WASHINGTON (AP) -- President Barack Obama calls it a "belt and suspenders" approach -- an extra level of screening at five major U.S. airports to try to catch any travelers from Ebola-ravaged countries who may be carrying the disease.
About 150 travelers a day will have their temperatures checked using no-touch thermometers, and health officials expect false alarms from fevers due to malaria.
The extra screening likely wouldn't have singled out Thomas Eric Duncan when he arrived from hard-hit Liberia last month, because he had no symptoms while traveling. Duncan, the first person to be diagnosed with Ebola in the U.S., died Wednesday in Dallas.
The disease has killed at least 3,800 people in West Africa with no signs of abating. Thursday, the presidents of Liberia, Guinea and Sierra Leone, the countries hardest hit in the outbreak, are appealing to the World Bank for more help for their nations.
"What we're paying for now is our failure to have invested in those countries before," said Francisco Ferreira, the World Bank's chief economist for Africa. They had only minimal health facilities even before Ebola hit.
In Washington on Wednesday, Secretary of State John Kerry made a plea for more nations to contribute to the fight against Ebola, saying the international effort was $300 million short of what's needed. He said nations need to step up quickly with a wide range of support, from doctors and mobile medical labs to basic humanitarian aid such as food.
The U.S. military is working to build medical centers in Liberia and may send up to 4,000 soldiers to help with the Ebola crisis. Meeting at the Pentagon with Gen. David Rodriguez and other top commanders, Obama said a top priority is to ensure the safety of those troops.
"We have unique capabilities that nobody else has," Obama said. "Our military is essentially building an infrastructure that does not exist in order to facilitate the transfer of personnel and equipment and supplies."
The new airport screening will begin Saturday at New York's JFK International Airport and then expand to Washington Dulles and the international airports in Atlanta, Chicago and Newark. The White House said checks would reach more than 9 of 10 travelers to the U.S. from the outbreak zone.
"We expect to see some patients with fever. That will cause some obvious and understandable concern at the airport," said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention.
While the government is strengthening its response, Frieden sought to tamp down expectations.
"We can't make the risk zero here. We wish we could," he said, adding that there are no plans to ban travel from the outbreak zone because that would harm efforts to send in health workers to fight the epidemic.
Ebola isn't contagious until symptoms begin, and it spreads through direct contact with the bodily fluids of patients.
Obama called the new screening measures "really just belt and suspenders" to support protections already in place. Border Patrol agents now look for people who are obviously ill, as do flight crews, and in those cases the CDC is notified.
Speaking by teleconference with mayors and local officials, Obama said he was confident the U.S. could prevent an outbreak. But he warned them to be vigilant.
"As we saw in Dallas, we don't have a lot of margin for error," the president said. "If we don't follow protocols and procedures that are put in place, then we're putting folks in our communities at risk."
Alejandro Mayorkas, deputy secretary of Homeland Security, did not rule out future measures.
"We are working very closely together across the administration and will continue to assess the risk of spread of Ebola into the U.S. and take additional measures as necessary," he said.
Around the world, health authorities scrambled to respond to the disease:
-- In Spain, doctors said they may have figured out how a nurse became the first person infected outside of West Africa in this outbreak. Teresa Romero said she remembered once touching her face with her glove after leaving the quarantine room where an Ebola victim was being treated. Romero's condition was stable.
--A social media campaign and a protest by Spanish animal rights activists failed to save Romero's dog, Excalibur. The pet was euthanized under court order out of fear it might harbor the Ebola virus.
-- In Sierra Leone, burial teams returned to their work of picking up the bodies of Ebola victims, after a one-day strike to demand overdue hazard pay.
-- Health workers in neighboring Liberia also were threatening a strike if their demands for more money and personal protective gear were not met by the end of the week. The average health worker salary is currently below $500 per month, even for the most highly trained staff.
--The World Bank estimated that the economic toll of the largest Ebola outbreak in history could reach $32.6 billion if the disease continues to spread through next year.
Associated Press writers Paul Wiseman and Josh Lederman contributed to this report.