The longer the Ebola epidemic continues infecting people unabated, the higher the chances it will mutate and become airborne, the UN's Ebola response chief has warned.

Anthony Banbury, the Secretary General's Special Representative, has said there is a 'nightmare' prospect the deadly disease will become airborne if it continues infecting new hosts.

His comments come as organisations battling the crisis in West Africa warned the international community has just four weeks to stop its spread before it spirals 'completely out of control'.

And the British nurse who survived the disease said the 'horror and misery' of watching young children die from the disease must be avoided 'at all costs'.

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Anthony Banbury (pictured) has warned the deadly Ebola virus could mutate and become airborne

A burial team remove a Ebola victim's body from isolation in Sierra Leone

A health worker, covered in protective equipment, hangs aprons out to dry in Monrovia, Liberia

A group of health workers spray themselves with disinfectant after removing the body of an Ebola virus victim

Mr Banbury told the Telegraph that aid workers were fighting a race against time amid fears the disease will begin to mutate.

He said: 'The longer it moves around in human hosts in the virulent melting pot that is West Africa, the more chances increase that it could mutate.

'It is a nightmare scenario, and unlikely, but it can’t be ruled out.'

He also admitted the international community had been late to respond to what was the worst disaster he had ever witnessed.

He said: 'In a career working in these kinds of situations, wars, natural disasters – I have never seen anything as serious or dangerous or high risk as this one.'

Addressing the Defeating Ebola conference in London today, British nurse Will Pooley, 29, pleaded with the world's governments to do all they could to stop children dying from the disease.

Plea: Addressing the Defeating Ebola conference in London today, Ebola survivor Will Pooley, 29, pleaded with the world's governments to do all they could to stop children dying from the disease

Visibly upset and at times overwhelmed by his emotions, Mr Pooley retold the case of a brother and sister, aged four and two, who he cared for in Sierra Leone.

He described the 'squalid' conditions they were treated in, telling how the young boy died with a pained grimace on his face lying naked in a pool of his own diarrhoea.

The little girl, described by Mr Pooley as 'beautiful', died a day after her brother, a puzzled look on her tiny face as she lay covered in her own blood.

Pleading with the world's governments, Mr Pooley, said: 'My specific fear is the horror and the misery of these deaths.

'And I just don't know what happens if that is repeated one million times and so I say, at all costs we can't let that happen.'

Mr Pooley, from Suffolk, has just returned from a life-saving mission to the U.S. where he gave blood to try and help a victim of the virus, a friend he worked with in Sierra Leone helping victims.

He became the first Briton to contract the virus after working as a volunteer nurse in Sierra Leone, which is one of the worst-hit countries of the current outbreak.

He was flown back to Britain on August 24 and recovered after being treated at an isolation unit at London's Royal Free Hospital.

A doctor receives assistance with his protective gear in Monrovia, Liberia

The number of new Ebola infections is growing exponentially - officials believe the number of new cases is doubling every few weeks, while more than 3,300 people in West Africa have so far been killed.

Save the Children have also warned five more people are infected with the virus every hour.

This week the first case of Ebola on U.S. soil was diagnosed after Thomas Eric Duncan flew into Dallas, Texas from Liberia, touching down in Brussels and Washington en route.

He is now being treated at the Texas Health Presbyterian Hospital and is said to be in a serious but stable condition.

Details of his treatment have not been revealed but Mr Duncan is reportedly not being treated with the experimental serum ZMapp used to treat aid workers with the disease, including Mr Pooley - because stocks have run out.

As many as 100 people in Texas are feared to have come into contact with 42-year-old Mr Duncan and are being contacted by health officials.

Earlier authorities had put the figure at 18, including five children - prompting parents to remove their sons and daughters from schools in Dallas.

Foreign Secretary Philip Hammond addresses the Defeating Ebola conference in central London today

The conference will hear from a group of NGOs working in West Africa, which will call on the international community to develop a six point plan to tackle the epidemic. Pictured is Foreign Secretary Philip Hammond

School administrators urged calm as none of the children have shown symptoms and are being monitored at home, where they will likely remain for three weeks.

Four members of Mr Duncan's family have been legally ordered to stay home as a precaution even though they are not showing symptoms, the Texas Department of State Health Services said in a statement on Thursday. Violating the order could result in criminal charges.

However, his quarantined girlfriend Louise, said she has not been told what to do with Mr Duncan's sweat-soaked bedclothes which remain in her home.

Victim: This week the first case of Ebola on U.S. soil was diagnosed after Thomas Eric Duncan (pictured) flew into Dallas, Texas from Liberia

She told CNN that she has been legally ordered to stay inside her Dallas apartment with her 13-year-old child and two nephews, who are both in their twenties, as they came in direct contact with the patient while he was contagious.

None of the four people quarantined are showing Ebola symptoms but Louise, who works as a home help, has been taking the group's temperature every hour.

The CDC has not told the mother what to do with Mr Duncan's sweat-soaked sheets and pillows which remain in the home. She has placed the towels he used in plastic bags and cleaned up with bleach.

The U.S. Department of health has confirmed that a patient in Honolulu, Hawaii, has been placed in isolation with suspected ebola.

The unnamed patient, who is being treated at the Queen's Medical Centre, has not yet been tested for the disease, but is displaying some symptoms.

Experts from the WHO and Imperial College, London, predict numbers will continue to climb and more than 20,000 people will have been infected by early next month.

So far, around 6,500 cases have been officially recorded, though the number of victims is thought to be under reported.

However, fears the disease may become airborne are not new.

Last month in a piece for the New York Times, Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said experts are loathe to discuss their concerns in public, for fear of whipping up hysteria.

Discussing the possible future course of the current outbreak, he warned: 'The second possibility is one that virologists are loath to discuss openly but are definitely considering in private: that an Ebola virus could mutate to become transmissible through the air.'

Dr Osterholm warned viruses similar to Ebola are notorious for replicating and reinventing themselves.

Clean up: A member of a cleaning crew in protective suit at Lowe Elementary School in Dallas, Texas on Wednesday as the schools attended by the children who came in contact with Ebola patient Thomas Eric Duncan underwent deep cleans

Currently, the virus can currently only be transmitted through close contact with bodily fluids, including blood, of an infected patient.

It means the virus that first broke out in Guinea in February may be very different to the one now terrorizing West Africa.

Pointing to the example of the H1N1 influenza virus that saw bird flu sweep the globe in 2009, Dr Osterholm said: 'If certain mutations occurred, it would mean that just breathing would put one at risk of contracting Ebola.'

In 2012, Canadian researchers found the virus could be passed via the respiratory system between pigs and monkeys - both of which have similar lungs to humans.

It was the same virus as that which is responsible for the current death toll in West Africa.

A group of locals sit at the group of flats where Thomas Duncan, the first person to be diagnosed with the virus on US soil, lived before his return to Dallas, Texas

People stand in queues at the Roberts International Airport as they attempt to leave Monrovia, Liberia

WILL POOLEY: 'I DON'T KNOW WHAT HAPPENS IF DEATHS ARE REPEATED 1 MILLION TIMES AND SO I SAY, AT ALL COSTS WE CAN'T LET THAT HAPPEN' Visibly upset and consumed by his emotions, Mr Pooley retold the case of a brother and sister, aged four and two, who he cared for in Sierra Leone. He said 'at all costs' the international community must not allow what happened to them, be repeated one million times. He said: 'They were on a specific ward alone, their mother and father had probably died. 'The blood results came back and they were both positive for Ebola, so I took them both by the hand and led them down the muddy track on to the confirmed ward. 'They were both quite weak and they struggled their way through the puddles and the mud on to the ward, squalid ward B in Kenema. Mr Pooley, 29, said the world must not let the horrific deaths of two tiny children in Sierra Leone be repeated a million times over, as he pleaded with governments to help tackle the crisis. Pictured, a health worker lifts a young victim at a medical centre in West Africa 'I popped them up on to a bed, they shared. The boy had diarrhoea and he was very weak, too weak to get up so he soiled himself. 'I cleaned him up as best I could with the limited materials available and removed his dirty clothes. 'Thereafter he lay naked on the bed, there was nothing to change him into or cover him with, the diarrhoea trickling out of him. 'His sister looked on and I encouraged her to help him take fluids regularly, she was also very weak and she tried her best. 'The next morning I came in and saw him lying as I had left him, on the bed. 'He wasn't breathing. I remember going up to him and looking at his face, his lips were drawn back in a grimace, and his eyes were vacant, lying in a pool of his own diarrhoea. 'I lifted his hand to try, just to confirm things and his whole body turned rigid and cold. 'I put him in a body bag as his sister looked on. 'She seemed more baffled than anything, not really understanding what was happening. I carried his corpse outside with the others. 'The little girl, she deteriorated the next day. Overnight, the following night she had intravenous fluids and the line came out and she bled. 'I came in the following morning and she was covered in blood. She still had a very puzzled expression on her face and she wasn't breathing. 'So I put her in a bag and left her next to her brother. She was a beautiful little girl.' Fighting back tears, Mr Pooley added: 'So my specific fear is that the horror and the misery of these deaths really fill a hole in my despair. 'And I just don't know what happens if that is repeated one million times and so I say, at all costs we can't let that happen.' Advertisement

However, other experts said it was unlikely that the disease could become airborne.

'The chances of Ebola becoming airborne are extremely small,' said Dr Jeremy Farrar, a director at Wellcome Trust.

'I am not aware of any viral infection changing its mode of transmission. This is not to say it would be impossible, but it’s important we retain a sense of proportion and not exaggerate the risks for it changing and becoming airborne. There is already enough fear and panic surrounding this epidemic.

'Of more concern is that the virus could become endemic in Western Africa, so unlike big outbreaks like this we could have smaller numbers of cases but circulating continuously. This is where we need to focus our efforts and attention – on trying to stop this outbreak before it establishes itself in Western African countries.'

Professor David Heymann, Professor of Infectious Disease Epidemiology at the London School of Hygiene & Tropical Medicine, said: 'No-one can predict what will happen with the mutation of the virus, and there is no evidence to suggest that it will become a respiratory virus. Its epidemiology is consistent with transmission via blood, bodily secretions and excretions, which is exactly the same as other past epidemics.

'Other viruses that transmit in a similar manner by blood, such as Hepatitis B and HIV, have not mutated in this manner. In order for Ebola to change, the virus would have to develop the capacity to attach to receptors in the respiratory system.'

The body of an Ebola victim is removed from a house in Monrovia, Liberia

A woman and her two children (right) are helped by doctors at the Monrovia Ebola treatment centre

Meanwhile, at the international summit convened in London today to tackle the epidemic, the International Rescue Committee (IRC), on behalf of 34 NGOs, called for a six-point plan to combat infection rates.

At today's conference Britain and Sierra Leone are proposing a new type of clinic to help slow the biggest ever Ebola outbreak.

Officials are expected to announce plans to build up to 1,000 makeshift Ebola clinics in Sierra Leone.

The new clinics will offer little, if any, treatment, but they will get sick people out of their homes, away from their families and hopefully slow the infection rate.

Currently only a fraction of Ebola patients are now in treatment centers.

'If we don't do anything, we'll just be watching people die,' World Health Organization spokeswoman Dr. Margaret Harris said.

Sierra Leone is one of the hardest-hit countries in the Ebola outbreak in West Africa, which is believed to have killed more than 3,300 people and infected at least twice as many.

Experts say the disease will continue to spread rapidly unless at least 70 percent of people who are infected are isolated and prevented from infecting other people. Dozens of Ebola treatment centers have been promised, but they could take weeks or even months to go up.

Experts are turning to such imperfect solutions because the scale of the Ebola outbreak is overwhelming the traditional response methods tried so far.

'We need to try different things because of the scale of this outbreak,' said Brice de la Vingne, director of operations for Doctors Without Borders.

'We've used these kinds of basic tents in past catastrophes but never for Ebola,' he explained. 'But right now we're screaming for more isolation centers so patients don't infect their communities.'