Kinshasa, 19 May 

The World Health Organisation director-general openly worried Tuesday over the “scale and speed” of an outbreak of a rare Ebola variant in eastern Congo, where authorities reported a sharp increase in suspected deaths to at least 131 and over 500 suspected cases.

The virus spread undetected for weeks after the first known death as authorities tested for a more common strain and came up negative, health experts and aid workers said. This Bundibugyo virus, a rare variant, has no approved medicines or vaccines.

Congo's health minister, Samuel Roger Kamba, said investigations were underway to determine whether the deaths and 513 suspected cases were "actually linked to the disease.”

WHO director-general Tedros Adhanom Ghebreyesus said he is “deeply concerned about the scale and speed of the epidemic," adding the UN health agency will convene its emergency committee later Tuesday. He pointed to the emergence of cases in urban areas, the deaths of healthcare workers and significant population movement.

Patient zero has not yet been confirmed

The WHO has declared the Ebola outbreak a public health emergency of international concern, requiring a coordinated response. Resources were being rushed to the two affected provinces near the border with Uganda, which has reported one death in a person who travelled from Congo.

The head of the WHO team in Congo said authorities haven't identified “patient zero” in the outbreak.

Dr Anne Ancia also said the Erbevo vaccine, used against a different Ebola strain, was among those being considered for possible use. But even if that or another is approved, it would take two months to become available.

Inside Congo, cases have been confirmed in the capital of Ituri province, Bunia; North Kivu's rebel-held capital, Goma; and the localities of Mongbwalu, Nyakunde and Butembo — home to well over a million people in all.

Dr Peter Stafford, an American doctor, is among the Bunia cases, said the Christian organisation he works for, Serge. He had been treating patients at a hospital. Three other Serge employees were working there, including Stafford's wife, but were not showing symptoms.

False negative Ebola tests delayed the response

 Congo has said the first person died from the virus on April 24 in Bunia, and the body was repatriated to the Mongbwalu health zone, a mining area with a large population.

“That caused the Ebola outbreak to escalate,” said Kamba, the health minister.

When another person fell ill on 26 April, samples were sent to Congo's capital, Kinshasa, for testing, according to the Africa Centres for Disease Control. Bunia is more than 1,000 kilometres (620 miles) away in a country with some of the world's worst infrastructure.

Samples from Bunia were initially tested for the more common type of Ebola, Zaire, Congolese officials said. They came back negative, said Dr Richard Kitenge, the health ministry incident manager for Ebola, and local authorities assumed it was not the virus.

Only laboratories in Kinshasa and Goma, which are now controlled by the M23 rebel group, have the capacity to test for the Bundibugyo virus. It was not clear what measures the Rwanda-backed rebels were taking in the outbreak.

On 5 May, the WHO was alerted to about 50 deaths inMongbwalu, including four health workers. The first confirmation of Ebola came on 14 May.

“Our surveillance system didn't work,” said Jean-Jaques Muyembe, a virologist at the National Institute of Bio-Medical Research.

“The Bunia laboratory ... should have continued searching and sent the samples to the national laboratory. Something went wrong there. That's why we ended up in this catastrophic situation," he said, and asserted that members of parliament and senators were aware "there were deaths, and nothing was being said.”

This is a rare type of Ebola

 Ebola is highly contagious and can be contracted via bodily fluids such as vomit, blood or semen. The disease it causes is rare but severe and often fatal. During an outbreak over a decade ago that killed over 11,000, many were infected while washing bodies during community funerals.

“Ebola is very much a disease of compassion in that it impacts the people who are more likely to be taking care of sick folks,” said Dr Craig Spencer, an associate professor at the Brown University School of Public Health who survived Ebola more than a decade ago after contracting it in Guinea.

The US CDC says it causes fever, headache, muscle pain, weakness, diarrhoea, vomiting, stomach pain and unexplained bleeding or bruising. The severity of the symptoms and the rising caseload were fueling growing panic in Bunia neighbourhoods.

“I know the consequences of Ebola, I know what it's like,” said resident Noëla Lumo. She previously lived in Beni, a region hit by former outbreaks. When she heard about the latest one, she began making protective masks by hand.

The region already grapples with a humanitarian crisis

Eastern Congo has long grappled with a humanitarian crisis and the threat of armed groups that have killed dozens and displaced thousands in Ituri in the past year. Ituri already had over 273,000 displaced people out of a population of 1.9 million, according to the UN.

UN staff have been asked to work from home and avoid physical contact and crowded areas, said a Bunia-based UN official, who spoke on condition of anonymity because they were not authorised to speak publicly on the subject.

The most important challenge is breaking the virus transmission chain, Muyembe said.

“Of the 17 epidemics we have experienced in (Congo), 15 were brought under control simply by applying public health measures,” he said. “The disease is transmitted through contact with bodily fluids. If you avoid this contact, you break the chain of transmission, and the epidemic stops.”