American Doctor With Ebola Received Experimental Antibody Serum Before U.S. Arrival

— -- An American doctor infected with Ebola received an experimental antibody serum before being flown to the U.S. and his condition is "improving," according to the aid group Samaritan's purse.

Dr. Kent Brantly, 33, was evacuated to the U.S. after contracting Ebola while treating infected patients in Monrovia, Liberia. Brantly and a second American, Nancy Writebol, were both working with in a clinic for Ebola patients in Liberia, when they were infected with the deadly virus last month.

Brantly was described today as "improving," by the Samaritan's Purse, the aid group Brantly worked for in Africa.

Athough Brantly was given an unknown serum, there is no known cure for Ebola and to treat patients doctors have focused on providing supportive care by stabilizing a patient's blood pressure, respiration and other vital signs.

Brantly's wife Amber Brantly was able to visit with her husband for the first since he became ill and said the family is "rejoicing" over her husband's arrival.

"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."

Brantly arrived via a specially outfitted air ambulance Saturday and is being held in a specialized isolation ward in Emory University Hospital in Atlanta, Georgia. He is the first known patient with Ebola to be treated in the U.S.

The plane that will carry Writebol will leave the U.S. for the West African country later today and is expected to return Tuesday, a U.S. official told ABC News.

The private air ambulance is scheduled to take off today and arrive in Liberia after one stopover, the official said. The plane will then bring aid worker Nancy Writebol to Dobbins Air Reserve Base in Marietta, Ga., and is expected to land midday Tuesday.

The same plane brought Brantly to Georgia on Saturday.

Full Coverage of the Ebola Outbreak

Ebola Outbreak Feeds on Fear, Anger, Rumors

Why Experts Were Surprised Ebola-Infected Doctor Could Walk

"We thank God that they are alive and now have access to the best care in the world," Franklin Graham, president of Samaritan's Purse, said in a statement.

While Ebola is a highly fatal disease, an outbreak of the virus is incredibly unlikely within the U.S. The containment units Brantly and Writebol will be treated in are designed to isolate infected patients and protect health workers and the public from the disease.

The director for the Centers for Disease Control, Tom Frieden, told ABC News the isolation unit at Emory University Hospital, where both Brantly and Writebol will be treated, was one of only four in the nation.

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.

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.

Family of American Doctor With Ebola Optimistic About His Recovery

How Doctors Can Transport Ebola-Stricken Americans More Than 5,000 Miles

What Happens When Ebola Patients Arrive in the US