Nathaniel Blama, the head of the Environmental Protection Agency, tested positive on Monday morning. He returned from Switzerland on Friday.

The announcement was made on state-run radio by Information Minister Eugene Nagbe. It has sparked panic in the capital, Monrovia, despite the minister's assurance that measures are in place to control the spread of the virus.

The authorities say they have intensified efforts to trace all people who may have been in contact with the patient.