The Nebraska doctors treating an American doctor who became infected with the Ebola virus while working in West Africa said Sunday that he is making progress, but it is still unclear whether he will recover.

Dr. Rick Sacra, 51, arrived at the Nebraska Medical Center on Friday for treatment in the hospital's specialized isolation unit.

Sacra remains very tired and stable, but was more alert Sunday, Dr. Phil Smith, one of the doctors treating Sacra, said.

"We are encouraged by what we see, but it's too early to say he has turned a corner," Smith said.

Sacra has been helping with his own treatment by providing information about Ebola to the doctors because he saw it in Africa.

Smith also said Sacra is receiving an experimental drug that is different than the one given to the two earlier American Ebola patients.

Sacra's wife said Saturday her husband was "very sick and weak, but slightly improved."

Debbie Sacra visited her husband at the Nebraska hospital where he is receiving treatment along with their son Maxwell, a hospital spokesman told the Associated Press. Taylor Wilson said the family members interacted via a video link for approximately 25 minutes. 

"He asked for something to eat and had a little chicken soup," Debbie Sacra said of her husband in a statement released by the hospital.

Sacra, 51, is the third American to become infected with the virus . He is being treated in 10-bed special isolation unit. The other two, Dr. Kent Brantly and Nancy Writebol, were released from Emory University Hospital in Atlanta last month.

Sacra, a doctor from Worcester, Massachusetts, spent 15 years working at the Liberia hospital where he fell ill. He said he felt compelled to return after hearing that two other missionaries with the North Carolina-based charity SIM with whom he'd worked were sick. He delivered babies at the hospital, and was not involved in the treatment of Ebola patients, so it's unclear how he became infected with the virus.

An estimated 2,100 people have died during the outbreak, but Ebola has not been confirmed as the cause for all of the deaths.

In her statement Saturday, Debbie Sacra thanked the hospital staff and said she said she and her husband were most interested in keeping the focus on the outbreak in West Africa.

"The story is the crisis in West Africa.  That is what is most important," she said. "The world is coming to this fight late."

The Associated Press contributed to this report.