The deadly Ebola virus is “scary,” but “we can stop it,” Centers for Disease Control and Prevention Director Tom Frieden said today.

The day after an American doctor who contracted the virulent disease while doing missionary work in Liberia was flown into the United States for treatment, the CDC chief talked about the task ahead on CBS’ “Face the Nation.”

Kent Brantly was being treated in a special isolation unit at Emory University Hospital in Atlanta after arriving Saturday at Dobbins Air Reserve Base in Georgia. It’s the first known time anyone infected with the virus has been brought into the country.

“We’re hoping he’ll continue to improve,” Frieden–who also was scheduled to appear on Sunday shows on ABC, NBC, and Fox–said on CBS. “But Ebola is such a scary disease because it’s so deadly. I can’t predict the future for individual patients.”

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A second American missionary infected with the virus, Nancy Writebol, was expected to arrive in the U.S. within a few days.

Brantly and Writebol both were serving in Liberia as medical missionaries. The virus has killed at least 729 people and sickened more than 1,300 in the West African nations of Liberia, Guinea, and Sierra Leone.

Frieden said he is optimistic. “We know how to stop Ebola,” the CDC official said on CBS. “It’s not easy, but it can be done.”