Volume 25, Number 2—February 2019
Ebola Virus Infection Associated with Transmission from Survivors
The 2014–2016 outbreak of Ebola virus disease (EVD) in West Africa was the largest since the discovery of the Ebola virus (EBOV) in 1976 (1). More than 28,000 cases and 11,000 deaths were reported from the 3 most affected countries (Guinea, Liberia, and Sierra Leone) (2). An unprecedented number of persons survived; >4,500 of the estimated total of >10,000 survivors have been registered in the 3 countries (3).
EVD survivors often have substantial long-term medical sequelae (4), and viable EBOV can persist in immunologically protected body sites, such as the male gonads and the chambers of the eye (5,6). Viral persistence in body fluids, such as semen, creates the potential for transmission and initiation of new chains of transmission weeks or months after continuous community transmission has ended (7). On January 14, 2016, the World Health Organization (WHO) declared that human-to-human transmission had been stopped in West Africa. However, WHO and its partners indicated that the 3 affected countries remained at high risk for additional EVD outbreaks because of virus persistence in survivors and emphasized the need for strong surveillance and response systems (8). A new EVD case was confirmed in Sierra Leone the following day (9), and another outbreak comprising cases in both Guinea and Liberia was recognized in March 2016 (2,10).
Infectious virus has been isolated from semen of Ebola survivors 82 days after symptom onset (11), and EBOV RNA has been detected by reverse transcription PCR (RT-PCR) in semen 531 days after symptom onset (10). Other body fluids, such as vaginal fluids, breast milk, urine, feces, sweat, and saliva, also have been shown to be RT-PCR–positive for short periods after recovery of the patient (11). Some evidence indicates that transmission could occur through breast milk (12), but confirmed transmission from viral persistence in the other body fluids has not been described (13). Before the West Africa EVD outbreak, 1 case of Marburg disease (14) and 1 possible case of EVD (15) attributed to sexual transmission had been reported. From the EVD outbreak in West Africa, several incidents of possible sexual transmission of EBOV from EVD survivors have been described in detail (10,16–19), as have viral persistence–derived transmission of EBOV (VPDTe) events for which the mode of transmission was unknown (12,20,21,22).
We describe a series of EBOV transmission events with evidence of transmission related to viral persistence in EVD survivors. Our findings are relevant for response planning, especially related to surveillance and response capacity, and for the development of policies and guidelines regarding survivor counselling, care, and management.
We defined VPDTe as the person-to-person transmission of EBOV from an EVD survivor (source) to another person (recipient) that occurred >21 days after the source case recovered from acute infection. The WHO definition of recovery is >3 days without any fever or symptom and negative blood RT-PCR for EBOV; however, this documentation was not available for all patients (23). The 21-day period reflects the upper limit of the incubation period for EVD; incorporating this period into the definition reduces the likelihood that the recipient was not infected during the period of acute infection of the source. The recipient is the person who becomes infected as a result of VPDTe. A recipient might or might not be the first person (index person) detected in a newly identified cluster of EVD cases (and in some situations, clearly identifying the recipient might not be possible). We defined confirmed, probable, and suspected cases of EVD and EVD survivors in accordance with WHO definitions (24).
We focused our identification of VPDTe events on the period after control of the most intense periods of transmission in the affected countries and retrieved information about possible VPDTe events identified after February 19, 2015 (after the initial interruption of ongoing transmission in Liberia). During this time, low case counts facilitated recognition and subsequent in-depth case investigation of new EVD cases that were not clearly related to continuous disease transmission in the community and might have resulted from exposure to a survivor with viral persistence. In September 2015, we began to maintain a formal list of suspected VPDTe events identified by staff involved in epidemiologic investigations in the 3 countries. The data were entered retrospectively or prospectively into the formal list.
For all events, the field teams collected information at the time the case or cluster of cases was detected. We extracted data from available databases, WHO Situation Reports, region- and country-specific situation reports, email correspondences to the WHO Ebola Response Information Management team, case investigation reports, transmission chains (including the number of additional cases and generations in the cluster), and genetic sequencing results. We captured demographic data; dates of symptom onset, diagnosis, discharge, and death; laboratory results; epidemiologic investigation details; sequencing data; data on how the cases were initially recognized; information on encounters with healthcare providers; details of outbreak control efforts; and information about the secondary cases.
We developed criteria to determine which transmission events qualified as resulting from viral persistence (Table 1). We also developed criteria for source of transmission (Table 2), mode of transmission, and the strength of the evidence for transmission (strong, moderate, or weak) (Table 3). If the investigation identified >1 possible mode of transmission, these criteria for strength of evidence and evaluation of the route of transmission were not tabulated. Two investigators (S.D., B.J.M.) independently reviewed and classified each transmission event, and a third (S.S.S.) resolved differences.
The WHO Ethics Review Committee (ERC.0002736) approved this activity, and the Centers for Disease Control and Prevention classified it as a nonresearch program activity. The analysis of these surveillance data from the EVD epidemic was approved by representatives of the Ministry of Health in each of the 3 countries and was not considered to require additional ethics review. In accordance with the approved protocols, we have omitted information that would enable identification of specific persons.
We identified 13 transmission events that met criteria for VPDTe during the evaluation period (Appendix). We identified a recipient for 8 events; among these, 7 were female. Ages of all recipients ranged from 16 to 55 years. For the remaining 5 events, the recipient was not clearly identified, and the first person identified in the cluster might or might not have been the recipient. For these VPDTe events, we report details for the first person identified. Eight of the 13 events have previously been described separately in the context of outbreak investigations (10,12,16–22).
Description of VPDTe Events Not Previously Described Elsewhere
Postmortem testing determined the recipient in this event had EVD. No cases had occurred in the immediate area during the 7 weeks before the report of the index person. Although initial epidemiologic investigation suggested possible exposures through funeral attendance, viral sequencing suggested a link to an EVD cluster that had occurred in a nearby geographic area ≈7 weeks earlier. That cluster included 1 male survivor; he reported sexual contact with the recipient. A semen sample from the survivor tested positive for EBOV RNA by RT-PCR. Sexual contact was considered the likely route of transmission.
The recipient in this event died in the community the same day as symptom onset; EVD was confirmed by testing of a postmortem oral swab sample. Based on genetic sequencing, the virus from the recipient did not group with ongoing chains of transmission but did group with sequences from viruses identified earlier in the epidemic. Epidemiologic investigations showed the recipient had had sexual contact with a male EVD survivor 2 months after his discharge from an Ebola treatment unit and ≈1–3 weeks before she became symptomatic. Semen from the survivor was not tested, but EBOV RNA from a stored blood sample collected during the survivor’s initial illness showed genetic sequence that was similar to that of the recipient.
In this event, a young woman with symptoms of EVD sought care at a healthcare facility, and EVD was confirmed by RT-PCR. Epidemiologic investigation found no history of travel, funeral attendance, or bush meat consumption. There was no known ongoing transmission in the village or district. Sequences of viral RNA from the recipient clustered with isolates from cases that occurred in the same area 5–11 months earlier but differed substantially from available individual sequences from persons with contemporaneous confirmed EVD. The route of transmission is unknown.
In this event, a man had EVD confirmed based on a swab specimen collected after his death. Sequencing linked his virus to viruses from cases 5 months earlier in a different district. No specific epidemiologic links to recent or more remote cases were identified. The source and route of transmission are unknown.
This event involved EVD reported in a woman 2 days after her death and confirmed by testing of a postmortem oral swab sample. Her viral sequence did not match contemporary circulating strains of EBOV but did link to strains from ≈5–6 months earlier. Her husband spent time in both the community where she lived and in the capital city; he had experienced an illness compatible with EVD 5–6 months earlier but had not been tested. Two other persons had died recently in the family (a co-wife and the child of the co-wife), and a stillbirth occurred (to the niece of the recipient); no testing for EVD had been conducted in these situations. Transmission had not been recognized in the community before the recognition of this cluster of illness, and there was no known exposure to an ill person or funeral. The source and route of transmission are unknown. One possible explanation is that the husband was an EVD survivor and had transmitted EBOV through sexual or other contact to >1 members of the family; direct transmission also might have occurred from close contact.
Mode of Transmission and Strength of Evidence
For 4 events, we could not identify a single clear hypothesis for how transmission occurred. All 4 of these have been described in separate publications (12,16,21,22). Five events met our defined criteria for sexual transmission (Appendix Table). The evidence was strong for 4 events and moderate for 1 event. Among these 5 VPDTe events of suspected sexual transmission, we identified the survivor believed to be the source; all were male. The other 8 VPDTe transmission events for which the mode of transmission is unknown were considered to be due to survivor transmission because they were isolated cases and sequencing results linked them to previous transmission chains. The routes of transmission are unknown.
Detection and Response
In 10 VPDTe events, EBOV infection was diagnosed in the index person on the basis of a postmortem sample or because it was preceded by deaths that met the definition for probable EVD; ultimately, all but 1 of the initially recognized cases or recipients of VPDTe died. Eight recipients had reported encounters with health providers before being tested for and receiving a diagnosis of EVD. For 6 VPDTe events, cases occurred in addition to the first recognized case (range 1–12 cases; Appendix Table). Most clusters were limited to 0 or 1 additional generation of cases, but in 1 cluster, several additional generations occurred.
After detection of the index person, response activities such as isolation and management of the index patient and contact tracing with isolation of high-risk and symptomatic contacts were initiated for all events. Seven cases occurred after initial control of ongoing transmission in a specific country and required reactivation of some response resources. Searches for missing contacts were intense and continued until at least the end of the initial 21-day follow-up period. For some clusters, there were difficulties engaging with local communities, complicating contact tracing. For at least 8 events, Ebola vaccine was provided to contacts and to contacts of contacts under research protocols and emergency use licensure.
On March 29, 2016, WHO declared the end of the Public Health Emergency of International Concern regarding the EVD outbreak in West Africa (25). In the declaration, WHO emphasized that new EVD clusters would continue to occur because of reintroductions of EBOV from survivors. Our case series summarized 13 such events.
Most of the events we describe were initially recognized because they occurred in isolation, in areas that EBOV had not previously affected or well after community transmission had ended. Plausible explanations for such cases include recrudescence of prior EVD, reintroduction from a zoonotic reservoir, transmission resulting from unrecognized contact with a person with active EVD, or transmission related to viral persistence. Recrudescence might have played a role in event 11, but EVD was not confirmed in the mother of the index person at the time of her initial EVD-like illness, and there was no documentation that she was shedding EBOV in the period preceding illness in the index person (22). We do not believe any of the other events described here occurred because of EBOV recrudescence. Based on sequencing data, the cases we describe were genetically related to other cases that occurred as part of human-to-human transmission in the West Africa epidemic; no evidence exists to indicate these cases resulted from reintroduction from a zoonotic reservoir. Given the absence of additional recognized transmission events, we believe it highly unlikely that the cases we summarized were part of undetected transmission chains.
Routes of VPDTe are not fully understood. We found evidence of sexual transmission in at least 5 of the events; sexual transmission might have played a role in additional events, but we cannot exclude other modes of VPDTe. EBOV was found in the breast milk of a woman in 1 cluster; transmission through breast milk might have occurred in this event.
We are unable to quantify the risk for VPDTe over time. There have been a limited number of cases of recognized sexual transmission, even though >10,000 persons are estimated to have survived (3). The number of male survivors who have EBOV persisting in semen declines over time, reducing the likelihood of events caused by sexual transmission (26). Transmission because of viral persistence in body fluids other than semen might occur but probably less frequently (3,12,13).
WHO’s interim advice on the sexual transmission of EBOV is that male EVD survivors should continue to practice safer sex (i.e., correct and consistent condom use or abstinence) for at least 12 months after symptom onset or until their semen has twice tested negative (27). This case series highlights 2 events of VPDTe that occurred >1 year after recovery by the source case. This information, along with information about the duration of persistence of EBOV RNA in the semen of survivors and data showing that EBOV RNA can be detected intermittently (7,28), needs to be considered in the development of recommendations for EVD survivors. Furthermore, recommendations on semen testing and safer sex practices, including timely updates if recommendations are revised in light of new evidence, must be clearly communicated to EVD survivors and to the public.
Ideally, counselling and testing should be offered as part of a comprehensive package of care for survivors that recognizes the challenges faced by survivors, including health problems, mental health problems, rejection, and stigma (29–33). Furthermore, partners and family members of EVD survivors need to be counseled, and community education about VPDTe needs to be provided.
An important element of surveillance for EVD is that early recognition of isolated cases is difficult. Despite the context of a recently controlled enormous EVD epidemic, most of the VPDTe cases were recognized very late in illness or after death. This finding speaks to the nonspecificity of EVD symptoms; the high prevalence of other diseases with similar symptoms; and the limited resources for identifying the specific cause of disease in low-resource settings, such as West Africa. Wider availability of diagnostic testing, for example with rapid tests, may support more timely diagnosis than would otherwise have been possible.
One new case of EVD could potentially result in large numbers of secondary cases (34). Therefore, it is critical to sustain the capacity to respond rapidly, particularly after an EVD outbreak, including the capacity to conduct outbreak investigation and trace contacts; efficient collection, transport, and laboratory diagnosis of specimens; isolation and clinical management of cases; and as appropriate, vaccination of contacts and contacts of contacts.
The responses to the events we describe were generally robust, and transmission was in most instances cases limited to 1 generation. This observation reflects the control capacity generated in the context of the broad outbreak response, a result of enormous effort on behalf of the governments and ministries of health of the affected countries and immense mobilization of resources from the international community and international partners.
Identifying routes of EBOV transmission is not straightforward. Rigorous epidemiologic investigation and evaluation of viral RNA sequences can provide helpful information. Sequencing helped to confirm the link to an epidemiological source for several cases and for some cases suggested a link that was later confirmed epidemiologically. Given this contribution, we believe that sequencing can play a critical role in efforts to control infectious diseases. Still, for several situations that appeared to involve viral persistence, the route of transmission was unclear, and even when we identified a single likely route of transmission, we could not exclude the possibility that we missed alternate possible routes of transmission.
Our findings are subject to several additional limitations. Specifically, our list of described events is unlikely to include all events of VPDTe. Particularly at the height of the outbreak, distinguishing between direct transmission from active EVD cases and VPDTe was not possible, and we therefore concentrated on describing cases that occurred after control of the most intense periods of transmission in the affected countries. Another study identified 2 additional EVD clusters possibly resulting from VPDTe by using the signature of a reduced evolutionary rate (21). Further analysis of sequence data from cases in West Africa might identify additional events of possible VPDTe. In the future, expanded use of sequencing and semen testing could help identify additional events.
Taking these limitations into consideration, the number of events identified here most likely underestimates VPDTe in West Africa. Furthermore, the information and evidence for each event was collected on an ad hoc basis, depending on the characteristics of the particular event. Where available, we collected information about viral sequence using various methods, and we relied on the reports and interpretations of sequence data rather than an analysis of the primary data. In some instances, source case documents included conflicting information and the deaths of all but 1 recipients or index persons limited the epidemiologic investigations. As a result, information about some of the events might be incomplete; despite intense investigation, in some cases, critical questions remain about how transmission occurred.
Our report has several key implications. EVD cases and clusters might occur after initial control of an EVD outbreak. Although previously available science supported the possibility of viral persistence, the West Africa outbreak clearly illustrated the potential consequences of EBOV persistence in terms of program needs, stigmatization of survivors, and risk that transmission from a survivor with persistent virus will trigger a new cluster. With this new reality, it is critical that the responses to EVD clusters include sustained vigilance, maintenance of response capacity, and continued efforts to reduce the risks that survivors in whom EBOV persists will transmit infection.
Dr. Den Boon is an epidemiologist and health economist currently working as a freelance consultant. Her primary research interests include priority setting of health interventions and implementation research to improve access to medicines.
We thank the many field staff from Guinea, Liberia, and Sierra Leone involved in EVD case finding, treatment, and testing of patients; contact tracing; epidemiologic investigations; sequencing; data collection; and data entry, including all members of the Guinea National Ebola Response team; Boubacar Diallo, Luke Bawo, Mosoka Fallah, all members of the Liberia Ebola Incidence Management System; Roland Conteh, and all members of the Sierra Leone National Ebola Response Centre; as well as Pierre Formenty, Stéphane Hugonnet, Patrick Otim, Dhamari Naidoo, Philomena Raftery, Shalini Singaravelu, Lisa Thomas, Annika Wendland, Sina Zintmeyer, Mame A. Akyeampong, M. Balihe, Sarah D. Bennett, David Blackley, A. Christie, B. Dahl, Emily K. Dokubo, David L. Fitter, S. Hersey, Barbara Knust, Anthony S. Laney, Lise D. Martel, Dan W. Martin, Eric O.K. Mensah, E. Meyer, Maria Negron, Fatima Ravat, John T. Redd, Pierre Rollin, Kendra Stauffer, Brittany Sunshine, Emily Weston, Desmond Williams, Mary Claire Worrell, Jonathan S. Yoder, James Zingeser, and F.-W. Tremblay.
- Ebola haemorrhagic fever in Sudan, 1976. Report of a WHO/International Study Team. Bull World Health Organ. 1978;56:247–70.
- World Health Organization. Ebola situation report 30 March 2016 [cited 2016 Apr 11] http://apps.who.int/ebola/current-situation/ebola-situation-report-30-march-2016
- World Health Organization. Clinical care for survivors of Ebola virus disease. Interim guidance [cited 2016 Apr 11]. http://www.who.int/csr/resources/publications/ebola/guidance-survivors/en/
- Clark DV, Kibuuka H, Millard M, Wakabi S, Lukwago L, Taylor A, et al. Long-term sequelae after Ebola virus disease in Bundibugyo, Uganda: a retrospective cohort study. Lancet Infect Dis. 2015;15:905–12.
- Bausch DG, Towner JS, Dowell SF, Kaducu F, Lukwiya M, Sanchez A, et al. Assessment of the risk of Ebola virus transmission from bodily fluids and fomites. J Infect Dis. 2007;196(Suppl 2):S142–7.
- Varkey JB, Shantha JG, Crozier I, Kraft CS, Lyon GM, Mehta AK, et al. Persistence of Ebola virus in ocular fluid during convalescence. N Engl J Med. 2015;372:2423–7.
- Deen GF, Broutet N, Xu W, Knust B, Sesay FR, McDonald SLR, et al. Ebola RNA persistence in semen of Ebola virus disease survivors—final report. N Engl J Med. 2017;377:1428–37.
- World Health Organization. Latest Ebola outbreak over in Liberia; West Africa is at zero, but new flare-ups are likely to occur [cited 2016 Mar 1]. http://www.who.int/mediacentre/news/releases/2016/ebola-zero-liberia/en/
- World Health Organization. New Ebola case in Sierra Leone. WHO continues to stress risk of more flare-ups [cited 2016 Mar 1]. http://www.who.int/mediacentre/news/statements/2016/new-ebola-case/en/
- Diallo B, Sissoko D, Loman NJ, Bah HA, Bah H, Worrell MC, et al. Resurgence of Ebola virus disease in Guinea linked to a survivor with virus persistence in seminal fluid for more than 500 days. Clin Infect Dis. 2016;63:1353–6.
- Rodriguez LL, De Roo A, Guimard Y, Trappier SG, Sanchez A, Bressler D, et al. Persistence and genetic stability of Ebola virus during the outbreak in Kikwit, Democratic Republic of the Congo, 1995. J Infect Dis. 1999;179(Suppl 1):S170–6.
- Sissoko D, Keïta M, Diallo B, Aliabadi N, Fitter DL, Dahl BA, et al. Ebola virus persistence in breast milk after no reported illness: a likely source of virus infection from mother to child. Clin Infect Dis. 2017;64:513–6.
- Thorson A, Formenty P, Lofthouse C, Broutet N. Systematic review of the literature on viral persistence and sexual transmission from recovered Ebola survivors: evidence and recommendations. BMJ Open. 2016;6:e008859.
- Martini GA, Schmidt HA. [Spermatogenic transmission of the “Marburg virus”. (Causes of “Marburg simian disease”)] [in German]. Klin Wochenschr. 1968;46:398–400.
- Rowe AK, Bertolli J, Khan AS, Mukunu R, Muyembe-Tamfum JJ, Bressler D, et al. Clinical, virologic, and immunologic follow-up of convalescent Ebola hemorrhagic fever patients and their household contacts, Kikwit, Democratic Republic of the Congo. Commission de Lutte contre les Epidémies à Kikwit. J Infect Dis. 1999;179(Suppl 1):S28–35.
- Keita M, Duraffour S, Loman NJ, Rambaut A, Diallo B, Magassouba N, et al. Unusual ebola virus chain of transmission, Conakry, Guinea, 2014–2015. Emerg Infect Dis. 2016;22:2149–52.
- Christie A, Davies-Wayne GJ, Cordier-Lassalle T, Blackley DJ, Laney AS, Williams DE, et al.; Centers for Disease Control and Prevention (CDC). Possible sexual transmission of Ebola virus - Liberia, 2015. [Erratum in Morb Mortal Wkly Rep 2015;64:1180]. MMWR Morb Mortal Wkly Rep. 2015;64:479–81.
- Mate SE, Kugelman JR, Nyenswah TG, Ladner JT, Wiley MR, Cordier-Lassalle T, et al. Molecular evidence of sexual transmission of Ebola virus. N Engl J Med. 2015;373:2448–54.
- Arias A, Watson SJ, Asogun D, Tobin EA, Lu J, Phan MVT, et al. Rapid outbreak sequencing of Ebola virus in Sierra Leone identifies transmission chains linked to sporadic cases. Virus Evol. 2016;2:vew016.
- Alpren C, Sloan M, Boegler KA, Martin DW, Ervin E, Washburn F, et al.; Interagency Investigation Team. Notes from the field: Ebola virus disease cluster—northern Sierra Leone, January 2016. MMWR Morb Mortal Wkly Rep. 2016;65:681–2.
- Blackley DJ, Wiley MR, Ladner JT, Fallah M, Lo T, Gilbert ML, et al. Reduced evolutionary rate in reemerged Ebola virus transmission chains. Sci Adv. 2016;2:e1600378.
- Dokubo EK, Wendland A, Mate SE, Ladner JT, Hamblion EL, Raftery P, et al. Persistence of Ebola virus after the end of widespread transmission in Liberia: an outbreak report. Lancet Infect Dis. 2018;18:1015–24.
- World Health Organization. Clinical management of patients with viral haemorrhagic fever. A pocket guide for front-line health workers. Interim emergency guidance for country adaptation. February 2016 [cited 2016 Mar 1]. http://apps.who.int/iris/bitstream/handle/10665/205570/9789241549608_eng.pdf
- World Health Organization. Case definition recommendations for Ebola or Marburg virus diseases [cited 2016 Feb 16]. http://www.who.int/csr/resources/publications/ebola/case-definition/en/
- Statement WHO. Statement on the 9th meeting of the IHR Emergency Committee regarding the Ebola outbreak in West Africa [cited 2016 Apr 4]. http://www.who.int/mediacentre/news/statements/2016/end-of-ebola-pheic/en/
- Eggo RM, Watson CH, Camacho A, Kucharski AJ, Funk S, Edmunds WJ. Duration of Ebola virus RNA persistence in semen of survivors: population-level estimates and projections. Euro Surveill. 2015;20:30083.
- World Health Organization. Interim advice on the sexual transmission of the Ebola virus disease. January 2016 [cited 2016 Feb 8]. http://www.who.int/reproductivehealth/topics/rtis/ebola-virus-semen/en/
- Fischer WA, Brown J, Wohl DA, Loftis AJ, Tozay S, Reeves E, et al. Ebola virus ribonucleic acid detection in semen more than two years after resolution of acute Ebola virus infection. Open Forum Infect Dis. 2017;4:ofx155.
- Clark DV, Kibuuka H, Millard M, Wakabi S, Lukwago L, Taylor A, et al. Long-term sequelae after Ebola virus disease in Bundibugyo, Uganda: a retrospective cohort study. Lancet Infect Dis. 2015;15:905–12.
- Davtyan M, Brown B, Folayan MO. Addressing Ebola-related stigma: lessons learned from HIV/AIDS. Glob Health Action. 2014;7:26058.
- Reardon S. Ebola’s mental-health wounds linger in Africa. Nature. 2015;519:13–4.
- Yadav S, Rawal G. The current mental health status of Ebola survivors in Western Africa. J Clin Diagn Res. 2015;9:LA01–02.
- Sprecher A. Handle survivors with care. N Engl J Med. 2017;377:1480–2.
- Althaus CL. Ebola superspreading. Lancet Infect Dis. 2015;15:507–8.
Suggested citation for this article: Den Boon S, Marston BJ, Nyenswah TG, Jambai A, Barry M, Keita S, et al. Ebola virus infection associated with transmission from survivors. Emerg Infect Dis. 2019 Feb [date cited]. https://doi.org/10.3201/eid2502.181011
Original Publication Date: 11/30/2018
1These authors contributed equally to this article.