Kent Brantly, who contracted the deadly Ebola virus, stands with wife Amber during a press conference at Emory University Hospital in Atlanta, Georgia on Thursday.

AFP

Two American missionaries who were sickened with the dangerous Ebola virus while working in Liberia are doing better and have been released from an Atlanta hospital, doctors said on Thursday.

Doctor Kent Brantly, 33, and Nancy Writebol, 60, both Christian aid workers, were infected with Ebola in Monrovia last month as the largest outbreak in history swept West Africa.

They were airlifted to Emory University Hospital for treatment three weeks ago.

"The discharge from the hospital of both these patients poses no public health threat," said Bruce Ribner, director of Emory's Infectious Disease Unit.

"This is a fairly devastating disease, but we would anticipate that in general most patients, if they have not had any substantial organ damage, will make a complete recovery."

Writebol was released on August 19, and did not appear at a press conference with Brantly.

Her release was not announced earlier this week because she had requested privacy and did not want details of her medical condition to be made public, doctors said.

"I am thrilled to be alive, to be well and to be reunited with my family," Brantly said, looking thin but otherwise healthy as he smiled and held hands with his wife.

"I am incredibly thankful to all of those who were involved in my care, from the first day of my illness all the way up to today - the day of my release from Emory."

Franklin Graham, the president of the Christian missionary group for which Brantly worked in Liberia, Samaritan's Purse, hailed the doctor's "courageous spirit" as he battled the virus.

The current outbreak of Ebola virus has killed 1,350 people and sickened more than 2,400 since March in Liberia, Guinea, Sierra Leone and Nigeria.

There is no drug or vaccine for Ebola, which can cause fever, vomiting, diarrhea and fatal organ failure and system-wide haemorrhage.

It is transmitted by close contact with bodily fluids, putting healthcare workers, loved ones and those who kiss or touch bodies during funeral rites at particular risk.

Both American patients were given an experimental treatment called ZMapp, which is made in tobacco leaves and contains a cocktail of antibodies.

However, the drug is in short supply and doctors have stressed they have no way of knowing if it helped the patients recover or not.

The World Health Organisation said two more doctors and one nurse in Liberia have now received ZMapp.

"The nurse and one of the doctors show a marked improvement. The condition of the second doctor is serious but has improved somewhat," said a WHO statement.

Brantly had also received a blood transfusion in Liberia from a boy who had recovered from Ebola virus.

Brantly fell ill on July 23, and his diagnosis with Ebola was confirmed on July 26, he said.

He said he now plans to retreat from the public eye to spend some time with his family.