A third U.S. missionary worker who was infected with Ebola in Liberia and flown to the United States for medical care was treated with blood transfusions from another American who recovered from the virus last month.

Dr. Rick Sacra, 51, was admitted to the Nebraska Medical Center in Omaha on Sept. 5. A day later, he got the first of two blood plasma transfusions from Kent Brantly, the 33-year-old missionary doctor released from Emory University Hospital in Atlanta last month after being evacuated from Africa and successfully treated for the deadly disease.

Sacra was infected while delivering babies in Monrovia, Liberia, on behalf of the Christian missionary group SIM USA. He also has been receiving an experimental drug for the past several days, said Angela Hewlett, associate medical director of the hospital's biocontainment unit. Doctors hope the virus-fighting antibodies in Brantly's blood help Sacra.

"We're hoping it jump-starts his immunity," Phil Smith, medical director of the biocontainment unit, said during a conference call with reporters. "To survive you have to build up enough antibodies to neutralize the virus. We're hoping to buy him some time, in other words to give him antibodies to help his immune system battle the Ebola virus and let him get ahead of the curve."

Sacra is stronger and getting back to normal, Hewlett said. He's in good condition and a relapse is less likely, though it's impossible to know for sure, she said.

"We're on new ground here," she said. "There is no way to tell, but I can tell you his progress has been remarkable," she said.

The World Health Organization is encouraging the use of blood taken from Ebola survivors to treat current patients and said last week it should be a priority. The agency is helping establish a system that can be used to safely draw blood from those who have recovered from the disease, prepare it and reinject it into patients. Doctors are also working on lists of survivors by blood type who could donate.