Kent Brantly, one of two American aid workers infected with the deadly virus as they helped battle an outbreak in West Africa, arrived Saturday at a US air base in Georgia.
Clad in a white biosuit, Brantly was seen walking gingerly into Emory University hospital in Atlanta, which has a cutting edge isolation unit used to treat victims of infectious diseases.
"It's encouraging that he seems to be improving. That's really important, and we're hoping he'll continue to improve," said Tom Frieden, the director of the Atlanta-based Centers for Disease Control.
"But Ebola is such a scary disease because it's so deadly," he added, speaking on CBS's Face the Nation.
More than 700 people have died in West Africa during the current outbreak. Since the virus emerged in 1976 it has killed two-thirds of those infected.
"The plain fact is, we can stop it. We can stop it from spreading in hospitals and we can stop it in Africa," Frieden said.
"In fact, we have stopped every previous outbreak, and I'm confident we can stop this one," he said.
"But it's going to be hard because it's spread through so many countries and there's such a risk of further spread in Africa," he said.
Brantly's wife Amber asked for people to pray for her husband's recovery and that of those stricken with the virus in Liberia.
"I spoke with him, and he is glad to be back in the US. I am thankful to God for his safe transport and for giving him the strength to walk into the hospital," she said in a statement.
Christian missionary worker Nancy Writebol is expected to be airlifted back to the United States in the coming days by the same method as Brantly.