London - A volunteer nurse who contracted Ebola in west Africa was being treated at an isolation unit in a specialist London hospital on Tuesday as infection rates increased in eastern Sierra Leone.
The woman, who returned Sunday from a treatment facility in Kerry Town in Sierra Leone run by the Save the Children charity, was transferred overnight from a Glasgow hospital in a Royal Air Force plane.
It is the first time someone has tested positive for Ebola in Britain and she is the second to be treated for the virus after fellow nurse William Pooley who made a full recovery earlier this year.
The world's deadliest-ever outbreak, which has killed 7,842 people out of 20,081 cases, has been centred on Sierra Leone, Liberia and Guinea.
Meanwhile, another person returning from west Africa was being treated in Cornwall in southwest England and a second person, a healthcare worker coming back, was to be tested in Aberdeen, Scotland.
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Around 100 have been tested for Ebola in hospitals across England so far this year, with all of them negative so far.
The new case is being treated at the Royal Free hospital in London, which has a high-level isolation unit ready to handle Ebola cases.
She had travelled to Glasgow from Sierra Leone on Sunday, via Casablanca in Morocco and health authorities are contacting the people she was travelling with.
The National Health Service worker was admitted to hospital in Glasgow on Monday after feeling feverish, and placed in isolation.
On Tuesday she was transferred by ambulance to Glasgow Airport where she was seen walking into a quarantine tent.
Surrounded by health workers in full protection suits, she was wheeled onto a military transport plane and flown to London, where she is being treated in a ward equipped with its own ventilation system to prevent contagion.
"This particular individual has symptoms of fever but she did not have the symptoms that make us worried about transmission before she was in the isolation facility in Glasgow," said Professor Paul Cosford from the Public Health England agency.
"We are confident the risk to others is low," he told BBC radio.
Ebola is transmitted through bodily fluids.
Prime Minister David Cameron will chair a meeting of the government's emergency contingencies committee later Tuesday.New cases in Sierra Leone
Sierra Leone's deputy government spokesman Abdulai Bayratay said the nurse did not have Ebola symptoms when she left.
"The screening process she went through at the Lungi International Airport was of quality standard and as far as was detected, she left the country without any symptoms of Ebola," he told AFP.
"It is an unfortunate development and we wish her a quick recovery and our regards go to her family and friends who have supported her in this great sacrifice to humanity."
Bayratay said he did not feel the case would deter other international volunteer health workers from coming to Sierra Leone
"The input of foreign health workers has been an important cog in the Ebola fight," he said.
In Sierra Leone, a five-day Christmas lockdown in the north aimed at preventing new Ebola infections ended on Monday.
However, Ebola infections have increased in the diamond-rich Kono district in the country's east, where the infection rates had been decreasing, the national broadcaster said.
Quoting updates from the National Ebola Response Centre, it said Kono had recorded 21 new Ebola cases on Friday and Saturday.
Meanwhile scientists said Tuesday that insect-eating bats that inhabited a hollow tree in a remote village in Guinea may have been the source of the epidemic.
The first death was that of a two-year-old boy died in the village of Meliandou in December 2013.
Reporting in the journal EMBO Molecular Medicine, scientists led by Fabian Leendertz at Berlin's Robert Koch Institute delved into the circumstances surrounding this first fatality.
The finger of suspicion points at insectivorous free-tailed bats, Mops condylurus in Latin, that lived in a hollow tree 50 metres (yards) from the boy's home, they said.
The German team said evidence that this species helped unleash the present epidemic was strong but not 100 percent.