Nurse Who Had Ebola Re-hospitalized and Now Critically Ill

The journal also published details of an Ebola case in March in Liberia, where a male survivor spread Ebola to a woman via unprotected sex five months after he became infected.

Researchers had suspected this might happen, but this is the first proof. She said Ms Cafferkey had gone to a GP out-of-hours clinic at the Victoria Hospital in Glasgow on Monday night but the doctor who assessed her diagnosed a virus and sent her home.

Male Ebola survivors should be offered semen testing at three months after onset of disease, and then, for those who test positive, every month thereafter until their semen tests negative for virus twice by RT-PCR, with an interval of one week between tests.

Ninety three men over the age of 18 from Freetown, Sierra Leone, provided a semen sample that was tested to detect the presence of Ebola virus genetic material. Among the samples taken four to six months after an Ebola infection, 65 percent carried signs of the virus, and 26 percent of the samples taken at the seven- to nine-month mark also tested positive for the virus.

Dr. Francis Moses, a district medical officer in northern Sierra Leone, said it was hard convincing male Ebola survivors to use condoms or abstain from sex.

People with Ebola are believed to be most infectious when they are the sickest. More than 28,000 people were infected and more than 11,000 died.

"There are a lot of survivors in West Africa", Knust said. But it had been impossible to prove.

"Let's pray a daily Hail Mary again for nurse Pauline Cafferkey, sick with the effects of the ebola virus, for her to make a speedy and full recovery and for her family to feel the strength of our spiritual support in these trying days for them", the bishop said today as the condition of the UK's first ebola patient deteriorates.

The only other case of this kind was American doctor Ian Crozier, who had a relapse of Ebola previous year.

About nine months ago, Pauline Cafferkey was discharged from a London hospital, appearing to have defeated Ebola.

"We still think sexual transmission is rare", says Dr. Daniel Bausch, a virologist with the World Health Organization and an associate professor at the Tulane School of Public Health and Tropical Medicine.

"It was known to a few extent that the virus could persist in semen for a long time after it cleared from blood but we really didn't know how long". It doesn't cause any symptoms for the men.

The latest study was released just as a British nurse fell critically ill due to a resurgence of the Ebola virus, following her successful treatment in January.

"We don't have a great understanding of what exactly is going on in the male reproductive tract", Knust said.

The places where the virus can hide out in the body are called immune privileged sites.

He added: "The ones that we know about are in the testicles in men, the central nervous system - so that is around the brain and the spinal cord - and potentially the joint spaces, and in the chambers around your eye". The study was jointly conducted by the Sierra Leone ministry of health and sanitation, Sierra Leone ministry of defence, the World Health Organisation and the US Centres for Disease Control and Prevention.

A lab worker in protective Ebola gear.

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