A new study of male Ebola survivors has revealed the virus lives on in semen and can be transmitted to sexual partners, months after the sufferer appears to have staged a full recovery.

The report published in the New England Journal of Medicine found two-thirds of men had Ebola in their semen after six months, and a quarter after nine months.

The study included 93 male Ebola survivors over the age of 18 from Freetown who gave semen samples for testing.

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The men enrolled in the study two to 10 months after their illness began.

All of the men who were tested in the first three months after becoming ill were positive for Ebola virus. 

“Why some study participants had cleared the fragments of Ebola virus from semen earlier than others remains unclear,” the researchers said about their results.

A separate study found that Ebola can be sexually transmitted by a survivor six months after symptoms began.

A lab worker in protective Ebola gear. Photo: AAP

The massive outbreak in Africa that emerged in 2013 has killed 11,000 people, but this time there were many more survivors than previous outbreaks.

“We have very little understanding of the long-term health consequences of having survived Ebola infections,” said Ilhem Messaoudi, an associate professor of biomedical sciences at the University of California.

“The reason for that is because most outbreaks up until 2014 have been smaller in scale and located primarily in remote villages and the mortality rate was in the 90 per cent or upwards of 90 per cent.”

Associate Professor Messaoudi said the research will revolutionise care for Ebola survivors, since people who survive the infection are facing challenges that doctors did not know about previously.

This includes the discovery that the virus can live on in the semen of male survivors and can also be transmitted to their sexual partners.

The researchers also found that the Ebola virus can hide in the eye, in the ocular fluid of the ocular chamber.

“It’s opening a whole new can of worms, so to speak, in terms of, well, is it a viable virus? Is it going to be transmitted? Can it cause disease in new patients?” Associate Professor Messaoudi said.

“And this particular study clearly demonstrates that Ebola can be transmitted via sexual contact, which is a whole new mode of transmission that was completely underappreciated until very recently.”

‘Potential source of new infections’

Jonathan Ball, a molecular virology professor at Britain’s Nottingham University, said the findings were worrying.

“This confirms that Ebola virus can persist in the genital tract for a considerable length of time, months after the virus has disappeared from the blood, and worryingly shows that this long-lived reservoir is a potential source of new infections,” Professor Ball said.

Clinical trials of a vaccine in Guinea show a 100 per cent success rate.

It said further tests of the samples were being conducted by the US Centres for Disease Control and Prevention “to determine if the virus is live and potentially infectious”.

Jeremy Farrar, an infectious diseases expert and director of Britain’s Wellcome Trust global health charity, said the findings highlighted “just how much we still don’t understand about the Ebola virus, infection and recovery”.

“It also reminds us that the Ebola epidemic could be far from over,” he said.

“With more than 17,000 Ebola survivors, it’s possible that further cases of delayed transmission and late complications will occur.”

The World Health Organisation’s (WHO) advice is that all male survivors should be tested three months after the onset of symptoms and then monthly until they know they have no risk of passing on the virus.

“Until a male Ebola survivor’s semen has twice tested negative, he should abstain from all types of sex or use condoms when engaging in sexual activity,” the WHO said.

“Hands should be washed after any physical contact with semen.”

-ABC, with agencies