Spain is investigating how a nurse in Madrid could have become infected with Ebola, sparking fears of the first outbreak outside Africa.

The inquiry was launched as the EU demanded answers from the Spanish authorities about how the disease could have spread in a specialist Madrid unit where the woman treated two elderly Spanish missionaries who died from the virus.

Tests confirmed she has the disease, government officials said, making her the first person to contract the virus outside Africa.

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The 40-year-old began to feel ill on September 30 while on leave after treating the two patients in the isolation unit of Madrid’s La Paz-Carlos III hospital. But she did not go to hospital until Sunday – five days later – complaining of a fever, government officials said.

She is now being treated in the same unit.

Health officials said they were trying to find out who she came into contact with, and were monitoring 30 people – including co-workers and her husband – for Ebola symptoms.

The infection also sparked questions about how safety procedures were applied when treating the two missionaries.

“People are freaked out,” a cardiologist at the hospital said. “We cannot understand how someone who was wearing a double protection suit and two pairs of gloves could have been contaminated.”

She claimed Spain was not up to dealing with the haemorrhagic fever and questioned the decision to repatriate the missionaries.

The nurse had treated Spanish priest Miguel Pajares, 75, who was infected with Ebola in Liberia and died on August 12, as well as Manuel Garcia Viejo, 69, who was repatriated from Sierra Leone and died on September 25.

Pajares was the first patient in the current Ebola outbreak to be evacuated to Europe for treatment.

The infected nurse is believed to have contracted the virus six weeks later while caring for Garcia Viejo, whose room officials said she visited twice, once to treat him and once to clean the room.

Both missionaries were treated in the isolation unit at the hospital, and the medical team that cared for them were closely monitored.

In Brussels on Tuesday an EU spokesman said the European Commission had written to the Spanish health ministry demanding an explanation.

“Some large countries are not doing enough,” says US President Barack Obama.

The case followed a wake-up call on Ebola from US President Barack Obama, who warned on Monday that “some large countries are not doing enough” to tackle the epidemic.

The Ebola virus causes fever, muscle pain, vomiting, diarrhoea and sometimes internal and external bleeding.

It spreads through bodily fluids, and the only way to stop an outbreak is to isolate those who are infected. There is no vaccine to prevent it, but one possible treatment, dubbed ZMapp, has been fast-tracked for use.

Ebola has caused 3439 deaths out of 7478 cases across five west African nations – Liberia, Guinea, Sierra Leone, Nigeria and Senegal, according to the latest WHO tally.

Patients have been treated for the disease in Europe and the US, but until now all the cases stemmed from people who caught the virus in west Africa.

-AAP