Three more people were put under quarantine for possible Ebola at a Madrid hospital where a Spanish nursing assistant became infected, authorities said Tuesday. More than 50 others were being monitored as experts tried to figure out why Spain's anti-infection practices failed.

The nursing assistant, part of a special team that cared for a Spanish priest who died of Ebola last month, was the first case of Ebola being transmitted outside of West Africa, where a months-long outbreak has killed at least 3,500 people and sparked social unrest. Health authorities are investigating how she became infected.

Her case highlighted the dangers health care workers face while caring for Ebola patients — officials said she had changed a diaper for the priest and collected material from his room after he died. Dead Ebola victims are highly infectious and in West Africa their bodies are collected by workers in hazmat outfits.

News of the Ebola quarantines spooked investors Tuesday because Spain is one of Europe's biggest tourist destinations. Shares of Spanish airline and hotel chain companies slumped as investors feared the Ebola case might scare away travelers.

The nursing assistant, reportedly in her 40s, was not identified to protect her privacy but nursing union officials she had 14 years of experience and authorities said she had no children. The virus that causes Ebola spreads through direct contact with the bodily fluids of an infected person.

Jose Ramon Arribas, the chief of the Carlos III hospital's infectious disease department where she was under quarantine, said she was being treated with blood plasma from an unidentified cured Ebola victim. The hospital also had an experimental anti-viral drug called Favioiravir available if needed, he said.

The nursing assistant's husband has shown no signs of having the disease but was hospitalized as a precaution, said Dr. Francisco Arnalich, head of internal medicine at the Carlos III hospital.

A nurse who also treated the priest who died Sept. 25 was put into quarantine after experiencing diarrhea but she did not have a fever. A Spanish engineer who arrived home after traveling to Nigeria was also under quarantine but his first test was negative for Ebola.

Public Health Director Mercedes Vinuesa told Parliament authorities were drawing up a list of people who may have had contact with the nurse who had Ebola.

By Tuesday, they had gotten in touch with 22 people — including relatives and personnel at the hospital in the Madrid suburb of Alcorcon where the nursing assistant went Monday with a fever. They were also monitoring 30 other members of the health care team that treated Manuel Garcia Viejo, the priest who returned from Sierra Leone and died from Ebola.

The Health Ministry's chief coordinator for emergencies, Fernando Simon, told Cadena SER radio the nursing assistant with Ebola was in stable condition and her life was not in immediate danger. Health officials said she had no symptoms besides fever.

Simon described her hospitalized husband as "OK and relatively calm."

Spainish Health Minister Ana Mato is under pressure from health workers to resign after a nurse contracted Ebola. (Andres Kudacki/Associated Press)

He rejected criticism that authorities were slow to react to the case, but about 20 health care workers at the hospital protested outside Tuesday. They called for the resignation of Spanish Health Minister Ana Mato amid claims by union officials that health workers did not receive adequate anti-infection training or the most modern Ebola protection equipment.

Rafael Perez-Santamarina, the hospital's director, said authorities did not know yet how the nursing assistant got infected despite the use of internationally recognized precautions against Ebola.

"When we finish the investigation, we will be able to say," he said.

The nursing assistant with Ebola also helped to treat 75-year-old Spanish priest Miguel Pajares, who got Ebola in Liberia, flew back to Spain, received the experimental Ebola medicine ZMapp but still died in August.

The other Spanish Ebola patient, Garcia Viejo, who was in charge of the San Juan del Dios hospital in Lunsar, Sierra Leone, was not given ZMapp because worldwide supplies ran out.

The nursing assistant went on vacation after Garcia Viejo died but health officials said she did not leave the Madrid area.

Greatest risk

Her illness illustrates that health care workers are at risk not just in the underfunded clinics of West Africa but even in the more sophisticated medical centers of Europe and the United States, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University.

"At greatest risk in all Ebola outbreaks are health care workers," he said.

More than 370 health care workers in the hardest-hit countries of Liberia, Guinea and Sierra Leone have died.

A Norwegian doctor, infected with the Ebola virus while working in Sierra Leone, arrived in Norway on Tuesday for treatment. Officials gave no details about her condition but said she was in an isolation ward at Oslo University Hospital.