Medical practice

Is Ebola an STI? Virus can survive in semen for up to nine months

"Survivors of Ebola can carry the virus in their sperm and transmit it sexually for up to nine months, a study has found," The Guardian reports.

It was previously thought the Ebola virus stayed in bodily fluids for just three months after the illness.

An obvious concern is that sexual spread of the virus could trigger another outbreak, such as the previous 2014/15 outbreak that killed thousands of people in Sierra Leone, Liberia and Guinea, leaving more than 16,000 survivors. 

The researchers found traces of Ebola virus RNA in semen samples from a group of Ebola survivors from Sierra Leone, who had been sick between two and 10 months earlier. 

The researchers say they don't know whether the traces of viral RNA detected in the men's semen came from intact viruses that could replicate and pass on the infection. They may be from fragments of virus that are no longer active.

However, a second study in the same journal found that a Liberian woman was very likely to have been infected by the Ebola virus through sex with an Ebola survivor, about six months after he was infected.

Together, the studies demonstrate that the possibility of further outbreaks of Ebola, caused by sexual transmission of the virus, cannot be dismissed.

These results, tentative as they are, do stress the usefulness of the simple, but effective, condom in helping to prevent the spread of a range of diseases.

Where did the story come from?

The first study was carried out by researchers from the Sierra Leone Ministry of Health and Sanitation; Sierra Leone Armed Forces; Sierra Leone Ministry of Social Welfare, Gender and Children’s Affairs; the Centers for Disease Control and Prevention (CDC); the World Health Organization (WHO); and the Karolinska Institute. 

It was funded by the WHO, CDC, Sierra Leone government and a Joint United Nations Program on HIV/AIDs. 

The second study was done by researchers from the US Army Medical Research Institute of Infectious Diseases; US National Institutes of Health; Liberian Ministry of Health and Social Welfare; Liberian Institute for Biomedical Research; CDC; WHO; Illumina; Naval Medical Research Unit; and the Foundation Merieux. 

It was funded by the Defense Threat Reduction Agency; Global Biosurveillance Technology Initiative; Global Emerging Infections Surveillance; Illumina; and the National Institutes for Health.

Both studies were published in the peer-reviewed journal The New England Journal of Medicine on an open-access basis, so they can be read for free online. The first is on the persistence of Ebola RNA in semen and the second is a case report showing that the virus can be spread through sexual intercourse.

BBC News and The Guardian both covered the story, in the most part, accurately. However, The Guardian reported that "survivors carry virus in their sperm", although the virus RNA is actually found in semen – the fluid that sperm live in – rather than in the sperm themselves.

What kind of research was this?

The first study was a cross-sectional cohort study using a convenience sample of volunteers. This type of study can only give us limited information, because we don't know what happens to the people in the study over time, or whether the volunteers represent the wider population.

The second study is a case report on an investigation of possible sexual transmission of Ebola virus between two people, using genomic analysis (a type of DNA analysis).

What did the research involve?

In the first study, researchers recruited 100 men who had been certified as having recovered from Ebola (which would include negative blood tests for Ebola). Each man filled out a questionnaire about his illness, and was asked to give at least one sample of semen. 

The researchers looked to see how long ago the men had been sick, when they recovered, and whether they had traces of Ebola RNA in their semen.

The tests look for evidence of genetic sequences found in the Ebola virus. However, the tests cannot tell whether these sequences are from whole, live virus, which might be infectious, or from broken-down fragments of virus, which might be harmless. Also, because the study is a snapshot in time, it cannot tell us how long signs of Ebola virus might persist in the semen. 

The study is ongoing, so longer-term data will be published in due course. The researchers also did an analysis to see how much virus there was likely to be in the semen – known as the viral load.

The second study analysed the Ebola virus RNA found in samples of blood from a woman who had died of Ebola, and blood and semen samples from her partner, an Ebola survivor, to see how likely it was that the woman had been infected by the man during unprotected sex. 

The researchers compared their results with samples from other parts of Liberia, and other contacts of the pair, to see if it was likely the woman could have been infected by another route.

What were the basic results?

The researchers had usable semen samples from 93 men in the first study. In total, half showed positive results for Ebola RNA. The samples taken from nine men who had been ill recently (within two to three months) all tested positive.

For those who had been ill four to six months earlier, 26 out of 40 (65%) were positive. For those who had been ill seven to nine months earlier, 11 out of 43 (26%) were positive, and the one man who had been ill 10 months earlier had inconclusive results. The tests for estimating viral load suggested that this became lower over time.

The results from the second study showed that the RNA of the Ebola virus found in samples from the man and woman were very similar, and much more similar than the RNA found in samples from other survivors in Liberia.

How did the researchers interpret the results?

The researchers were cautious about their results. Of the first study, they said: "the public health implications are still uncertain", because they cannot be sure whether the Ebola RNA detected in the semen was actually infectious.

However, they say they have demonstrated "the potential for transmission … even months after the outbreak has ended". They call for programmes to test and counsel survivors of Ebola about their individual risk and the best ways to avoid infecting partners.

In the second study, the researchers say "at least one case of Ebola virus disease in the ongoing Liberian outbreak probably resulted from sexual transmission through unprotected vaginal intercourse". 


Taken together, these studies suggest that traces of Ebola virus may remain in bodily fluids of survivors many months after people have recovered. In some cases, these traces may lead to the infection being passed on, as in the case of the Liberian man and woman in the second study. However, we don't know whether that is possible for all, or even most, people who have survived Ebola.

There have been few reports of Ebola virus being passed on through sexual contact. Given the large numbers of people who have had Ebola, and the small number of cases in recent months, it may be that Ebola is not easily transmissible by this route. 

However, there is not enough information available to speculate about this. We need much more data to know how long the virus can persist in bodily fluids, and whether it remains infectious.

In the meantime, doctors have called for the previous advice for Ebola survivors to abstain from sex or use condoms for three months to be changed. Ideally, survivors should be tested regularly, given information about their own risk, and advised to take precautions to protect their sexual partners accordingly.

The scale of the Ebola outbreak of 2014/15 has made it more important to find out about sexual transmission, because there are so many survivors now living back in their communities. 

Previous outbreaks tended to be smaller and more isolated, meaning there was less chance of transmission after the initial outbreak had been controlled.

Dr Jeremy Farrar, director of the Wellcome Trust, said the studies showed "the Ebola epidemic could be far from over". 

Using a barrier method of contraception, such as a condom during sex (including anal and oral), remains the most effective method of reducing your risk of contracting a sexually transmitted infection (STI)

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