MONROVIA, Liberia (AP) — One of Liberia’s most high-profile doctors has died of Ebola, officials said Sunday, and an American physician was being treated for the deadly virus, highlighting the risks facing health workers trying to combat an outbreak that has killed more than 670 people in West Africa — the largest ever recorded.

A second American, a missionary working in the Liberian capital, was also taken ill and was being treated in isolation there, said the pastor of a North Carolina church that sponsored her work.