WASHINGTON — Raising fresh concern around the world, a nurse in Spain on Monday became the first person known to catch Ebola outside the outbreak zone in West Africa.
In the United States, President Barack Obama said the government was considering ordering more careful screening of airline passengers arriving from the region.
In dealing with potential Ebola cases, Obama said, "we don't have a lot of margin for error."
Already hospitalized in Dallas, a critically ill Liberian man, Thomas Duncan, began receiving an experimental drug. But there were encouraging signs for an American video journalist who returned from Liberia for treatment. Ashoka Mukpo, 33, was able to walk off the plane before being loaded on a stretcher and taken to an ambulance, and his father said his symptoms of fever and nausea appeared mild.
"It was really wonderful to see his face," said Dr. Mitchell Levy, who talked to his son over a video chat system at Nebraska Medical Center.
In Spain, the stricken nurse had been part of a team that treated two missionaries flown home to Spain after becoming infected with Ebola in West Africa. The nurse's only symptom was a fever, but the infection was confirmed by two tests, Spanish health officials said. She was being treated in isolation, while authorities drew up a list of people she had had contact with.
Medical workers in Texas were among Americans waiting to find out whether they had been infected by contact with Duncan, the African traveler.
In Washington, the White House continued to rule out any blanket ban on travel from West Africa, where the virus has killed more than 3,000 people.
People leaving the outbreak zone are checked for fevers before they're allowed to board airplanes, but the disease's incubation period is 21 days and symptoms could arise later.
Airline crews and border agents already watch for obviously sick passengers, and in a high-level meeting at the White House, officials discussed potential options for screening passengers when they arrive in the United States as well.
Obama said the U.S. will be "working on protocols to do additional passenger screening both at the source and here in the United States." He did not outline any details or offer a time line for when new measures might begin.
The Obama administration maintains that the best way to protect Americans is to end the outbreak in Africa. To that end, the U.S. military was working Monday on the first of 17 promised medical centers in Liberia and training up to 4,000 soldiers this week to help with the Ebola crisis.
About 350 U.S. troops are already in Liberia, the Pentagon said, to begin building a 25-bed field hospital for medical workers infected with Ebola. A torrential rain delayed the start of the job on Monday.
The virus has taken an especially devastating toll on health care workers, sickening or killing more than 370 in the hardest-hit countries of Liberia, Guinea and Sierra Leone — places that already were short on doctors and nurses before Ebola.
Texas Gov. Rick Perry urged the federal government to begin screening air passengers arriving from Ebola-affected nations, including taking their temperatures.
Perry stopped short, however, of joining some conservatives who have backed bans on travel from those countries.
Federal health officials say a travel ban could make the desperate situation worse in the afflicted countries, and White House spokesman Josh Earnest said it was not currently under consideration.