OMAHA, Neb. (AP) — The Nebraska doctors treating the man who became infected with Ebola while working in Liberia say he is making progress, but it’s not yet clear if he will recover.

Dr. Rick Sacra arrived at the Nebraska Medical Center on Friday for treatment in the hospital’s specialized 10-bed isolation unit. Two of the doctors treating him gave an update on his condition Sunday.

Dr. Phil Smith says Sacra remains very tired, but his progress has been encouraging.

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

Smith says Sacra has even made a few jokes with the doctors treating him.

The 51-year-old Sacra is the third American aid worker to be sickened with the Ebola virus.