(AFP, REUTERS) - Two American missionaries who contracted Ebola while treating patients in Liberia have left hospital after making a full recovery, doctors said on Thursday.

Dr Kent Brantly, 33, and Ms Nancy Writebol, 60, caught the disease in Monrovia in the midst of an outbreak that has killed 1,350 people since March in Guinea, Liberia, Nigeria and Sierra Leone.

The pair were given experimental drugs before being airlifted back to the United States, where they have been treated at a hospital in Atlanta for the last three weeks.

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

Ms Writebol's son Jeremy said on Friday that his mother is still regaining her strength. "She's tired and trying to rest," he told NBC. "There's still some physical recovery that has to go on there. But her colour's good and strong. She seems pretty happy."

Speaking alongside his brother Brian, he said the family has experienced "the lowest of lows and at the same time the highest of highs" since Ms Writebol contracted the Ebola virus in July while working for a Christian mission organisation in Liberia, grappling first with her potential death and later her recovery.

He said faith, the care at Emory and the experimental drug ZMapp likely helped her survive the virus, which has a low survival rate. Ebola can kill up to 90 per cent of those who become infected, although the fatality rate in the current epidemic is about 60 per cent.

Nancy's husband, David, had been in quarantine after returning from Africa but the two have since reunited.

Mr Jeremy Writebol has said the couple has not ruled out returning to their Christian mission work in West Africa. "She still thinking about it," he told NBC. "Africa's still in their heart and the suffering of the people in western Africa is still very deep for them."