Updated

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 on the seventh floor, the largest of four such units in the U.S.

Sacra, from the Boston area, headed to Liberia after hearing that two other missionaries were sick. He served with the North Carolina-based charity SIM. Sacra delivered babies 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.

Local media reported shortly after 6 a.m. that a plane carrying Sacra landed 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.

The team is discussing experimental treatments, including using blood serum from a patient who has recovered from Ebola, Smith said.

"We've been trying to collect as much information on possible treatments as we can," Smith said.

There are no licensed drugs or vaccines for the disease, but about half a dozen are in development. None has been tested on humans, but an early trial of one vaccine began this week in the United States.

Much attention has focused on the unproven drug ZMapp, which was given to seven patients, two of whom died. But the limited supply is now exhausted and its developer says it will take months to make even a modest amount.

The first two American aid workers infected by Ebola -- Dr. Kent Brantly and Nancy Writebol -- have recovered since being flown to Emory University Hospital in Atlanta for treatment.

Smith and several other doctors with the unit repeatedly said Sacra's transfer to Omaha posed no threat to the public, noting Ebola is transmitted through close contact with an infected person.

He said Sacra was in stable condition in Liberia and was able to board the plane to the U.S. under his own power.

SIM's president, Bruce Johnson, said Sacra had received excellent care in Liberia, but that the Nebraska facility has advanced monitoring equipment and can provide more treatment options.

Sacra's wife, Debbie, said at a news conference at the University of Massachusetts Medical Center in Worcester that her husband was in good spirits as he boarded the plane Thursday. She said the couple had known there was a risk of Ebola infection when he left for Liberia in August.

"I knew he needed to be with the Liberian people," she said. "He was so concerned about the children that were going to die from malaria without hospitalization and the women who had no place to go to deliver their babies by cesarean section. He's not someone who can stand back if there's a need he can take care of."