The World Health Organization said Saturday it could not meet a request from Sierra Leone to take a doctor who contracted the deadly Ebola disease out of the country to seek treatment abroad. 

Dr. Olivet Buck is the fourth doctor from Sierra Leone to come down with Ebola, which has been blamed for 2,400 deaths in West Africa, according to the World Health Organization. Liberia, Sierra Leone and Guinea have recorded the vast majority of cases.

Buck, a citizen of Sierra Leone, would be the first doctor from one of the countries hit hardest by Ebola to receive treatment abroad. The other three doctors from Sierra Leone died in the country.

A letter from President Ernest Bai Koroma's office said he had approved Buck's evacuation to a hospital in Hamburg, Germany, "where they are in readiness to receive her."

The letter, sent to the WHO's country representative on Friday and seen Saturday by The Associated Press, said Buck tested positive for Ebola on Tuesday. "We have been informed that Dr. Buck is quite ill," it said.

A spokesman for the WHO said on Saturday, however, that it could not comply with the request and instead would work to give Buck "the best care possible" in Sierra Leone, including access to experimental drugs.
 
"WHO is unable to organize evacuation of this doctor to (Germany) but is exploring all options on how to ensure best care," WHO spokesman Tarik Jasarevic said. 
 
"WHO will facilitate the best care possible in country for Dr. Buck, including access to experimental drugs," Jasarevic said. 

There is no licensed treatment for Ebola, though a small number of patients have received unproven treatments, with mixed results. It is not clear how these treatments influenced whether the patients recovered or not.

More than 135 health workers have died

Because Ebola is only transmitted through contact with the bodily fluids of people showing symptoms or from dead bodies of Ebola victims, health workers have been especially vulnerable as they respond to the worst outbreak in history.

More than 135 health workers have died so far, exacerbating shortages of doctors and nurses in West African countries already hindered by shortages of health workers.

So far, only foreign aid and health workers have been evacuated abroad for treatment from Sierra Leone and Liberia.

Dr. Sheik Humarr Khan, Sierra Leone's top Ebola doctor, was being considered for evacuation to a European country when he died of the disease in late July.

Cuba's health ministry announced Friday it will send more than 160 health workers to fight Ebola in Sierra Leone, a move that WHO Director-General Dr. Margaret Chan said would "make a significant difference."