A U.S. doctor who contracted Ebola while working in Africa in the 1970s says his eventual recovery was a slow and lengthy process that took several months.

Dr. Tom Cairns contracted Ebola in 1972 – four years before it was first discovered by researchers in 1976 -- while working at a hospital in Zaire, the country which eventually became part of the Democratic Republic of the Congo.

Cairns said he came down with the virus after a patient who was almost "dead on arrival" came into the hospital. The patient died several minutes later and authorities later ordered an autopsy, which was performed by Cairns.

"In doing the autopsy, I stuck my finger with the scalpel and 12 days later I came down with what was a very, very severe infection (and) flu-like symptoms," on Tuesday.

Cairns, who now lives in Bloomington, Minn., described the infection as "the worst kind of flu you can imagine," with symptoms including headaches, vomiting, diarrhea and "aching all over."

He said he doesn't remember much from the first few days after he contracted the virus.

"The recovery was very slow, it was two full weeks before I really even remembered anything," , noting that most of what he knows about those initial days was told to him by his wife and colleagues.

He said it took six weeks before he was able to partially return to work at the hospital, and several months before he started to regain his strength.

Donating blood to research

After recovering, Cairns donated blood to researchers studying the virus. However, he doubts that his blood and antibody samples are being used in the current research on the experimental Ebola treatment ZMapp.

Antibodies are proteins that circulate in the bloodstream and are used by the body's immune system to fight bacteria and viruses.

Cairns said that by the third time he donated blood, researchers told him that his antibody levels were so low that they wouldn't be able to use his blood for much longer.

"I know that if I were to go back into the Ebola crisis again, working with patients, and if I were exposed, I would quickly generate antibody again," he said. "But at least at this point, I probably don't have much left."

Earlier on Tuesday, American aid worker Nancy Writebol at Emory University Hospital in Atlanta, after being treated with ZMapp. Writebol had been working in the west-African nation of Liberia.

Another American infected with Ebola, Dr. Kent Brantly, is also being treated at Emory.

Both Brantly and Writebol agreed to be treated with ZMapp after contracting the virus while treating Ebola patients at a Liberian missionary clinic.

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

With files from The Associated Press and The Canadian Press