The Spanish nurse who contracted Ebola while caring for two infected priests in a Madrid hospital, becoming the first person to contract the virus outside West Africa, appears to have overcome the deadly disease, the government said.

Tests on Teresa Romero, 44, hospitalised earlier this month with a high fever and treated in an isolation unit in a specially-adapted hospital in central Madrid, gave a negative result for the virus on Sunday, it said in a statement.

Usually patients must take another test within 72 hours to be given the all-clear from the disease, which has killed thousands in West Africa. The hospital will take another test in a few hours' time, the government statement said.

Romero was treated with a drip of human serum containing antibodies from Ebola sufferers who had survived the disease and other drugs which a government spokeswoman declined to name. One was the experimental anti-viral medicine favipiravir, El Mundo newspaper said.

Romero is the only known sufferer of Ebola in Spain. There are a further 15 people in hospital, including Romero's husband, under observation for signs of the disease.

Ebola has killed at least 4,546 people in Liberia, Sierra Leone and Guinea in the recent outbreak, the World Health Organization said on Friday.

Spain has given its permission for the United States to use U.S. military bases in an operation to send up to 4,000 troops to West Africa to help contain the disease.

Spain will approve requests for the United States to use the bases at Rota near Cadiz and at Moron de la Frontera near Seville in southern Spain, the Ministry of Defence said in a statement on Saturday.