The eastern DR Congo province of South Kivu said Friday it had recorded its first confirmed cases of Ebola in the country's year-old epidemic, one of which was a fatality.
The new cases revived concern that the virus could cross the porous borders of the central African country, where it has claimed more than 1,900 lives since August last year.
"Two cases which tested positive for Ebola were confirmed overnight in South Kivu, in Lwindi district in the Mwenga region," the provincial government said in a statement.
"A 26-year-old victim died and (one of their) children who tested positive is still alive and being treated."
South Kivu Governor Theo Ngwabidje told reporters: "Teams from the national anti-Ebola coordination campaign arrived yesterday to provide support."
World Health Organization (WHO) chief Tedros Adhanom Ghebreyesus tweeted the outbreak in South Kivu "has sparked a rapid response... to provide treatment, identify all contacts, raise community awareness & begin vaccinating".
The International Federation of Red Cross and Red Crescent Societies (IFRC) said it was "rapidly deploying an expert team" to the area.
Risk of crossing border 'enormous'
The haemorrhagic virus erupted in the Democratic Republic of Congo's North Kivu province on August 1, 2018 and spread to neighbouring Ituri province.
The UN's World Health Organization (WHO) declared the epidemic a "public health emergency of international concern" last month after cases were confirmed in the densely-populated North Kivu capital city Goma.
The city's proximity to Rwanda and many transport links sparked fears the disease could spread across borders.
"Beni, Butembo and Goma are still containable," said a Congolese professor and epidemiologist, referring to North Kivu cities.
"But with the disease in South Kivu, the risks of it spreading to (the eastern DRC town) of Kalemie, Tanzania and Burundi are enormous."
Residents in South Kivu's capital Bukavu said they were concerned.
"At this time of year, we rarely have running water -- how are we going to avoid this disease if we have to frequently wash our hands?" asked mother-of-five Martine Mushagalusa.
Anselme Kangeta, a 35-year-old man, said: "Given the crowded way we live, movement is uncontrolled, people go from one place to another without taking precautions. The authorities must get involved otherwise we will all die."
South Kivu had experienced a Ebola scare on July 31 when doctors briefly quarantined 15 people in the town of Birava over fears they were infected, but tests came back negative.
Ebola is named after a river in northern DRC, then named Zaire, where the virus was first identified in 1976 by a Belgian-led scientific team.
The pathogen causes fever, vomiting and severe diarrhoea, often followed by kidney and liver failure, internal and external bleeding.
The disease is spread by contact with infected bodily fluids and is fought with time-honoured but laborious techniques of tracing contacts and quarantining them.
The outbreak is the second deadliest on record after more than 11,000 people were killed in Guinea, Sierra Leone and Liberia between 2014-2016.
The cases in South Kivu come on the heels of an announcement of a breakthrough in the quest for drug to treat Ebola.
US researchers on Monday said two prototype drugs, known by their lab names as REGN-EB3 and mAb114, slashed mortality rates among Ebola patients in a trial in eastern DRC.
The authorities have also deployed a US-made vaccine called rVSV-ZEBOV, which is unlicensed but has been widely tested for safety, to protect health workers in the campaign against Ebola.
DR Congo's pointman on Ebola, Jean-Jacques Muyembe, on Thursday predicted that because of the new drugs, as well as the vaccine, "we can manage to completely control the epidemic in three to four months".
Nearly 200,000 people have received the jab so far.
Burundi on Wednesday said it had begun immunising frontline workers with the vaccine at its border with DRC.