ATLANTA, Ga. (ABC News/CNN) -- An American doctor flown to the U.S. after being infected with Ebola in Liberia "seems to be improving" after receiving an experimental antibody serum, according to the director of the Centers for Disease Control and Prevention on Sunday.
"It's encouraging that he seems to be improving," Thomas Frieden said of Dr. Kent Brantly on CBS' "Face the Nation" on Sunday. "That is really important, and we are hoping he will continue to improve."
"We praise God for the news that Kent's condition is improving," said a Sunday statement from Samaritan's Purse, the Christian charity that employs the 33-year-old Brantly. He is the first known patient with the deadly virus to be treated on U.S. soil.
Brantly's one of two Americans sickened by the deadly viral hemorrhagic fever last month while on the front lines of a major outbreak in West Africa. Brantly's plane, equipped with an isolation unit, landed at Dobbins Air Reserve Base in Georgia on Saturday and he was quickly rushed to Atlanta's Emory University Hospital.
Photographs and video from Emory showed medical personnel in a white, full-body protective suits helping a similarly-clad Brantly emerge from an ambulance and walk into the hospital.
"He was ambulatory, being able to talk, converse and get up. So that was encouraging," said Bruce Johnson, Samaritan Purse's president.
Medical experts familiar with the ravages of the Ebola disease said they were "pleasantly surprised" that Brantly was able to walk - but also pleased that he seemed to be doing well.
Dr. William Schaffner, an infectious disease specialist at the Vanderbilt University School of Medicine, said he felt "guardedly optimistic," since Ebola usually advances quickly and Brantly had shown signs of the disease for at least a week.
"The first thing we all said 'Whoa he's not on a vent,'" Schaffner said of realizing that Brantly did not need a ventilator to help him breathe. "In general [with] Ebola is ... you progress on a downhill course. If you're at this point and you're holding your own you're entitled to be optimistic."
Dr. Stephen Morse, a professor of Epidemiology at the Columbia University Mailman School of Public Health, said although it does not guarantee Brantly will fully recover, the fact that he could walk 10 days after showing Ebola symptoms is a "very good sign."
The same specially-outfitted plane used to transport Brantly will now be used to bring the other infected American aid worker, Nancy Writebol, to Atlanta for treatment on Tuesday.
Athough Brantly was given an unknown serum - the purpose and effects of which weren't immediately publicized - on his flight to the U.S., there is no known cure for Ebola. To treat Brantly and Whitebol, doctors at Emory are focusing on providing "supportive care" by stabilizing the patients' blood pressure, respiration and taking other measures, such as blood transfusions and dialysis, to keep them stable.
"We just have to keep the patient alive long enough in order for the body to control this infection," said Emory's Dr. Bruce Ribner, who is supervising the treatments.
Brantly's wife Amber was able to visit with her husband Sunday for the first time since he became ill and said the family was "rejoicing" over her husband's arrival back in the U.S.
"We are very grateful to the staff at Emory University Hospital, who have been so nice and welcoming to us. I was able to see Kent today," said Amber Brantly. "He is in good spirits. He thanked everyone for their prayers and asked for continued prayer for Nancy Writebol's safe return and full recovery."
While Ebola is a highly fatal disease, experts emphasized that an outbreak of the virus is incredibly unlikely within the U.S.
Ebola does not easily spread from person to person. The virus is transmitted through bodily secretions, including blood and urine, or through contaminated surfaces. As a result, the group most at risk is medical staff.
The hospital containment units used to treat Brantly and Writebol were created by Emory along with the CDC and are specifically designed to isolate the infected patients and protect health workers and the public from the disease, officials said.
More than 700 people have died after contracting Ebola in Liberia, Sierra Leone and Guinea since cases were first reported in March, according to the World Health Organization.