How long can it hide? NIAID

The Ebola virus can persist in a man’s semen for much longer than we thought. A man in Guinea who survived Ebola in 2014 is now known to have carried it for at least 531 days. Earlier this year, he transmitted the virus sexually, causing it to spread to at least 10 people, and killing 8 of them.

Ebola virus was known to persist in the testes of survivors, but until now the longest it had been detected surviving in this way was 284 days after a man’s recovery. The latest sexual transmission of the virus recorded had been 179 days after recovery.

If these long-lasting cases turn out to be more than just rare occurrences, Ebola has the potential to flare up again in the region of the 2014 epidemic for much longer than epidemiologists have been predicting.

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Guinea resurgence

The 2014 epidemic mainly affected Liberia, Sierra Leone and Guinea, and by May 2016 the World Health Organization had counted more than 28,000 cases of infection, and more than 11,000 deaths.

By the end of 2015, the WHO had declared that all known transmission chains in Guinea had ended, but in March this year, doctors in the town of N’Zérékoré reported that there had been three deaths that looked suspiciously like Ebola.

N’Zérékoré is in the forested region of Guinea where the 2014 epidemic first started, and health officials feared that the virus had crossed over from bats to humans again. But when they analysed the virus, they found it was very similar to the virus seen in a man in this area back in November 2014.

Tracing contacts through the area, epidemiologists found that the resurgence of the virus had in fact been sparked by this same man. Following medical advice, he had abstained from sex for 8 months after recovering from Ebola, but it now seems that this is not long enough.

Vanishing trick

In January, 470 days after he initially fell ill, this man had sex with the woman who became the first known case in this year’s outbreak. She then spread the virus to nine more people, one of whom carried it to Liberia.

The outbreak now seems to have been contained. But the fact that the Ebola virus can persist in semen for more than 500 days could mean other resurgences are likely.

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What this means for the risk of Ebola re-emerging depends on how the virus does this vanishing trick, and how often, says Andrew Rambaut at the University of Edinburgh, a co-author of the report of this case. The trick seems rare – there have only been a handful of known cases of sexual transmission of Ebola by survivors so far.

Rambaut is optimistic. The virus might not be transmissible the entire time that it is lurking – at some points, it may completely shut down.

“The more time that passes with no further flare-ups, the more likely it is that this case was exceptional,” says Rambaut.

On the other hand, as time passes, doctors may be becoming less likely to recognise when a case of fever is Ebola, raising the risk that the virus could be spread to more people.

Journal reference: Clinical Infectious Diseases, DOI: 10.1093/cid/ciw601