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The World Health Organisation (WHO) has confirmed two new cases of Ebola in Guinea, ending a two-week spell in which no new infections were reported.

One case was found in the capital Conakry and the other in Forecariah, a town in western Guinea.

The week before last was the first week that the three worst-affected countries - Guinea, Sierra Leone and Liberia - had seen no new infections.

The virus has killed more than 11,000 people in nearly two years.

The case in Forecariah appeared to be linked to a previously known chain of infection, while the one in Conakry seemed to be new, authorities in Guinea said.

"On the bumpy road we keep talking about - the high risk of recurrence - once again we are navigating a few bumps," said WHO spokeswoman Margaret Harris on Friday.

"Of course we didn't want it, but we did expect it. Guinea hadn't got to the stage where we were looking at 42 days".

A country is considered to be Ebola-free after 42 days without a new case.

Liberia recently achieved this status and neighbouring Sierra Leone is nearly halfway through the 42 days.

The enduring risks from the virus were highlighted this week when a British nurse fell "critically ill", 10 months after recovering from Ebola.

A new study has also shown that Ebola persists in the semen of male survivors for up to nine months - much longer than previously thought.