DAKAR, Senegal (AP) — Health workers are scrambling to trace those who may have been exposed to a man who died Friday from Ebola, one of the deadliest diseases known to man.

No one knows for sure just how many people Patrick Sawyer came into contact with the day he boarded a flight in Liberia, had a stopover in Ghana, changed planes in Togo, and then arrived in Nigeria.

An Ebola outbreak that emerged in March has killed more than 670 people in Guinea, Sierra Leone and Liberia.

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