Two U.S. aid workers who contracted Ebola while working in West Africa have been treated with an experimental drug, but it's too early to tell if the treatment is the "magic bullet" to cure them, warns one infectious disease specialist.

Dr. Kent Brantly and Nancy Writebol consented to be treated with the unlicenced drug ZMapp after contracting Ebola in Liberia, even though the drug's safety has never been tested on humans.

ZMapp is made up of three monoclonal antibodies, which target specific parts of the Ebola Zaire virus, the strain of Ebola behind the current outbreak.

The two aid workers are being treated at Emory University Hospital in Atlanta, Ga., and Writebol's husband says her family now has a reason to be "hopeful" for her recovery.

But Dr. Neil Rau, an Ontario-based infectious disease consultant, said that while the drug treatment is "promising," researchers still have to perform controlled trials of the drug with a larger group of patients.

"Although this is a very promising story, having one patient receive it and having a good outcome is not the same as a clinical trial," he told CTV News. "I would be a little cautious about hailing this as the 'magic bullet,' but it's very interesting."

Rau said Brantly and Writebol likely agreed to take the experimental drug because of their situation, which he described as "damned if you do, damned if you don't."

"If you don't give the drug and the patient dies, you say 'Gee, we should have tried, this is a perfectly healthy person who died in the line of duty,'" he said.

"If you do give it and it's actually worsening things or not making things better, you might have a false sense of security or (be making) things worse, and it's unchartered waters until this is studied in a very careful scientific fashion."

Rau warned that until the drug is tested on a larger group of patients, researchers can't rely on the outcomes of a few anecdotal cases.

He also noted that some Ebola patients who received early medical care have improved, even without receiving the drug therapy.

Rau believes that under careful supervision, the drug could potentially be tested in the field on Ebola patients in West Africa who consent to its use.

"If there are enough resources to do trials in Africa, this could be an opportunity to see if this could be a possible treatment, but I don't think we have enough experience yet to be hailing this as a cure," he said.

The current Ebola outbreak has killed close to 900 people and infected at least 1,603 people, according to the World Health Organization.

With a report by CTV News' Medical Correspondent Avis Favaro and Senior Producer Elizabeth St. Philip and files from The Associated Press and The Canadian Press