NAIROBI — Just one week after an outbreak of the Ebola virus was extinguished in northwestern Congo, a new one was declared in the country’s conflict-hit northeast. This is Congo’s 10th Ebola outbreak since the 1970s, and some health officials are worried it might be the hardest to contain.

The new outbreak is centered on a thickly populated stretch of Congo’s eastern border with Uganda — an area that is also the epicenter of decades-long clashes between dozens of militias that have forced millions into squalid refu­gee camps.

At least 43 people are believed to have been infected in North Kivu province, including 36 who have died, Congo’s health ministry said on Tuesday. Sixteen of the cases were confirmed to be Ebola.

While Congo has experienced the most outbreaks of the Ebola virus, this is the first time it has cropped up in this part of the country. Lab tests have confirmed it is the same strain as the previous outbreak, which started in early May, but there is no indication the outbreaks are related.

“We are still in the early days, and there are lots of unanswered questions,” said Peter Salama, the World Health Organization’s head of emergency response. “But we are expecting this one to be significantly more costly and complex than the last.”

There are already 25 suspected cases in the city of Beni, a center for displaced people and home to 350,000. There are also two probable cases in Butembo, a city of nearly 1 million and a key trading hub between Congo and Uganda.

As in most past outbreaks — including the vast epidemic that swept Liberia, Sierra Leone and Guinea between 2014 and 2016, killing more than 11,000 people — this one probably began to spread quickly when one of the initial cases died and was buried by family members who were unaware that touching the deceased’s body would infect them. Salama said WHO had identified seven family members of a 65-year-old woman who was given an “unsecured burial.” All seven contracted the virus.

Ebola lives in what health officials call the “animal reservoir” — meaning it can be contracted only by being bitten by an infected animal (most commonly bats and monkeys), by handling an infected animal or by eating the meat of one. Some Congolese diets include wild animals, among them bats and monkeys, commonly referred to as bushmeat.

The outbreak that started in May was confined to Equateur province, along the heavily trafficked Congo and Ruki rivers, and killed 33 people.

The virus was briefly present in the regional trading hub of Mbandaka, raising fears it could travel rapidly to other population centers or spread within the city, but rigorous tracing of possible cases by Congo’s health ministry, WHO, and other public health organizations prevented those worst-case scenarios.

“All the factors that made the Equateur outbreak enormously complex are present in the new one in North Kivu,” Salama said. “Urban centers, infected health-care workers, proximity to international borders — it’s all there. But then you have 20 highly active militias in the region as well, and more than a million displaced by them.”

The conflict makes one essential component in preventing Ebola’s spread particularly difficult: tracing the contacts of those who are suspected to be infected. There are numerous areas of North Kivu and neighboring Ituri provinces that are highly volatile and often cut off entirely by clashes.

Salama told reporters at a news conference earlier this week health workers may need armed escorts when they trace contacts.

“Beni is more or less surrounded by armed groups,” said Nicolas Lambert, the deputy leader of the International Committee of the Red Cross in Congo, who is in Beni. “We have an ongoing dialogue with several of them to negotiate the safety of our health workers. But, more importantly, we must all work to stop the outbreak before it becomes lodged in areas with more active fighting.”

According to the Reuters news agency, authorities in North Kivu announced on Tuesday 14 bodies had been discovered in the town of Tubameme, about 25 miles northeast of the outbreak’s epicenter. The various conflicts in North Kivu and Ituri are led by both ethnic and religious armed militias, and the government, based more than 1,000 miles away in Kinshasa, exerts only sporadic control.

But the conflict does make the response to the outbreak easier in one way.

The region is home to the world’s largest and most expensive peacekeeping operation, a United Nations mission known as MONUSCO. It has contributed to the building of roads and airstrips, which will make the delivery of supplies somewhat easier than in Equateur, which has the least developed infrastructure in what is already one of the world’s least developed countries.

Experimental vaccines that were successfully deployed in Equateur are being delivered to the area around Beni. More than 3,000 were left over in Congo from the last outbreak, and a WHO spokesman told reporters in Geneva on Tuesday vaccinations of health-care workers in North Kivu would start on Wednesday.

The vaccines are made by the pharmaceutical giant Merck, and 300,000 more could be provided on short notice.