American aid worker stricken with Ebola being treated in U.S

"It's encouraging that he seems to be improving - that's really important - and we're hoping he'll continue to improve," said Dr. Tom Frieden, director of the U.S. Centers for Disease Control in Atlanta.

Dr. Kent Brantly was able to walk, with help, from the ambulance that transported him on Saturday to Atlanta, where he was being treated in a special isolation unit at Emory University Hospital.

Frieden said it was too soon to predict whether Brantly would survive the deadly disease.

He said it was unlikely that Brantly's wife and two children, who visited him in Liberia, had contracted the disease because he was not exhibiting symptoms when they were there.

(Reporting by Doina Chiacu; Editing by Jim Loney)