One of Sierra Leone’s leading Ebola doctors has died from the disease, making him the fifth high-profile local doctor killed by the virus. Dr. Godfrey George, medical superintendent of Kambia Government Hospital in northern Sierra Leone, died Monday at a hospital in Freetown, the country’s capital city, according to the Associated Press. Authorities said his death marked a blow to efforts to keep health workers treating Ebola patients from contracting the deadly infection that has killed nearly 5,000 people across West Africa since March.

Dr. George was taken to Freetown over the weekend after he reported feeling ill. He tested positive for Ebola on Sunday. Health workers have been particularly vulnerable to Ebola and continue to die at higher rates than the general population because of their proximity to the body fluids of infected patients.

Since the outbreak in West Africa began, a total of 523 health care workers have become infected with Ebola, according to the World Health Organization’s latest estimates. Over half of them have died. “Ebola has taken the lives of prominent doctors in Sierra Leone and Liberia, depriving these countries not only of experienced and dedicated medical care but also of inspiring national heroes,” the WHO said in August.

Meanwhile, a U.N. employee who had been working in Sierra Leone was being treated Monday at a hospital in Paris, the French government announced Saturday. The employee, who has not been identified, was evacuated from West Africa and was in “high-security isolation,” the AP reported.

There have been a total of 13,567 confirmed or suspected cases of Ebola as of Oct. 31. The number of deaths has reached 4,951, according to the WHO. Liberia has had the most cases of Ebola, followed by Sierra Leone and Guinea. Nigeria’s outbreak ended Oct. 20. Mali and Senegal have reported just one case each of Ebola.