolavirus , causes a severe and often fatal infection in primates, including humans, whereas Reston virus (RESTV) only causes lethal disease in non-human primates. Two amino acids (aa) at positions 82 and 544 of the EBOV glycoprotein (GP) are involved in determining viral infectivity. However, it remains unclear how these two aa residues affect the infectivity of Ebolavirus species in various hosts. Here we performed viral pseudotyping experiments with EBOV and RESTV GP derivatives in 10 cell lines from 9 mammalian species. We demonstrated that isoleucine at position 544/545 increases viral infectivity in all host species, whereas valine at position 82/83 modulates viral infectivity, depending on the viral and host species. Structural modelling suggested that the former residue affects viral fusion, whereas the latter residue influences the interaction with the viral entry receptor, Niemann–Pick C1.

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 .

Chloroquine inhibited Ebola virus replication in vitro but failed to protect against infection and disease in the in vivo guinea pig model

Ebola virus (EBOV) is highly pathogenic, with a predisposition to cause outbreaks in human populations accompanied by significant mortality. Owing to the lack of approved therapies, screening programmes of potentially efficacious drugs have been undertaken. One of these studies has demonstrated the possible utility of chloroquine against EBOV using pseudotyped assays. In mouse models of EBOV disease there are conflicting reports of the therapeutic effects of chloroquine. There are currently no reports of its efficacy using the larger and more stringent guinea pig model of infection. In this study we have shown that replication of live EBOV is impaired by chloroquine in vitro . However, no protective effects were observed in vivo when EBOV-infected guinea pigs were treated with chloroquine. These results advocate that chloroquine should not be considered as a treatment strategy for EBOV.

The 2014 Ebola virus disease outbreak in West Africa

On 23 March 2014, the World Health Organization issued its first communiqué on a new outbreak of Ebola virus disease (EVD), which began in December 2013 in Guinée Forestière (Forested Guinea), the eastern sector of the Republic of Guinea. Located on the Atlantic coast of West Africa, Guinea is the first country in this geographical region in which an outbreak of EVD has occurred, leaving aside the single case reported in Ivory Coast in 1994. Cases have now also been confirmed across Guinea as well as in the neighbouring Republic of Liberia. The appearance of cases in the Guinean capital, Conakry, and the transit of another case through the Liberian capital, Monrovia, presents the first large urban setting for EVD transmission. By 20 April 2014, 242 suspected cases had resulted in a total of 147 deaths in Guinea and Liberia. The causative agent has now been identified as an outlier strain of Zaire Ebola virus. The full geographical extent and degree of severity of the outbreak, its zoonotic origins and its possible spread to other continents are sure to be subjects of intensive discussion over the next months.

Coronaviruses in bats from Mexico

Bats are reservoirs for a wide range of human pathogens including Nipah, Hendra, rabies, Ebola, Marburg and severe acute respiratory syndrome coronavirus (CoV). The recent implication of a novel beta (β)-CoV as the cause of fatal respiratory disease in the Middle East emphasizes the importance of surveillance for CoVs that have potential to move from bats into the human population. In a screen of 606 bats from 42 different species in Campeche, Chiapas and Mexico City we identified 13 distinct CoVs. Nine were alpha (α)-CoVs four were β-CoVs. Twelve were novel. Analyses of these viruses in the context of their hosts and ecological habitat indicated that host species is a strong selective driver in CoV evolution, even in allopatric populations separated by significant geographical distance and that a single species/genus of bat can contain multiple CoVs. A β-CoV with 96.5 % amino acid identity to the β-CoV associated with human disease in the Middle East was found in a Nyctinomops laticaudatus bat, suggesting that efforts to identify the viral reservoir should include surveillance of the bat families Molossidae/Vespertilionidae, or the closely related Nycteridae/Emballonuridae. While it is important to investigate unknown viral diversity in bats, it is also important to remember that the majority of viruses they carry will not pose any clinical risk, and bats should not be stigmatized ubiquitously as significant threats to public health.

Novel mutations in Marburg virus glycoprotein associated with viral evasion from antibody mediated immune pressure

Marburg virus (MARV) and Ebola virus, members of the family Filoviridae , cause lethal haemorrhagic fever in humans and non-human primates. Although the outbreaks are concentrated mainly in Central Africa, these viruses are potential agents of imported infectious diseases and bioterrorism in non-African countries. Recent studies demonstrated that non-human primates passively immunized with virus-specific antibodies were successfully protected against fatal filovirus infection, highlighting the important role of antibodies in protective immunity for this disease. However, the mechanisms underlying potential evasion from antibody mediated immune pressure are not well understood. To analyse possible mutations involved in immune evasion in the MARV envelope glycoprotein (GP) which is the major target of protective antibodies, we selected escape mutants of recombinant vesicular stomatitis virus (rVSV) expressing MARV GP (rVSVΔG/MARVGP) by using two GP-specific mAbs, AGP127-8 and MGP72-17, which have been previously shown to inhibit MARV budding. Interestingly, several rVSVΔG/MARVGP variants escaping from the mAb pressure-acquired amino acid substitutions in the furin-cleavage site rather than in the mAb-specific epitopes, suggesting that these epitopes are recessed, not exposed on the uncleaved GP molecule, and therefore inaccessible to the mAbs. More surprisingly, some variants escaping mAb MGP72-17 lacked a large proportion of the mucin-like region of GP, indicating that these mutants efficiently escaped the selective pressure by deleting the mucin-like region including the mAb-specific epitope. Our data demonstrate that MARV GP possesses the potential to evade antibody mediated immune pressure due to extraordinary structural flexibility and variability.

Lethality and pathogenesis of airborne infection with filoviruses in A129 α/β −/− interferon receptor-deficient mice

Normal immunocompetent mice are not susceptible to non-adapted filoviruses. There are therefore two strategies available to establish a murine model of filovirus infection: adaptation of the virus to the host or the use of genetically modified mice that are susceptible to the virus. A number of knockout (KO) strains of mice with defects in either their adaptive or innate immunity are susceptible to non-adapted filoviruses. In this study, A129 α/β −/− interferon receptor-deficient KO mice, strain A129 IFN-α/β −/−, were used to determine the lethality of a range of filoviruses, including Lake Victoria marburgvirus (MARV), Zaire ebolavirus (ZEBOV), Sudan ebolavirus (SEBOV), Reston ebolavirus (REBOV) and Côte d’Ivoire ebolavirus (CIEBOV), administered by using intraperitoneal (IP) or aerosol routes of infection. One hundred percent mortality was observed in all groups of KO mice that were administered with a range of challenge doses of MARV and ZEBOV by either IP or aerosol routes. Mean time to death for both routes was dose-dependent and ranged from 5.4 to 7.4 days in the IP injection challenge, and from 10.2 to 13 days in the aerosol challenge. The lethal dose (50 % tissue culture infective dose, TCID 50 ) of ZEBOV for KO mice was 50 ml −1 when administered by either the IP or aerosol route of infection for MARV the lethal dose was 50 ml −1 by the IP route of infection and 50 ml −1 by the aerosol route. In contrast, there was no mortality after infection with SEBOV or REBOV by either IP or aerosol routes of infection all the mice lost weight (

15 % loss of group mean body weight with SEBOV and

7 % with REBOV) but recovered to their original weights by day 14 post-challenge. There was no mortality in mice administered with CIEBOV via the IP route of infection and no clinical signs of infection were observed. The progression of disease was faster following infection with ZEBOV than with MARV but ultimately both viruses caused widespread infection with high titres of the infectious viruses in multiple organs. Histopathological observations were consistent with other animal models and showed widespread organ damage. This study suggests that MARV and ZEBOV are more virulent when administered via the IP route rather than by aerosol infection, although both are highly virulent by either route. The KO mouse may provide a useful model to test potential antiviral therapeutics against wild-type filoviruses.

Genus-specific recruitment of filovirus ribonucleoprotein complexes into budding particles

The filoviral matrix protein VP40 orchestrates virus morphogenesis and budding. To do this it interacts with both the glycoprotein (GP 1,2 ) and the ribonucleoprotein (RNP) complex components however, these interactions are still not well understood. Here we show that for efficient VP40-driven formation of transcription and replication-competent virus-like particles (trVLPs), which contain both an RNP complex and GP 1,2 , the RNP components and VP40, but not GP 1,2 and VP40, must be from the same genus. trVLP preparations contained both spherical and filamentous particles, but only the latter were able to infect target cells and to lead to genome replication and transcription. Interestingly, the genus specificity of the VP40–RNP interactions was specific to the formation of filamentous trVLPs, but not to spherical particles. These results not only further our understanding of VP40 interactions, but also suggest that special care is required when using trVLP or VLP systems to model virus morphogenesis.

The Ebola Outbreak and Biological Patents

Even though the United States has been declared “Ebola-free”, the effort to contain and eradicate Ebola hemorrhagic fever from the affected African countries of Sierra Leone, Liberia, Guinea, and now Mali is ongoing. As the fight has evolved over the past year, misconceptions and conspiracies have made their way to the general public. This time of misinformation can hurt scientific and medical advances necessary to combat the disease..

Early in the Fall of this year, while most in the United States were becoming more aware of the outbreak occurring in West Africa, and with several cases were starting to pop up here within our borders, some started spreading the conspiracies and misinformation regarding a patent issued by the U.S. Patent and Trademark Office (USPTO) to the Center for Disease Control. There is in fact a U.S. patent that was published in 2010 (Patent No. CA2741523A1) for a particular strain of Ebola virus isolated in 2007 from Bundibugyo, Uganda. In this patent, it is known as Bundibugyo ebolavirus (EboBun), and is a very close relative to the species of Ebola virus, known as Ebola Zaire, that is causing the current outbreak.

Suddenly, there were stories on social media about how the government is using the virus as a form of population control. There were even news stories of well-respected people in many communities speaking out about how the Ebola virus was man made and the patent was going to be used to control who had access and who could make vaccines. Basically, many thought it to be a money making scheme by the CDC and the Department of Health and Human Services (DHHS). Many were jumping on the actual language of the patent, where it states that the virus is an “invention”, and this demonstrated once and for all that the government had invented the deadly virus.

Biological patents have been controversial ever since the first one in the U.S. was issued in 1906 for a purified form of adrenaline. This was challenged, but upheld, arguing that the purified form of a natural substance was more useful than the original. Since then, researchers and companies have been patenting DNA sequences, genetically modified organisms, as well as entire genomes. It is thought that more than 2,000 patents for biological materials have been awarded in the U.S.. When there is a patent for a particular “invention” or discovery, one might ask, “At what cost to valuable research?” A patent to many implies that money must be exchanged when a material is used, or when a vaccine or treatment is discovered, one must pay the original inventor. If not, then this could be an infringement of the patent and could be taken to court through a legal process called patent litigation.

As of June 2013, the Supreme Court ruled that companies or groups of individuals cannot patent isolated genetic material, which includes viruses, in the famous Association For Molecular Pathology v. Myriad Genetics case. Myriad Genetics held patents obtained in the 1990s for the two genes shown to be crucial in the development of hereditary breast cancer, BRCA1 and BRCA2. The company believes that because the genes they patented have been isolated and modified so that they are useful in a laboratory setting, they are open to being patented. They are, as Myriad states, human inventions very different from the naturally occurring genes found in the human genome. Since the patenting of the genes, Myriad has held the monopoly for research on detection of hereditary breast and ovarian cancers.

The Department of Justice has stated that the changes made on which Myriad based their patent was insignificant because what is important to researchers and doctors is the actual information in the gene, not the composition of the gene. Patients and advocates also complained that because of the patents Myriad holds, research is hindered and genetic testing is expensive and not as readily available.

While the system is not perfect due to large companies seeking compensation for services that they have developed and patented, the fact that there are biological patents at all is not a bad thing as a whole. The Myriad Genetics Supreme Court case is an example of why government agencies such as the CDC and the DHHS seek patents. It is not uncommon for the CDC to patent living organisms so that necessary research may continue without restrictions by companies. A patent obtained by the government allows scientists to work on biological organisms without a fee and allows for open access to these materials. This is why there is a biological patent on the Ebola virus species that was found in Uganda in 2007 so that when there is a crisis such as the one in which we find ourselves currently, many researchers have access to what is currently known about the virus, and can work together to find a cure. We are also in an exciting time in biotechnology, when scientists can create new DNA sequences and synthetic organisms in the lab. This research can help us understand the creation of life and other biological processes, and this should be protected.

Trying to educate the general public about things such as the current research towards eradicating diseases or about the patents issued to protect the intellectual property of researchers, universities, and government agencies is a challenging, but important task. In the age of social media where ideas are exchanged with ease, misinformation is rampant. Unfortunately, this can hinder scientific progress at times. Since people are unsure of where government money or their own donations go, it could lead to funding cuts from both the government and from valuable non-profit organizations. In order to move forward in our fight against disease, the public should be included in important discoveries and the process that is required to make these advances.

How Does Ebola Invade a Host?

The deadly Ebola virus contains a single strand of genetic material called RNA. Each gene in the strand serves as a blueprint to make proteins, which embed onto the surface of the membrane. One of these is the glycoprotein gene. This gene codes for two membrane proteins: the spike glycoprotein and the secreted glycoprotein.

The Ebola virus invades immune cells, such as this illustrated version of a monocyte white blood cell.

Like all viruses, Ebola needs to hijack a host cell in order to survive and replicate. The spike glycoprotein, a protein with an attached carbohydrate, helps the virus enter and infect host cells. The secreted glycoprotein acts as a decoy: it lures the immune system’s attention away from the spike glycoprotein. The immune system starts producing antibodies to fight the secreted glycoprotein, while the spike glycoprotein continues to sneak the virus into cells. Thus, the Ebola virus keeps the immune system guessing while the infection grows stronger.

Study shows how ebola becomes lethal as it spreads

Scientists investigated why Ebola virus is so deadly when it spreads from animals to humans and then from human-to-human contact. The research team looked at the Zaire Ebola strain in an animal system to understand how it gains strength. This virus is responsible for the current outbreak in West Africa.

They found that initially the animal systems were not affected by the virus, but subsequent transmission into other animals caused the virus to 'hot up' and become more severe.

The team analysed the viruses at different stages and were able to identify several changes in its genetic material that were associated with increased disease.

Professor Julian Hiscox, who led the study from the University's Institute of Infection and Global Health, explains: "The work tells us that the evolutionary goal of Ebola virus is to become more lethal.

"We were able to show through genetic analysis which parts of the virus are involved in this process. The information we have gathered will now allow us to monitor for such changes in an outbreak as well as develop future treatment strategies."

Professor Roger Hewson, leading the study from Public Health England, Porton Down, said: "Ebola virus is such a devastating infection to the people affected by the disease and the economy of West Africa.

"Our understanding of Ebola virus biology is way behind that of other viruses and our collaboration shows how we can bring together our specialists skills to close this knowledge gap."

Professor Miles Carroll, a co-author of the work, said: "This study has allowed the team to be at the forefront of developing methodologies to analyse patient samples recently taken by the European Mobile Laboratory from West Africa to understand disease evolution during the current outbreak"

Since Ebola virus was first identified more than 30 years ago, tremendous progress has been made in understanding the molecular biology and pathogenesis of this virus. However, the means by which Ebola virus is maintained and transmitted in nature remains unclear despite dedicated efforts to answer these questions. Recent work has provided new evidence that fruit bats might have a role as a reservoir species, but it is not clear whether other species are also involved or how transmission to humans or apes takes place. Two opposing hypotheses for Ebola emergence have surfaced one of long-term local persistence in a cryptic and infrequently contacted reservoir, versus another of a more recent introduction of the virus and directional spread through susceptible populations. Nevertheless, with the increasing frequency of human filovirus outbreaks and the tremendous impact of infection on the already threatened great ape populations, there is an urgent need to better understand the ecology of Ebola virus in nature.

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Immune shutdown

Another gene that's somewhat more intriguing is called VP35. This protein functions to help the virus evade an immune response. The body's immune system consists of two parts that work cooperatively. The one we mostly learn about, acquired immunity, involves antibodies and other specialized receptors that recognize specific infectious agents. Acquired immunity is the whole reason vaccines work. But this takes a while to get up to speed when a pathogen has never been encountered before.

To help protect the body at that point in the infection, cells rely on what's called the innate immune system. This isn't specific to any particular pathogen, but instead this recognizes features that are common to many pathogens, like sugars or lipids made by bacteria. Many viruses carry a protein that helps shut the innate immune system down, and Ebola is no exception. That task is handled by VP35.

"Ebola happens to have a protein that antagonizes innate immunity, and most viruses must have one of those, so it's not really unusual," Racaniello told Ars. "The innate response is so powerful that, if a virus doesn't have something to counter it, it's going to be wiped out pretty quickly."

In Ebola's case, VP35 does several things to tone down innate immunity. It binds to and inactivates some proteins involved in this response. It also blocks a branch of the innate immune system that recognizes double-stranded RNA. While these are a necessary part of the replication of single-stranded RNA viruses, they're not normally produced in the cell in any great quantities, so it's a useful way of identifying when a viral infection may be in progress. Research suggests that VP35 handles its task via a very simple route: it binds to double-stranded RNA and hides it from the innate immune system.

Partly as a consequence of this, the innate immune system doesn't trigger the production of immune signaling molecules called interferons. These interferons normally help marshal specialized immune cells and can boost the adaptive immune response.

Reality Check: How People Catch Ebola, And How They Don't

This article is more than 6 years old. Dr. Elke Muhlberger (Courtesy of Kalman Zabarsky for BU Photography)

It's confusing. You hear that Ebola victim Thomas Eric Duncan was so contagious that two Dallas nurses in protective gear caught the virus. But then you hear, in more recent days, that apparently nobody else did, including the inner circle who lived with him and cared for him. The CDC announced today that all of Mr. Duncan's "community contacts" have completed their 21-day monitoring period without developing Ebola.

How to understand that? And how to address alarmists' claims that for the nurses and so many West Africans to have caught Ebola, it must have gone "airborne"?

I turned to Dr. Elke Muhlberger, an Ebola expert long intimate with the virus &mdash through more than 20 years of Ebola research that included two pregnancies. (I must say I find this the ultimate antidote for the fear generated by the nurses' infections: A researcher so confident in the power of taking the right precautions that she had no fear &mdash and rightly so, it turned out &mdash for her babies-to-be.)

Dr. Muhlberger is an associate professor of micriobiology at Boston University and director of the Biomolecule Production Core at the National Emerging Infectious Diseases Laboratories (widely referred to as the NEIDL, pronounced "needle") at Boston University. Our conversation, lightly edited:

Is it really true you worked on Ebola through two pregnancies?

Yes, but in the proper protective gear. That makes a huge difference, if you're protected, if you know how to protect yourself, and that is the case in a Biosafety Level 4 lab, of course. If you compare the protective gear we're wearing in a Biosafety Level 4 lab and the gear they're wearing in West Africa now treating patients, it's like comparing a stainless steel vault to a cardboard box.

But on the other hand, if you look at the nurses in Dallas, you say, 'How did they get infected?' It makes you worry that maybe protective gear isn't good enough &mdash but you're proof of the opposite.

A Biosafety Level 4 lab is such a high-end lab, it is not possible to use protective gear like that in every hospital in the U.S.

Could you please lay out a brief primer on the biology of how Ebola is transmitted?

We know from previous outbreaks, and also from the current outbreak, that Ebola is transmitted by having very close contact to infected patients. So we know that it is transmitted by bodily fluids, which include blood, first of all &mdash because the amount of virus in the blood is very, very high, especially at late stages of infection &mdash but it’s also spread by vomit, by sputum, by feces, by urine and by other bodily fluids.

The reason for that is that at late stages of infection, the Ebola virus affects almost all our organs &mdash it causes a systemic infection. One main organ targeted by Ebola virus is the liver, and that could be one of the reasons that we see these very high concentrations of viral particles in the blood. But I would like to emphasize that that occurs late in infection.

Early infection is the other way around. The primary targets &mdash the first cells that come in contact with Ebola virus and get infected &mdash are cells that are part of our immune system. And these cells most likely spread the virus throughout our body. But there are not so many cells infected at the very beginning of the infection, which might be the reason why Ebola virus patients do not spread virus at the very beginning of infection. And that's why it’s safe to have contact with these patients, because the viral titers in their blood are so low that we cannot even detect them with methods like PCR, which is one of the methods we use to diagnose Ebola virus.

Is a virus only contagious when it reaches a certain level of "titer" or load?

That’s very difficult to answer because we know that for some viral infections most likely one viral particle is enough to infect somebody. So then the answer would be no. But we also know that some viruses are not really good spreaders, so you do need a certain amount of viruses to transmit this virus to another person.

Is that true for Ebola?

For Ebola virus, it seems to be true, because from experience, we know that this virus is not transmitted early in infection. If the viral titers are very low, if you’re not able to detect free viruses in the blood, then it seems Ebola virus is not transmitted to other people. Which is very good because, theoretically, that makes it really easy to control Ebola virus infection. And the reason why we have such a disaster right now, with almost 10,000 infected in West Africa and more than 4,000 already dead, is not so much the transmissibility of Ebola but rather the lack of infrastructure in these countries.

Some people are claiming that to infect so many people, the virus must have moved from just bodily fluids to "airborne".

I think there's some confusion here. We know that some viruses &mdash like influenza virus, and measles &mdash are transmitted before the patient shows symptoms. Especially the measles virus, which is the winner in terms of being contagious. What these viruses do is infect the respiratory tract &mdash that is their first target organ. That’s how they start the infection, and then they replicate or amplify themselves in cells of the upper respiratory tract. And then when we breathe, we release these viruses because they're part of our 'breathing air.' There are tiny, tiny, tiny little droplets, and these droplets contain the virus. They can stretch pretty far, like a couple of feet. And that is what we call an airborne infection. If we breathe and then we shed virus with our breath.

So you don’t even need visible droplets, it’s just air?

They’re tiny little droplets in our breath. And these viral particles are part of it. This is completely different from Ebola virus. First of all, Ebola virus does not begin an infection by infecting our upper respiratory tract. The route of infection starts with little lesions in our skin, and then the virus gets in our skin, and then in our blood system, and then in these immune cells I mentioned before, which are the primary target cells. It’s also able to get into our eyes and mucosal membranes, but it does not infect the cells which we need to get infected to have an infection be airborne. Late in the infection, when the Ebola virus patients have very high viral loads, they are really really ill, way too ill to get on a train and sit there.

So you’re saying that when they’re so ill that it could be in the respiratory system, they're super-ill, not able to go anywhere?

Exactly. The cells in the lung can be infected by Ebola virus but really late in the infection. That's very important. As far as we know, the infection starts with the immune cells &mdash for those who know a little more about the immune system, it’s dendritic cells and macrophages. Then it goes to lymph nodes. Then very quickly to the liver, and there it goes crazy. The liver is very crucial in Ebola virus infections because it is so heavily affected. Ebola virus also spreads to the spleen, to other organs, and then later in infection it tends to infect the cells that coat the blood vessels, and of course we have these cells in the lung as well.

So when we are infected with Ebola virus and we are really sick, then we spread the virus through all our body fluids, which includes blood, sputum, feces urine, breast milk and semen. Again, then we have Ebola virus in little droplets, which is the reason we talk about infection via droplets, but these droplets are much bigger &mdash though they are tiny, of course &mdash but these are much bigger than the droplets which cause aerosol-borne disease. So it’s a matter of size. And if they are bigger they cannot be transmitted over a large distance.

So if they’re bigger they can’t just float in your breath? But you could perhaps project them?

Of course you have them in your sputum &mdash as you speak, you kind of shed virus &mdash but then the droplets drop to the ground pretty quickly because they are heavier. It's really a matter of size and weight.

The CDC recently tweeted an answer to a common Ebola question: It said yes, if someone with Ebola sneezes on you and the droplets land in your eyes or mouth, then conceivably you could catch Ebola. But that doesn't count as airborne?

Exactly, and it’s all about timing. When someone is infected with measles and then sneezes or coughs, and is not sick at this point, they can transmit the virus to others and you're not even aware that someone with the disease is contacting you. That’s the big difference with Ebola virus and these bigger droplets &mdash but nevertheless droplets, of course. When Ebola virus patients start to transmit the virus, they have already developed a fever and are obviously sick.

So that helps explains why more people haven’t been infected in the U.S.?

Exactly. It's very unfortunate, what happened in Dallas &mdash that's already the worst-case scenario for the U.S. It already happened to us. First, the patient came into the country without being identified as infected. That could happen again, just because of travel activity. Also, if the outbreak in West Africa is not controlled, more and more people will become infected. This makes it likely that infected patients will get into other countries. So that was the first thing that happened, which most likely is not easy to avoid.

Second &mdash and this is something that could have been avoided &mdash is that the infected person was not quarantined immediately, though we knew he had already gotten sick. He had contact with other persons who were not protected during his illness.

Finally, the nurses, who contracted the virus from the patient and eventually became ill, were not immediately quarantined and could have infected more people. And that is the worst-case scenario we can think of with Ebola virus.

Although what's interesting is that, at least so far, aside from the two nurses, none of the people around Thomas Eric Duncan or the nurses has caught it.

Exactly. And that's exactly what we know about Ebola virus: You really need close contact, especially contact with those who are severely ill, and that is because of of this special mode of transmission. Even early in infection it is not so contagious. Those who are at risk to get infected are those who take care of the ill patients &mdash health care workers or relatives at home &mdash and then the second group who got really hard hit by Ebola virus infections is those who care for the deceased, like relatives who washed the deceased, which is not really our funeral rites. So that is not a real risk for us, especially if you know someone died of Ebola virus.

Speculating, what do you think happened with the two nurses?

It's a very interesting question. Since we know how to avoid Ebola virus infection, my assumption &mdash but it's really just an assumption &mdash is that they did not wear the correct protective gear or, most likely, they were not trained to wear the protective gear correctly. Because you have to make sure that you protect every little bit of your skin, that's so important. We talked about these droplets &mdash if tiny little parts of your skin are not covered, and the patient is bleeding, and you get these droplets somewhere on your skin and then you have a tiny, tiny little scratch --

That maybe you can't even see &mdash

Exactly. And we all have little scratches, or your eyes are not properly protected. Even a little bit of unprotected skin &mdash because of these little lesions we have in our skin &mdash is enough to get infected. And it’s also important to think about how you take off your protective gear, because if you’re covered in the bodily fluids of the patient and then you have to take it off, how do you do that without touching your skin at one point?

So we are in a very fortunate position in the Biosafety Level 4 labs because we have chemical showers &mdash and this is exactly why we have the chemical showers, to make sure that every part of us is somehow wetted with disinfectant, that we have contact with disinfectant everywhere. In the field, it’s very difficult to do that because you obviously don’t have chemical showers. Taking off the protective gear is something that needs a lot of training and very importantly, it needs a buddy system, you need somebody to help you to take off your protective gear. I don't know if that happened in Dallas but that's something that's very, very important. That is really the most dangerous part of it: even if you wear this protective gear, at one point you have to take it off, and how do you do that without touching somewhere on your skin?

In some ways, Ebola transmission seems reminiscent of HIV. Could you please compare the two?

Comparing Ebola to HIV is like comparing a a bulldozer to a high-end intelligent robot. Because Ebola is not at all adapted to us, so it just infects us, it kills us pretty quickly or at least causes severe disease, and then when we are done, the virus is done as well because if the host is dead, the virus is dead as well. Ebola virus causes what we call an acute infection: It lasts about two weeks and then it’s over one way or the other.

HIV is completely different. HIV manages to get its little tiny genome into our genome in the cells, and some of these cells survive forever, and that's the big issue with HIV. It becomes part of our own genomic equipment and so if these cells, which carry these little fragments, little HIV genomes, if they get activated, it really is not important how, then HIV starts to replicate its own genome and the infection starts again. That's what we call a persistent infection, which is much, much harder to fight. With the Ebola virus, my guess is it’s much simpler to fight the infection.

And in terms of transmission?

I already mentioned that Ebola virus causes a systemic infection, so the entire body is affected by the infection. HIV is much more picky about the cells it would like to infect it only infects a special subset of our immune cells &mdash T cells &mdash and it stays in these cells forever until the cells die, it's there. And since it is only in this special subset of blood cells, it’s only transmitted by blood and fluids, but not by sputum, for example, not by feces, not by saliva. The highest risk with HIV is sexual intercourse &mdash it’s almost the only risk, and contact with blood, of course. And that makes it so different.

But nevertheless, because HIV lasts in our body forever once we are infected, that’s the reason why if you are infected with HIV and you don’t get treatment that helps you get the viral concentration down, then you theoretically can spread the virus as long as you live. And that is different from Ebola virus because Ebola is cleared after two weeks. You’re virus free and maybe even protected from a new Ebola virus infection. There’s a lot of speculation about that &mdash we don't know for sure if Ebola patients are protected going forward.

The news lately has been that in Dallas, people are coming off of quarantine after 21 days &mdash that's solid, that after 21 days you're clear?

We know for Ebola virus the longest incubation period --- the time from when you get infected to the time you show symptoms, that’s the incubation period &mdash we ever heard about is 21 days. So if you're healthy for 21 days, you do not have the infection.

And that's different from having the infection and clearing it?

Then you have to do tests with these patients &mdash you have to look at their blood and see if there’s still virus. Once you see there’s no virus in the blood &mdash and you should repeat that at least two or three times to make sure there’s really no virus anymore &mdash if this is the case then the patients are cleared and safe. With one exception &mdash semen. That is a little bit strange, but it is as it is &mdash it seems that Ebola virus can last in the body a little bit longer, because there are reports that it has been transmitted by sexual intercourse after seven weeks or so. But patients, if they know about that, they can easily take care of it.

Do we have any idea why that would be, biologically?

Sorry, no! it’s very weird, it was completely unexpected but it happened, unfortunately.

Was it a single case report? Or more?

I know about one report of a very similar virus &mdash Marburg virus &mdash so that was a very well-controlled outbreak in 1967 in Germany, in Marburg, and exactly that happened. And one of the patients who survived the infection then infected his wife, and that’s why we know about that. There have also been reports of detection of Ebola virus in semen almost three months after the infection.

As you’ve watched media coverage and public reaction, any other scientific corrections you've especially wanted to make, or additions to public understanding of how Ebola is transmitted?

I think we really should focus on the outbreak in Africa. To make it crystal clear, we do not have an Ebola virus outbreak in the U.S. We do have an Ebola virus outbreak in West Africa. We have to do all we can do to stop this outbreak for our own good because we do not want to have a similar situation as the Dallas patient.

I also want to make clear that this virus is not transmitted by the air, and this virus will not be transmitted by the air. In virology, we are not aware of a single virus which changed its transmission route so dramatically. I've asked a lot of my colleagues: Are you aware of any virus which changed its transmission route? Any virus which went from blood-borne or transmitted by bodily fluids to airborne? And nobody knew of any virus.

Ever. In 100 years of virology. I would be glad to learn if that happened but I talked to a number of people and nobody could tell me a single example of that. It’s nature, you never know, a scientist never says never, but it’s very, very, very, very, very unlikely.

And I also want to mention, because we have cases not only here in the U.S. but I also heard about incidents in Europe &mdash that there was somebody sitting on the train, throwing up, and people surrounded this person &mdash a black person, which gives it some racist element too &mdash and completely freaked out and called 911, 'It’s Ebola, it’s Ebola!' And that won’t happen because Ebola virus patients are really sick, and that’s also something you should keep in mind. They do not walk around happily and all of a sudden they start to throw up, that is not the case. It's a deadly disease, and deadly means deadly, so you are ill and you won’t be able to walk around and infect people so easily.

You can’t really get out of bed by the time your fluids would be contagious?

Are there people who have been basically immune to Ebola virus?

That’s a very interesting question. There’s a very nice study by a French and African group, published in 2000, in which they identified what they called asymptomatic Ebola virus patients. There were people who had very close contact to Ebola virus patients but they did not become ill. They looked more closely at these people and they found that they had a very effective and well-regulated immune response to Ebola virus infection. They developed antibodies and they did not show any signs of infection. Obviously they were infected because they developed antibodies, but they were able to clear the infection.

So there are people like that.

Yes, but we don't know why that is the case. One possibility could be that there are genetic differences, of course. Another possibility could be that they were infected with only very very tiny little amounts of virus and the immune system was able to clear the infection before the concentration goes up like crazy. But we don't know the mechanism, not at all. That’s something that's very important to learn: Why do some people get infected but not develop the disease?

Most media coverage says clearly that Ebola is not airborne, but there was one piece in the Los Angeles Times with the headline, "Some Ebola experts worry virus may spread more easily than assumed." It referred to a monkey study in which monkeys that caught Ebola from each other were in close quarters and raised the question of whether it might be airborne.

If it’s the paper I think it is, there were no controlled conditions. It's not really clear how the virus was transmitted. That's scary. But we don't know how that happened.

There is another study that was published more recently, with Ebola virus Zaire, by Gary Kobinger in Winnipeg: His team infected pigs with Ebola virus Zaire and then monkeys in the same room as the pigs got infected. They obviously transmitted the virus but pigs are not the most clean and neat animals and they were in the same room.

What is really important is then they did exactly the same study with monkeys only: They infected monkeys with Ebola virus and they had another set of monkeys in the same room in another cage. In this case, the monkeys were not infected with the Ebola virus. So it was pig to monkey but not monkey to monkey, with Ebola virus Zaire.

I feel so much better.

You should get your flu vaccine, that’s much more important. That’s my last message to everybody: Please get your flu vaccine.

Readers, lingering questions?

Editor, CommonHealth
Carey Goldberg is the editor of WBUR's CommonHealth section.

First outbreak

The first recorded outbreak of Ebola was in 1976 in Zaire, according to the CDC. There were 380 cases that resulted in 280 deaths—a mortality rate of 88 percent.

That same year, an outbreak in Sudan killed 151 people among 284 reported cases.

Nearly 30 other outbreaks of Ebola have occurred since then, with the latest before this most recent instance in Uganda between 2012 and 2013.

Most outbreaks have been in Africa, with some limited cases during the last two decades reported in England, the Philippines, Russia and Italy.

Ebola was introduced in the U.S. when it was found in quarantined monkeys imported from the Philippines in 1989, 1990 and 1996.

But no human infections were discovered at that time.

Recently in the U.S., two American aid workers were diagnosed with Ebola in Liberia and treated in Atlanta.


Our findings show that in a cohort of 220 male EVD survivors from Sierra Leone, 75% of men were still semen positive for EBOV RNA 6 months after being discharged following acute EVD, and 50% at 204 days. At 1 year, less than 10% of study participants overall, but 20% of men aged >25 years who had had severe acute disease, had detectable EBOV RNA in semen. Longer persistence was significantly associated with increased age and severe acute EVD. The EBOV RNA positive rate in semen was considerably higher over time than what has previously been described. Earlier estimates of persistence rates among survivors based on longitudinal observations and modeling show lower estimates of EBOV RNA persistence rates. One study found persistence of 50% at 3.8 months [11] as compared to 50% remaining positive at close to 7 months in our cohort. Modeled estimates from the Postebogui cohort in Guinea, involving 27 men who tested positive in semen at least once, suggested a median duration of 45 days. In a later estimate by Keita et al. [11], the same population was estimated to have a 13%–60% probability of persistence at 6 months, but the probability was highly dependent on variations between different RT-PCR methods involved [11,25,26]. These studies provide important insights into findings from individual cases, followed up with different and sometimes long intervals. Our study involves a larger sample and does not rely on modeling outside of the survival analysis to estimate the population rates. Our finding of a 75% probability of persistence at 6 months hence represents an empirical longitudinal cohort analysis including regular, frequent follow-up and a large sample, which can explain the significant differences to earlier estimates.

The maximum duration of EBOV RNA positivity observed, 696 days, confirms published findings on EBOV RNA presence in semen from analyses of cross-sectional sample composition or case reports of maximum duration of EBOV RNA detection, including the baseline analyses of this study [9,12,13,27–29]. The higher than expected persistence over time we find in this large cohort of survivors, with 75% of men having EBOV RNA present at 6 months, sheds light on hypotheses raised by these studies, by here adding analyses of persistence rates over time from a representative male survivor sample.

We identified low adherence to initial safe sex counseling among 30% of the participants. In combination with our findings of higher than expected rates of EBOV RNA persistence in semen over time, the risk of residual sexual transmission is present. These results represent critical information to inform Ebola epidemic preparedness and response. The impact of a single case of sexually transmitted EBOV infection can be devastating, to both an individual and to public health, as evidenced by the case of sexual transmission 470 days after ETU discharge reported from Guinea [7]. Inconsistent condom use and limited compliance with the initial ETU recommendation of abstinence are identified challenges that merit immediate action to understand barriers to and facilitators of sustained risk reduction.

Our results further highlight the urgent need to ensure efforts to organize a national response providing semen testing, safe sex counseling, and free access to condoms, as a priority from the start of an outbreak. The here included results will inform forthcoming WHO updated guidelines on semen testing and will contribute to raising awareness of semen program testing needs in the context of the ongoing outbreak in DRC. Most semen testing needs would occur during the first year following ETU discharge, with half of the survivors expected to remain qRT-PCR positive up until close to 7 months. Based on our results, early risk identification and targeted counseling on long-term persistence risks among survivors, especially among those >25 years and with higher quantities of EBOV RNA in blood during acute disease, could be part of efforts to motivate safe sex and retain survivors in the testing program. These efforts will also need to be sustained, together with vigilance and responsiveness in the aftermath of the acute epidemic phase. The risk of new clusters of EVD igniting through sexual transmission demands a thorough and complex epidemic response over time, where a sustainable semen testing program is a crucial component.

Participants in our study who were older and those who had severe acute disease, defined as acute blood Ct value < 27, and those with diarrhea during acute EVD had a significantly higher probability of having persistent EBOV RNA in semen over time. Twenty percent of men with severe disease and >25 years had detectable EBOV RNA in semen at 1 year. Overall, younger age seemed to reduce the time to semen EBOV RNA clearance by dose–response pattern. This confirms hypotheses raised from other studies of survivors relating to men >40 years we show how the risk increase of longer persistence starts at an earlier age than earlier anticipated [9,12]. Several mechanisms, such as immune response to acute viremia, natural aging of the immune system, or inherent co-morbidity, may explain these associations.

The sociodemographic links to persistence merit further in-depth bio-behavioral research.

We found an unexpectedly low frequency of co-morbidity associated with acute EVD, which may be related to higher EVD case fatality rates in patients with additional diagnoses. Similar to other reports on Ebola survivors, the men in our study reported a high frequency (>60%) of post-EVD sequelae including symptoms of sexual fatigue [27]. These results highlight that survivors need continued care efforts, also addressing sexual health.

In this study we opted to use 2 consecutive negative qRT-PCR results, collected 2 weeks apart, as the definition of negativity, but keeping the “time of event” to the first test and applying interval censoring as needed, to accurately reflect time to event. For semen positive participants found positive at baseline, we assumed continuous positivity from ETU discharge until the first test at baseline.

ETU discharge date per certificate was used as the starting point for semen positivity. This date is a proxy for when viremia waned and will likely have underestimated persistence time. Acute Ct values in our study were not available for all participants, were taken at different points in time during acute disease, and were analyzed by different laboratories, which may have diluted the associations observed. The lowest available acute Ct value was consequently retrieved, to mitigate misclassification.

It should also be noted in all interpretations that the qRT-PCR detection of EBOV RNA does not distinguish between viable virus and RNA fragments. In an analysis by Whitmer et al. [20], including positive semen specimens from study participants in this cohort as well as from survivors in the US, it was shown that active EBOV replication occurred, and they concluded that “EBOV persistence within EVD survivors may act as a viral reservoir,” supporting the relevance of a positive qRT-PCR finding. [20].

Our study applied purposive sampling to recruit participants. The comparison of study participants with registered male survivors 18 years or above in Sierra Leone indicated differences across comparable demographic indicators of marriage and unemployment. These differences could reflect selection bias, influencing the generalizability of the results, but these traits were adjusted for as covariates in the multivariate analysis of associations with the outcome.

Recall bias may influence validity, specifically in the questions about the acute disease episode and sexual behavior. This and social desirability in answering may have lowered estimates of risky sexual behavior.


Our findings showed probabilities of semen persistence of EBOV RNA to be 75% at 6 months after ETU discharge, with persistence of 50% at 204 days and less than 10% at 1 year after ETU discharge. Persistence however remained at more than 20% at 1 year among participants >25 years with higher quantities of EBOV RNA in blood during acute disease. Uptake of safer sex recommendations 3 months after ETU discharge was low among a third of survivors. The study population was largely representative of the male EVD survivor population in Sierra Leon, apart from noted differences in marriage status and employment. These variables were adjusted for in the multivariate analysis, and we conclude that our results can be generalized to the wider male survivor population in Sierra Leone, and can also inform management and response to survivors’ needs following EVD in other contexts.

Our results highlight the immediate needs of planning for increased vigilance and efforts to support male survivors with safe sex counseling, including free provision of condoms at discharge, together with implementation of a semen testing program, as part of epidemic preparedness and primary and sustained epidemic response. Evidence exists showing sexual transmission chains after recovery however, more research is needed to better understand the contribution of sexual transmission at different points in an epidemic. Emerging EVD cases in the aftermath of an epidemic, as was the case in DRC, also merit in-depth analysis to understand the role of EBOV RNA semen persistence in survivors [30].


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