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 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.

Meningitis is a condition in which a bacteria or virus causes inflammation of tissues overlying the brain. It can be caused by many different viruses and bacteria.

Jacobs 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.

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Cafferkey was admitted to an isolation unit at London's Royal Free Hospital 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 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.

"This is an unprecedented situation," said Nathalie MacDermott, an Ebola expert and clinical research fellow at Imperial College London. "We have not before seen a re-emergence of the virus in the form of meningitis."

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.

MacDermott said it was important that all those involved in caring for survivors "are aware of this possible complication and remain vigilant for it".

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 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.