Dallas Ebola patient 'fighting for his life'

The Ebola patient hospitalized in Dallas is "fighting for his life," a top US health official said on Sunday, a day after the man's condition worsened from serious to critical.

"The man in Dallas, who is fighting for his life, is the only patient to develop Ebola in the United States," Dr. Tom Frieden, director of the Centers for Disease Control in Atlanta, told CNN's "State of the Union."

Frieden said that in the affected parts of West Africa, where ebola has killed more than 3,000 people, the disease is spreading so rapidly it is difficult for health officials to keep up.

He said he was confident that the virus would not spread widely in the United States.