Image caption Pauline Cafferkey previously spent a month in the specialist isolation unit

Nurse Pauline Cafferkey remains in a "serious condition" after being readmitted to the isolation unit where she was previously treated for Ebola.

She was returned to the Royal Free Hospital in London after tests indicated the virus is still present in her body.

It is not thought the 39-year-old nurse is contagious.

She was initially admitted to a hospital in Glasgow on Tuesday after feeling unwell.

Ms Cafferkey, from Cambuslang in South Lanarkshire, spent almost a month in isolation at the beginning of the year after contracting the virus in December 2014.

Bodily tissues can harbour the Ebola infection months after the person appears to have fully recovered.

Media playback is unsupported on your device Media caption BBC News looks at why some Ebola survivors suffer a flare up of symptoms

Ms Cafferkey was transferred to the Royal Free Hospital in the early hours of Friday morning due to an "unusual late complication" in her illness.

Dr Ben Neuman, a virologist from the University of Reading, told BBC Radio's Good Morning Scotland programme that the outlook for Ms Cafferkey was good and it was unlikely the virus remained infectious.

He said: "Once the virus is removed from the blood once, it tends to retreat into the hard-to-access components of the body. It'll hide in places like the back of your eye or breast milk."

He said the effects of the virus on the body could last for up to two years, although it was difficult to know how long it could actually persist.

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He added: "The nice news here is that she's beaten the virus once so she can probably beat it again.

"The odds are that she has actually inherited a lucky set of genes and these are probably what protected her the first time and probably what will keep her safe the second time regardless of any treatment. The outlook's good."

Ebola is passed on through bodily fluids. It is not transmitted through casual contact.

Last week Ms Cafferkey, who works at the Blantyre Health Centre, was in London receiving an award at the Pride of Britain ceremony which recognised the risks aid workers took with their own health.

There are not thought to be any concerns about contact she had with people at the event but health officials in Scotland are focusing on who she had seen since her return home.

The nurse had returned to her role with NHS Lanarkshire in March and was last at work on 1 October, the health board said.

On Monday, she visited a primary school in East Kilbride in South Lanarkshire to give a presentation and thank pupils for money they had raised.

South Lanarkshire Council said parents had been reassured that Ebola cannot be spread through ordinary social contact.

Ms Cafferkey contracted Ebola while working as a volunteer with Save the Children at a treatment centre in Kerry Town, in Sierra Leone.

She was diagnosed on 29 December last year, after returning to Glasgow via London.