The WHO declared Sierra Leone free of Ebola virus transmission in the human population last month (7 November), with the country now in a heightened 90-day surveillance.
But the findings of the study published in the New England Journal of Medicine on 14 October indicates declining virus persistence in semen of survivors with time from the onset of Ebola virus disease (EVD).
“Declining persistence means that even if the virus exists, there is evidence that they don’t multiply.”
Jackson Amone, Uganda’s Ministry of Health
The study, jointly commissioned by the World Health Organization (WHO), the Government of Sierra Leone and the US-based Centers for Disease Control and Prevention (CDC), started in mid-May this year with 100 male Ebola virus disease (EVD) survivors from the Western Area District of Sierra Leone.
“It is an observational cohort study, and we included survivors at different points in time after they had been discharged from the Ebola Treatment Unit. We ask them to provide semen at the first visit and they come back two weeks later,” explains Nathalie Broutet, a co-author of the study and an epidemiologist with the WHO's Department of Reproductive Health and Research in Geneva, Switzerland.
Broutet adds: “If they are positive, then they continue to come back. If they are negative, they come back another two weeks after. If they continue to be negative, they are finished with the study.”
About 20 participants yet to register negative results in are still being observed, says Broutet, adding that the study will last as long as they continue to have positive results.
According to the study, 49 per cent of 93 participants who provided semen had positive results. All nine survivors whose semen samples were tested two to three months after EVD onset were positive, compared to 65 per cent of 40 survivors tested four to six months and 26 per cent of 43 participants tested seven to nine months after its onset.
The WHO Ebola situation report published last week (2 December) indicates no confirmed cases in the week to 29 November. During this outbreak, a total of 28,601confirmed, probable and suspected EVD cases were reported in Guinea, Liberia and Sierra Leone, resulting in 11,300 deaths, says the report.
The researchers say while sexual transmission is deemed rare, many EVD survivors are sexually active and there are fears that this can trigger new outbreaks in the region weeks after all known transmission chains have stopped.
Jackson Amone, assistant commissioner for integrated curative services at Uganda’s Ministry of Health, says: “Declining persistence means that even if the virus exists, there is evidence that they don’t multiply.” The investigators are gaining more information about Ebola and they hope to clarify the determinants of virus persistence in survivors’ semen in the next phase.
Barbara Knust, a co-author of the study and an epidemiologist with the CDC, tells SciDev.Net: “We are looking at many possible factors, including, for example, the severity of illness, the relationship between the date of symptom onset and subsequent hospitalisation, and the course of treatment.”
The study will also be expanded to include analysis of vaginal secretions from 120 female EVD survivors in Sierra Leone, Broutet says.
This piece was produced by SciDev.Net’s Sub-Saharan Africa (English) desk.
References Gibrilla F. Deen and others Ebola RNA persistence in semen of Ebola virus disease survivors — preliminary report (New England Journal of Medicine, 14 October 2015)
 World Health Organization Ebola situation report (WHO, 2 December 2015)