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NEJM Studies Explore Ebola Virus Persistence in Sperm, Confirm One Sexual Transmission Case

NEW YORK (GenomeWeb) – Studies by two independent research teams are supporting the notion that Ebola virus infection can be transmitted sexually through the semen of individuals who have recovered from the disease.

For the first of these studies, researchers from Sierra Leone, the US Centers for Disease Control and Prevention, the World Health Organization, and the Karolinska Institute used a quantitative RT-PCR assay to test semen samples from 93 Ebola virus disease survivors. Nearly half of the samples tested positive for the hemorrhagic fever-causing virus, including 11 semen samples from men who provided samples some seven to nine months after the onset of Ebola virus symptoms.

In general, their results suggest that the proportion of men with Ebola virus-positive semen samples dips with increasing time after disease onset, peaking in samples taken within the first few months after infection.

"Because semen-testing programs are not yet universally available, outreach activities are needed to provide education regarding recommendations and risk to survivor communities and sexual partners of survivors in a way that does not further stigmatize the community of survivors of [Ebola virus disease]," authors of the study wrote.

As part of a pilot study in Sierra Leone focused on determining how long Ebola virus sticks around in body fluids from infection survivors, the team enrolled 100 men between the ages of 18 and 58 years who had survived Ebola.

Samples from some men were collected just a few months after disease onset, while other samples came from men who were nearly a year out from disease onset.

All told, the researchers successfully analyzed semen samples from 93 of the men using RT-PCR assays that targeted NP and VP40 regions of the Ebola virus as well as the human beta2-microglobulin gene. Almost half of the men — 49 percent — had Ebola-positive semen samples by RT-PCR.

Nine men provided samples within two or three months of Ebola virus disease onset. Without exception, those samples tested positive for Ebola virus.

The team saw lower rates of Ebola-positive samples in the 40 individuals tested four to six months after their first Ebola symptoms. There, 26 individuals had positive semen tests for Ebola.

At seven to nine months out from disease onset, 11 of 43 men had Ebola virus-positive semen, while results were indeterminate for a sample collected from a man at the 10-month point.

The authors of that study emphasized that transmission by survivors seems to be quite rare, though "[w]e do not yet have data on the extent to which positivity on RT-PCR is associated with virus infectivity."

In another NEJM paper, a US Army Medical Research Institute for Infectious Diseases-led team confirmed one case of sexual transmission through whole-genome sequencing on semen samples from a male Ebola virus disease survivor and several blood samples, including samples from a woman who became infected and died from Ebola virus disease in Liberia in March.

The case was unusual, since the woman had no known contact with acutely infected individuals, the researchers explained. But the woman had had unprotected sex with a man who survived Ebola and had been released from the hospital five months earlier.

When the team did Illumina MiSeq sequencing on a blood sample from the deceased woman, they found that it contained a form of Ebola virus that was nearly identical to the Ebola virus RNA in the survivor's semen, which was sequenced with the help of an Illumina TruSeq kit with custom capture probes after her death.

The sequence was similar to that detected in the man's brother during an earlier infection, but was distinct from those turning up in cases appearing in the region between late-December and mid-February.

Semen samples provided by the survivor at the end of April and early May both tested negative for Ebola virus by RT-PCR.

In an accompanying editorial article in NEJM, Armand Sprecher from Doctors Without Borders in Brussels said findings from the study suggest longer surveillance periods may be needed before Ebola virus outbreaks can be considered over. He also encouraged careful consideration when coming up with ways to deter new infections without adding to the stigma that already surrounds survivors in some regions.