USA officials defend ebola response

Health officials said Thursday they still don't know how two Dallas nurses caught Ebola from a patient, as criticism increased from lawmakers who questioned whether the U.S. is prepared to stop the deadly virus from spreading in the country.

The revelation that one of the hospital nurses was cleared to fly on a commercial airline the day before she was diagnosed raised new alarms about the American response to the Ebola outbreak in West Africa. The death toll is expected to climb above 4,500 in Africa, all but a few within Liberia, Sierra Leone and Guinea, the World Health Organization said.

In Sierra Leone, the government announced the virus had infected two people in the last part of the country that had been free of the disease, in the mountainous north, despite aggressive steps to keep it at bay.

President Barack Obama authorized a call-up of reserve and National Guard troops in case they are needed. His executive order would allow more forces than the up-to 4,000 already planned to be sent to West Africa, and for longer periods of time.

A ban on travel to the U.S. from the Ebola-stricken countries, sought by some Republican lawmakers, is not under consideration, White House spokesman Josh Earnest said Thursday.

The president met into the evening with top aides and health officials at the White House, declaring afterward that he had no "philosophical objection" to imposing a travel ban on West Africa but had been told by health and security experts that it would be less effective than measures already in place — and perhaps would be counterproductive.

He said a ban could result in people trying to hide where they were coming from and thus becoming less likely to be screened.

He said it may be appropriate to appoint an additional person to lead the anti-Ebola effort in the U.S., a response to calls that he name an Ebola "czar."

U.N. Secretary-General Ban Ki-moon made another urgent appeal for funds, saying that a trust fund he launched to provide fast and flexible funding for the fight against Ebola has only received $100,000 of the $20 million pledged.