Health officials on Tuesday warned that the Ebola outbreak in East Africa could significantly worsen, saying that the virus could last as long as a year and infect thousands of people if current transmission rates go on unabated.

The outbreak is already one of the largest on record, and has spread most in the Democratic Republic of Congo, where distrust of the authorities and violence in eastern regions have hampered health workers’ ability to help people.

“If we don’t stop the outbreak very soon it will be worse than what we had in West Africa and eastern D.R.C.,” said Jean Kaseya, the director general of the Africa C.D.C., said on Tuesday at an emergency conference on Ebola for African leaders.

There have been more than 800 confirmed cases in this outbreak, according to the Africa Centres for Disease Control and Prevention, and nearly 200 people killed. The worst recorded Ebola outbreak took place between 2014 and 2016 in West Africa and killed more than 11,000 people, according to the World Health Organization.

Dr. Kaseya’s remarks were echoed by other health officials and experts, who warned that health workers were already facing steep obstacles.

“We are running after the disease,” said Bruno Michon, who is managing the Ebola response in Congo for the International Federation of Red Cross and Red Crescent Societies.

Mr. Michon said in a phone interview Tuesday that the outbreak would take months to contain, and potentially as long as a year if infection rates continue to rise. The disease has spread across the border from Congo into Uganda.

Officials said they were particularly concerned about this outbreak because it was spreading in an area where stigma and misinformation have pushed people away from treatment centers, and where public health measures have clashed with traditional burial practices.

African leaders have appealed for sustained help in combating the outbreak, including at the conference on Tuesday. “Delayed action can transform a localized outbreak into a regional and a global crisis,” President Cyril Ramaphosa told other leaders. “That is why our response must focus on breaking the transmission and stopping Ebola at its source.”

At the Group of 7 summit in France on Tuesday, leaders of the world’s wealthiest nations issued a joint statement calling for a “coordinated response” to contain the outbreak and provide humanitarian assistance.

Officials warn that current estimates of cases may significantly undercount the true toll.

Bundibugyo, the type of Ebola virus behind this outbreak, has no targeted vaccine or treatment available yet. Early surveillance and testing failed to identify it, delaying the response, experts say. Fighting among armed groups and military forces in eastern Congo has displaced millions of people, making it even harder to trace.

Ebola can cause organ failure and internal bleeding, according to the WH.O. It spreads when people come into contact with the blood or other bodily fluids of infected individuals.

“The situation is further complicated by rumors,” said Alex Lock, a communications coordinator with I.F.R.C. based in Bunia, a city where the virus has spread. He said the organization has mobilized hundreds of volunteers to speak with community members door-to-door, urging people to seek medical help if they develop symptoms.

“People don’t want to go to the hospital,” Mr. Lock said, because many believe the disease is “injected” into patients in treatment wards set up by foreign aid organizations.

Funeral practices, health workers said, have also become a major point of friction between residents, who are accustomed to seeing and touching the bodies of loved ones before burial, and officials, who warn that contact with infected bodies can transmit the disease.

Following outrage from residents in affected communities seeking to carry out traditional burial practices, Mr. Michon said, his aid group has started using body bags with windows, “so that families can see the face of the deceased and begin the process of grieving.”

Despite efforts to build community trust, Mr. Michon said affected communities are experiencing “a mix of fear and pain.”

Still, he said, the group’s volunteers have faced fewer attacks in recent weeks from residents who are suspicious of their activities, and he is hopeful that the organization’s messaging will spread awareness.