Madrid, Oct 8 (IANS/EFE): Spain's Health Minister Ana Mato Wednesday said a probe has been opened into the cause of the first case of Ebola virus disease contracted outside Africa, and stressed all precautions were taken during the treatment of two affected missionaries repatriated to Spain last summer.

"We are using all means to avoid contagion," Mato told parliament and said Spain has followed all the protocols recommended by the World Health Organization.

Spanish Prime Minister Mariano Rajoy told parliament, "We have to be watchful, but remain calm".

Spanish nurse Teresa Romero, the first person to contract Ebola outside Africa, is being treated at Madrid's Carlos III Hospital, where her husband Javier Limon, who has no symptoms, is also in quarantine.

Mato said Wednesday there was no evidence of Ebola symptoms in people who were in contact with Romero, and added that another health worker was being tested for the disease.

In all, three health workers are in quarantine at the hospital, along with a Spanish engineer who had fever after returning from Nigeria.

Some 52 people, including relatives and health workers close to Romero, are under observation in their homes.

Romero was infected with the virus while taking care of two Spanish missionaries, Manuel Garcia Viejo and Miguel Pajares, who were repatriated last summer to Madrid from Sierra leone and Liberia respectively and who died from the disease.

Romero, who worked at the Carlos III Hospital where the two missionaries were treated, felt ill with fever Sep 30 but she did not consult a doctor until last Sunday after ending her holidays, during which she stayed mainly at home, according to her husband.

Officials said she entered Garcia Viejo's room twice, once to change a diaper and another time to disinfect the room after the missionary died.

Doctors have said Romero's response to treatment was "favourable" but have called for "caution". She is being treated with an antiviral and antibodies taken from a Spanish nun who contracted the disease in Liberia and recovered.

The European Commission has urged Spain to clarify the circumstances in which Romero was infected.

Experts from the 28 European Union member nations Wednesday held a teleconference to discuss the case, which has raised alarm in Europe.

Ebola spreads through direct contact with blood and bodily fluids of infected persons or animals, causing fever and severe bleeding.

Since the outbreak of the disease in West Africa last March, the most virulent known until now, it has caused around 3,439 known deaths from 7,492 cases, mainly in Guinea Conakry, Liberia and Sierra Leone.