A Scottish nurse who contracted and initially recovered from Ebola, but then suffered relapsing illness, has meningitis caused by the virus persisting in her brain, doctors treating her said on Wednesday.

Pauline Cafferkey was not reinfected with the Ebola virus, doctors said, but it had remained in her body since her initial recovery and had re-emerged to cause life-threatening complications.

"The virus re-emerged around the brain and around the spinal column to cause meningitis," said Michael Jacobs, an infectious diseases consultant who has been treating Cafferkey in London.

He said Cafferkey had been critically ill and at one stage last week was at high risk of dying, but had now made a significant improvement and looked likely to be able to recover.

Cafferkey was transferred to an isolation unit at the Royal Free Hospital in London on Oct. 9 after suffering an apparent relapse.

She was the first person to have been diagnosed with Ebola on British soil when she contracted the disease in December 2014 and spent several weeks in an isolation unit at the Royal Free before making a recovery and being discharged.

Cafferkey's case has generated worldwide interest, as experts say there has never been a documented case like it.

The Ebola virus has killed more than 11,300 people in West Africa in an unprecedented epidemic over the past year, which also left some 17,000 survivors of the disease.

Jacobs said on Wednesday Cafferkey is now able to talk and eat a little, but is still in bed, faces a long recovery and will probably need to remain in hospital for some time.

The nurse, who originally contracted Ebola while working in Sierra Leone, is currently being treated with an experimental antiviral drug known as GS5734 being developed by the U.S. drugmaker Gilead Sciences.

Gilead confirmed that its compound "is currently being provided to a female patient in the United Kingdom".

Jacobs said this treatment was being carried out with Cafferkey's full consent, and added that he and his medical team did not yet know whether it would work.

"We're very hopeful that Pauline will slowly make a full recovery," he said, adding that he hoped Cafferkey's own immune system would eventually fight off and clear the virus.

The Ebola virus is known to be able to persist in various tissues in the body after it has cleared the bloodstream, but scientists are only now starting to find out more about how long it can survive and where, whether and when it might re-emerge.

Asked if Cafferkey posed a contagion risk, Jacobs stressed that her current illness was very different from the Ebola haemorrhagic fever she had in December 2014, with the virus far less likely to be shed and spread to others.

"The infection risk is completely different," he said. "But we can't call it zero, so we're taking a precautionary approach."

(Reporting by Estelle Shirbon and Kate Kelland; Editing by Tom Heneghan)