(CNN) The Ebola virus outbreak in the Democratic Republic of Congo has killed 33 people, the World Health Organization said Sunday.

An additional 43 suspected cases of Ebola were reported, including 13 confirmed by lab testing, according to WHO.

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The outbreak is spreading through five health zones in North Kivu province and one health zone in Ituri province, which poses geographic and political challenges, the WHO said. North Kivu borders Rwanda and Uganda and trade activity fuels heavy movement across the borders.

North Kivu also hosts over 1 million displaced people and fighting between government forces and armed militant groups makes containing the highly infectious virus a challenge.

"We're responding to an outbreak of this high-threat pathogen, with one of the highest mortality rates of any known disease, but in the context of a war zone," Peter Salama, Head of Emergencies at WHO said.

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