A surge in new cases of Ebola in Liberia has seen the number of people believed to be infected pass 4,200, according to World Health Organisation figures.

Health officials are monitoring more than 200 people in the southern Nigerian city of Port Harcourt who may have been exposed to Ebola after a single man infected a doctor who then continued to treat patients before he himself died of the disease.

The hospital in Liberia where three American aid workers contracted Ebola has been overwhelmed by a surge in patients, a missionary couple have said.