The year-long Ebola outbreak in the Democratic Republic of the Congo has spread to a new province, with two cases – one of them fatal – confirmed in South Kivu.

The confirmed cases were reported in the Mwenga area, some way south of the city of Bukavu, which sits on the country’s eastern border with Rwanda.

The latest cases, which have been concentrated around the cities of Beni and Butembo, follow recent deaths from the disease in the major city of Goma.

The Ebola outbreak in eastern DRC has killed 1,808 people out of 2,765 confirmed cases, according to the ministry of health. The current outbreak, which started in August last year, is the second largest in history.

One of the two new cases was a 24-year-old woman who had already had been identified last month as a high-risk contact of another Ebola case in Beni, more than 700km north, according to a government statement issued on Friday.

She travelled by bus, boat and road with her two children to Mwenga, in South Kivu, where she died on Tuesday night, according to a slide from a presentation by health officials.

Most of the cases reported outside the area of the immediate outbreak, including across the border in Uganda, have involved patients who have travelled from the area at the centre of the outbreak in North Kivu.

“Two cases which tested positive for Ebola were confirmed overnight in South Kivu, in Lwindi district in the Mwenga region,” the health ministry said in a statement.

The new cases are “a 24-year-old woman and her seven-month-old child,” said Dr Jean-Jacques Muyembe, the director of DRC’s National Institute for Biomedical Research, in a statement released on Friday. The child is being treated.

The woman had received the experimental vaccine that has been used widely to inoculate contacts. However, the vaccine is not infallible, although it is believed to protect about 97% of those who have received it.

The new cases will again raise serious questions about whether the large-scale, international-led health response to the Congolese Ebola crisis is capable of containing the outbreak, which has been described by some officials as the most complex public health emergency in history.

In July, the outbreak was declared a public health emergency of international concern, but cases have nonetheless continued to appear in new locations amid acknowledged problems tracking contacts of those contracting the disease.

Dr Tedros Adhanom Ghebreyesus,the WHO director-general, tweeted: “Sad to confirm that two people who travelled from Beni to Mwanga in South Kivu, #DRC are infected with #Ebola. This has sparked a rapid response … to provide treatment, identify all contacts, raise community awareness and begin vaccinating.”

According to officials on the ground, a team was sent by air from Goma – the region’s largest city and home to nearly 2 million people – to Mwenga on Friday to assist with the response.

Ebola treatment centres have repeatedly been attacked by armed militiamen and disgruntled locals, hampering efforts to contain the epidemic in the conflict-ravaged east.