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Infection scene: Madrid's Hospital Carlos III where the nurse infected with Ebola worked. Photo: AFP

Madrid: A Spanish nurse, who is the first person to contract Ebola outside Africa, may have touched her face with the gloves of her protective suit while caring for a priest who died of the disease, a doctor treating her said.

The nurse, Teresa Romero, was being treated for the deadly infection at a Madrid hospital while Spanish officials launched an investigation into how she contracted Ebola despite strict protocols for handling contagious patients.

The virus, which the World Health Organisation said had killed 3879 people by October 5 in West Africa since March in the largest outbreak of the disease on record, causes haemorrhagic fever and is spread through direct contact with body fluids from an infected person.

Risky patient: Miguel Pajares was transferred from West Africa to Spain after contracting Ebola. Photo: Reuters

A Liberian man who was the first person diagnosed with Ebola in the United States died in hospital on Wednesday and the US government has ordered extra screenings at five major airports.

The World Health Organisation said it saw no evidence of the disease being brought under control in Liberia, Sierra Leone and Guinea, with neighbouring countries being told to prepare for the disease to spread across their borders.

Britain said it was sending extra troops, aircraft and a naval vessel to Sierra Leone to help stem the spread. The deployment will see 750 military personnel help set up treatment centres and a training facility. Three helicopters and a 100-bed naval hospital will also be sent to the region.

Flew from Liberia: Thomas Eric Duncan, the first patient in the US diagnosed with Ebola, has died. Photo: AP

While Ms Romero is the only confirmed Ebola case in Spain aside from two priests who contracted the disease in Africa and died, more than 50 other people who may have had contact with the virus in the country are being monitored, including primary health care and hospital staff, European officials said.

"She has talked to me about the gloves, she touched her face with the gloves. That's what she remembers and what she has told me three times," German Ramirez, one of the doctors at Carlos III hospital where the nurse is being treated, said on Wednesday.

The nurse took leave from work immediately after Spanish missionary Manuel Garcia died on September 25. Wearing a full protective suit, she had entered the priest's room once while he was alive and once after his death to clean the room.

"I believe the error was made when taking off the suit," she told Spain's El Pais newspaper. "I see that as the most critical moment, when something could have happened. But I'm not sure."

Health worker union officials said Ms Romero alerted hospital staff three times to say she had a fever and a rash, but because her temperature had not gone above 38.6 degrees the hospital did not see her as a risk.

Ms Romero found out she had the disease by looking at the news online while she was waiting for the result of her test, she told Cuatro television station.

"I asked the doctor for the result and he didn't answer in a very clear way and that's when I started to suspect," adding she then looked at her phone to find there was a positive case of Ebola in Spain.

Health authorities on Thursday put down the dog, a labrador-type breed called Excalibur, who lived with the nurse and her husband in a suburban Madrid flat, saying it posed a biological risk and there was evidence dogs could carry the virus.

The couple are two of six people under observation in the sealed-off sixth floor of the hospital in Madrid. The rest of the people, including other nurses who cared for the infected priests, have initially tested negative for Ebola, health authorities said.

Spanish Prime Minister Mariano Rajoy defended his country's health authorities and urged people not to panic. He said the investigation into how the infection had occurred was a priority and was still under way.