Ebola is back in Congo. This time it may be harder to fight.

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The Ebola virus has popped up again in the Democratic Republic of Congo, days after another outbreak was declared over — but this time it may be harder to fight.

The new outbreak is across the vast Central African nation from the last one, 1,500 miles away and in an area disrupted by conflict and teeming with refugees, aid workers say. It will be difficult and dangerous to track down cases to isolate and treat them.

“Here we are responding to an outbreak of a high-threat pathogen … in the context of a war zone,” Peter Salama, deputy director-general of emergency preparedness for the World Health Organization, said at a news conference in Geneva Friday.

“In terms of difficulty scales, we are at the top of the difficulty scale.”