LONDON (AFP) - A British nurse who contracted Ebola in Sierra Leone was flown to a specialist London hospital unit and in serious condition on Friday (Oct 9), nearly nine months after she was discharged, due to an "unusual late complication".

Nurse Pauline Cafferkey, who voluntarily went to the west African country to treat Ebola patients, was flown from a Glasgow hospital to London's Royal Free Hospital, which houses Britain's only isolation ward for Ebola patients.

She had been admitted to hospital in Glasgow on Tuesday after feeling unwell, and was now "is in a serious condition", the hospital said.

It added: "The Ebola virus can only be transmitted by direct contact with the blood or bodily fluids of an infected person while they are symptomatic so the risk to the general public remains low."

The Scottish health authorities were to get in touch with a small number of Ms Cafferkey's close contacts as a precaution.

She was transferred early on Friday "due to an unusual late complication of her previous illness", said Professor Paul Cosford, medical director at Public Health England agency.

"She was transported in a military aircraft under the supervision of experts. She will now be treated in isolation in line with nationally agreed guidelines.

"The Scottish health authorities will be following up on a small number of close contacts of Pauline's as a precaution."

Dr Emilia Crighton of the Glasgow health board confirmed: "Pauline's condition is a complication of previous infection with the Ebola virus."

She stressed that the risk to the public was very low.

Ms Cafferkey was diagnosed with Ebola in December after returning to Glasgow from Sierra Leone.

She spent almost a month in an isolation unit at the Royal Free Hospital and was treated with an experimental anti-viral drug and blood from survivors of the Ebola disease.

Details of her condition have not been disclosed for reasons of patient confidentiality.

Dr Ben Neuman, a lecturer in virology at the University of Reading, said Ms Cafferkey could be only the second known case of "reactivated" Ebola.

"Over the past few years, there has been mounting evidence of the mental and physical problems in Ebola survivors that can last for years after the virus is cleared from the bloodstream," he told the Science Media Centre in London.

"The newly discovered twist on this post-Ebola syndrome is that, in some cases, the health problems - often including damage to the eyes and joints - is actually caused by live Ebola virus growing in bodily fluids in some of the less accessible compartments of the body."

On Wednesday, the World Health Organization (WHO) said there had been no new confirmed Ebola cases in the past week - the first such lull in a year and a half.

The deadliest-ever Ebola outbreak since the virus was identified in central Africa in 1976 has killed 11,312 of the 28,457 people infected since December of 2013, according to the latest WHO figures.

Nearly all the victims have been in Guinea, Liberia and Sierra Leone.