Associated Press
The Ebola Virus is shown in this undated electron micrograph photo provided by the Centers for Disease Control and Prevention in Atlanta, Ga., Thursday, May 11, 1995.

WASHINGTON — Republican lawmakers indignantly criticized the government response to the arrival of Ebola on U.S. shores Thursday in a tense hearing on Capitol Hill. Top public health officials defended their actions as public unease grew over the possibility of the deadly virus spreading widely here — something health experts insisted was a remote possibility.

"People are scared," said Rep. Fred Upton, R-Mich., chairman of the House Energy and Commerce Committee. "People's lives are at stake, and the response so far has been unacceptable."

Dr. Thomas Frieden, head of the Centers for Disease Control and Prevention, said he remained confident in the ability of the U.S. health care system to combat Ebola.

"Working with our partners we have been able to stop every prior Ebola outbreak, and we will stop this one," he said. "We know how to control Ebola, even in this period."

But even as he offered reassurances Frieden raised alarms of his own about threats to this country if the raging epidemic in West Africa, which has already claimed more than 4,000 lives, cannot be stopped.

"There are no shortcuts in the control of Ebola and it is not easy to control it. To protect the United States we need to stop it at its source," he said.

"One of the things I fear about Ebola is that it could spread more widely in Africa. If this were to happen it could become a threat to our health system and the health care we give for a long time to come."

Fears over the disease are on the rise as two nurses tested positive after caring for a patient in Dallas who died of the disease. One of them was cleared by the CDC to travel on a commercial plane after registering a slightly elevated fever, officials disclosed on Wednesday.

Dr. Anthony Fauci, director of the National Institutes of Health National Institute of Allergy and Infectious Disease, told lawmakers Thursday that the first nurse to fall ill, Nina Pham, was being transferred to the NIH in Bethesda, Maryland, for treatment. The second nurse, the one who took a commercial flight before being diagnosed, has been transferred to Emory University Hospital in Atlanta near the CDC.

Lawmakers had tough questions on hospital protocols and travel restrictions. Several Republicans suggested a partial travel ban for people who've been in West Africa.

Election-year politics were evident in the hearing room with midterm balloting less than a month away. Two House members in highly contested Senate races, Rep. Cory Gardner, Republican of Colorado, and Rep. Bruce Braley, Democrat of Iowa, left the campaign trail to appear at Thursday's hearing.

President Barack Obama canceled travel plans to stay at the White House and oversee government's response to the Ebola problem.