Ebola survivor Dr. Kent Brantly donated a unit of blood to treat the third American aid worker infected with the virus as doctors fight to save the patient’s life, Samaritan’s Purse tells NBC News. Brantly flew to Nebraska last week to donate his blood to use to treat Dr. Rick Sacra, Samaritan's Purse President and CEO Franklin Graham said. "He flew out from North Carolina to Nebraska to give a unit of blood," Graham said in an interview with NBC News. "His blood was a perfect match."

Sacra, a volunteer who was working in Liberia for another group, SIM, is being treated at the Nebraska Medical Center in Omaha.

"It really meant a lot to us that he was willing to give that donation so soon after his own recovery," Sacra's wife, Debbie Sacra, told a news conference. She spoke to Brantly's wife, Amber. "We both marveled at the fact that they had the same blood type."

Sacra also has received an experimental drug, but his doctors say they have been asked not to say which drug.

Using serum from the survivor of a disease is not a new approach, but it's considered highly experimental. Last week the World Health Organization endorsed the approach, saying it was worth trying. The idea is that survivors have antibodies to the virus in their blood, and those antibodies can kick-start the immune system of another patient.

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Graham thinks it helped. "Dr. Brantly said that when he saw him last week he was in pretty bad shape," Graham said. "It sounds like he has made a dramatic turn." Sacra was reported up and joking as he underwent treatment at Nebraska's special biocontainment unit.

"His progress has been remarkable," Dr. Angela Hewlett, who is treating Sacra, told a news conference.

Brantly and fellow missionary Nancy Writebol were treated at Emory University Hospital in Atlanta. They both got an experiment therapy based on engineered antibodies called ZMapp, and Brantly also got a unit of blood from an Ebola survivor. "Dr. Brantly is now immune to that strain of Ebola," Graham said.

Doctor say they'll never know what precisely led to their recovery, but they say the specialized care given in a modern U.S. hospital has to have been a major factor. They say Ebola patients lose not only fluids through near constant diarrhea and vomiting, but they also lose important minerals such as potassium and magnesium that are key for healthy organ function -- especially the heart.

Graham said Brantly made the flight to and from Omaha on a Samaritan's Purse plane. "He wanted to keep it quiet because he doesn't want anyone to believe he is a hero," Graham said.

“I would be willing to do anything I could to help my friend," Brantly said through a Samaritan's Purse spokesman.

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#NebraskaMedEbola patient Dr. Rick Sacra continues to improve. His wife, Debbie, read the Bible to him today. pic.twitter.com/ATwTIUdf1E — Nebraska Med Center (@NebraskaMed) September 10, 2014

Ebola-Stricken Doctor Gaining Energy and Making Jokes http://t.co/23phBrDJTb — NBC News Health (@NBCNewsHealth) September 7, 2014

— Maggie Fox