BETHESDA, Md. – An American health worker who contracted Ebola while volunteering in Africa will be admitted to a hospital at the National Institutes of Health, the agency announced Thursday.

The patient was expected to arrive Friday at the NIH research hospital in Bethesda after being transported to the United States in isolation on a chartered plane. The patient’s name, age and gender have not been released.

The patient had been volunteering at an Ebola treatment centre in Sierra Leone. The NIH did not release any further details about the patient.

The agency has one of the few specialized isolation units nationwide. Previously, an American nurse was treated there after she contracted Ebola while caring for a Liberian man who died at a Dallas hospital. The nurse, Nina Pham, survived and is Ebola-free.

The treatment facility at the NIH is staffed by specialists in infectious disease and critical care and is designed to prevent the spread of highly contagious viruses, including Ebola.

The patient will be the 11th person with Ebola to be treated in the U.S., which has more than 50 hospitals designated as Ebola treatment centres.

The World Health Organization estimated Thursday that the virus has killed more than 10,000 people, mostly in the West African nations of Guinea, Liberia and Sierra Leone. The current outbreak is the largest ever for the disease. While deaths have slowed dramatically in recent months, the virus appears stubbornly entrenched in parts of Guinea and Sierra Leone.