The death toll from an outbreak of the Ebola virus in the Djera region of northern Democratic Republic of Congo has risen to 31, Minister of Health Felix Kabange Numbi told Reuters on Tuesday.

The outbreak in Congo's Equateur province is thought to be separate from an epidemic in the West African nations of Guinea, Sierra Leone and Liberia that has killed more than 1,550 people since March. 

On Monday, Nigeria has confirmed case of Ebola disease in the oil hub of Port Harcourt, bringing the country's total confirmed infections to 16, with around 200 people under surveillance, the health minister said.

A doctor in Port Harcourt died last week after treating a contact of the Liberian-American man who was the first recorded case of the virus in Africa's most populous country. That raised alarm that Ebola, which looked on the verge of being contained in the commercial capital, Lagos, may flare up again elsewhere.

Patrick Sawyer, the first case, came in from Liberia, then collapsed at Lagos airport on July 20.

The shift to Port Harcourt shows how easily containment efforts can be undermined. Nigeria's government acted quickly at the end of July, setting up an isolation ward and monitoring contacts closely. But one of Sawyer's contacts in Lagos avoided quarantine and traveled east to Port Harcourt.

He has since recovered from the disease, but he infected the doctor who treated him, who then himself died of Ebola. A third case in the oil city was a female patient in the same hospital as the doctor and caught the disease from him.

Health Minister Onyebuchi Chukwu said in a press conference that 72 people in Lagos, a city of 21 million people, were still under surveillance.

"Two other contacts of the late Port Harcourt doctor, one of the doctors who managed him and a pharmacy technician working in the doctor's hospital, are symptomatic and have been admitted to the isolation ward in Rivers," Chukwu said, although he added that preliminary tests had been negative for Ebola.

The outbreak of Ebola in West Africa is the world's worst ever. It has killed at least 1,550 people, and the World Health Organisation says it could infect 20,000 more.

Reuters