OMAHA, Neb. -- The third American aid worker who contracted Ebola in Africa was released Thursday from a Nebraska hospital.

An elated Dr. Rick Sacra said at a news conference that the federal Centers for Disease Control and Prevention had cleared him of the Ebola virus. He left the isolation unit at the Nebraska Medical Center on Thursday morning.

"I feel great, except that I am extremely weak," Sacra said.

The 51-year-old doctor from Worcester, Massachusetts, will likely return to Africa someday to help, but he said he expects a long recovery ahead based on what his friend and fellow Ebola survivor Dr. Kent Brantly told him.

"I never felt like I was not going to make it. The care was so excellent, so speedy and so prompt," said Sacra, who contracted Ebola while working at a hospital in Liberia with the North Carolina-based charity SIM and arrived in Omaha on Sept. 5.

The World Health Organization says the Ebola virus is believed to have killed more than 2,900 people in West Africa. Sacra said he's not sure exactly when he became infected with the virus, but he was taking care of very sick pregnant women and delivering babies, including performing several cesarean sections.

"Unfortunately, what we discovered is this epidemic is so widespread and the numbers are so high that sometimes people who don't have the classic symptoms that you're looking for -- that the WHO was training us on -- sometimes those people have Ebola," Sacra said.

Governments are scrambling to contain the disease outbreak, and the United States has promised to send 3,000 soldiers to the region to help. Sacra added that the "odds I'll end up back (in Liberia) are pretty high."

Debbie Sacra spent most of the news conference watching her husband of 29 years instead of the room full of reporters and hospital workers. The two shared their first hug in roughly two months Thursday morning. "It was great to get a hug," she said.

The Sacras planned to return home to Massachusetts soon, but they declined to discuss their exact travel plans. Rick Sacra said he was looking forward to taking his dog for a long walk, but Debbie said more rest would be in order.

Two other American aid workers who contracted Ebola -- including Brantly -- were treated at Emory University Hospital in Atlanta, and were released after recovering. A fourth American with Ebola is still being treated in Atlanta.

Dr. Phil Smith has said Sacra received an experimental Tekmira Pharmaceuticals drug called TKM-Ebola for a week after he arrived in Omaha, as well as two blood transfusions from Brantly. The transfusions are believed to help a patient fight off the Ebola virus because the survivor's blood carries antibodies for the disease.

Sacra also received supportive care including IV fluids and aggressive electrolyte management, and his own immune system fought the virus.

Doctors have said that the combination of treatments Sacra received makes it difficult to know what helped him fight off Ebola. But they noted Thursday that they've been sharing lessons from his case with organizations responding to the outbreak, especially the potential benefits of early IV fluids.