OMAHA, Neb. — A doctor who became infected with Ebola while working in Liberia — the third American aid worker sickened with the virus — arrived Friday at a Nebraska hospital for treatment.

Officials at the Nebraska Medical Center in Omaha have said Dr. Rick Sacra, 51, will be treated at the hospital’s 10-bed special isolation unit, the largest of four such units in the U.S.

Sacra, a doctor from suburban Boston who spent 15 years working at the Liberia hospital where he fell ill, felt compelled to return after hearing that two other missionaries were sick. Sacra delivered babies at the hospital, but was not involved in the treatment of Ebola patients, so it’s unclear how he became infected with the virus that has killed about 1,900 people.

The plane carrying Sacra landed shortly after 6 a.m. Friday at Offutt Air Force Base, south of the Omaha suburb of Bellevue. He arrived at the hospital in an ambulance about 40 minutes later, but media were unable to see Sacra as he was hustled into the facility.

Dr. Phil Smith, medical director of the Omaha unit, said a team of 35 doctors, nurses and other medical staffers will provide Sacra with basic care, including ensuring he is hydrated and keeping his vital signs stable.