Democratic Republic of Congo has recorded its first death from Ebola in the eastern trading hub of Butembo, a city of almost a million with links to Uganda that could complicate efforts to control the outbreak, health officials said on Wednesday.

The epidemic is believed to have killed 85 people since July and infected another 39. Most have been in villages but about 20 cases have been in Beni, a city of several hundred thousand people with close links to Uganda.

Butembo, about 55 km (35 miles) away, is two or three times the size of Beni. It straddles a major trading route for consumer goods entering Congo from East Africa and for Congolese exports of artisanal gold, coltan, timber and other materials to East African ports via Uganda.

“Ebola case from Beni has died in Butembo DRC,” Peter Salama, the World Health Organization’s head of emergency operations, wrote on Twitter.

“Good news is case detected quickly, response already in place and expanding. Bad new(s) is increases risk of further spread, and having Ebola in an urban center makes ending the outbreak much harder,” he said.

Butembo’s mayor Sylvain Kanyamanda said the victim was a woman who was likely infected as a result of participating in an unsafe burial. She died in a university clinic.

“We call on the population to exercise caution and to respect all hygiene measures recommended by health workers,” he said.

Health officials say they have made progress slowing the virus’s spread with experimental vaccines and treatments. But they cannot be sure the situation is under control due to difficulties accessing some areas.

Two South African peacekeepers were wounded in a rebel ambush near the epicenter of an Ebola outbreak in eastern Democratic Republic of Congo, their U.N. mission said on Tuesday.

Congo has experienced 10 outbreaks of Ebola since it was discovered in the country’s forested north in 1976. The disease causes hemorrhagic fever and kills about half of the people it infects.