Ebola has killed more than 350 health workers in West Africa, depleting the ranks of doctors and nurses in countries that already had too few to begin with.
Because Ebola is spread through bodily fluids, it is only transmitted through close contact.
It is often called the "caregivers' disease" because those infected are typically family members caring for the sick or health workers treating them.
Dr Victor Willoughby tested positive for Ebola on Saturday and was being treated at a clinic near the capital run by the medical charity Emergency, said Dr Brima Kargbo, the country's chief medical officer.
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The 67-year-old died this morning, just hours after an experimental drug arrived in the country for him. The arrival of ZMAb, developed in Canada, had raised hopes for Willoughby's survival.
But he died before a dose could be administered, said Kargbo. ZMAb is related to ZMapp, another experimental drug that has been used to treat some Ebola patients.
The drugs' efficacy in treating Ebola has not yet been proven.
Ebola has sickened more than 18,600 people, the vast majority in Sierra Leone, Guinea and Liberia. Of those, more than 6,900 have died.
The infection rate in Liberia has been declining, while it is fluctuating in Guinea.