The condition of Dr Kent Brantly is improving though he is still not out of danger, according to doctors at the Emory University Hospital in Atlanta.

Kent Brantly, 33, an American doctor who contracted Ebola when treating patients in Liberia, is now a recipient of a controversial therapy called immune plasma infusion where the blood from a survivor is injected into the patient.

A 14-year-old male Ebola patient who had been under Brantly's care, and survived, donated a unit of blood to Brantly, according to Samaritan's Purse President Franklin Graham.

The blood (or plasma, to be medically specific) of a survivor is full of antibodies that can fight the disease might help the patient become immune itself.

During the 1995 Ebola outbreak, seven of the eight who were given blood transfusions from survivors had survived. This method has been used with other infections too. But it has proved difficult with Ebola as it kills fast and the numbers of patients are relatively lesser than with other infections.

Experts are divided on whether the present outbreak is a good time to start collecting plasma.

Meanwhile, commenting on the spread of the disease, Tom Frieden, the director of the Atlanta-based Centers for Disease Control, said: "We can stop it from spreading in hospitals and we can stop it in Africa... in fact, we have stopped every previous outbreak, and I'm confident we can stop this one.

"But it's going to be hard because it's spread through so many countries and there's such a risk of further spread in Africa."