Health officials in Democratic Republic of Congo (DRC) confirmed a fourth case of Ebola in Goma, a densely populated border city with Rwanda, on Thursday, identifying her as the wife of a gold miner who had traveled to an Ebola-infected area and returned with the virus.

The man was the second confirmed case of Ebola documented during the current outbreak in the city of Goma. The third is his one-year-old daughter.

Authorities are so far considering the three cases separate from the first identified Ebola victim in Goma, a pastor who died after traveling north to attend to an Ebola-stricken family and returned with the virus – meaning the current victims did not get the virus from the pastor and there are still no documented cases of anyone contracting Ebola in Goma outside of the current four.

The World Health Organization (WHO) declared the current outbreak a Public Health Emergency of International Concern in mid-July after authorities diagnosed the pastor. WHO Secretary-General Dr. Tedros Adhanom Ghebreyesus called the arrival of Ebola to Goma a “game-changer” that has alarmed the international humanitarian response community.

Despite Goma’s presence on the border with Rwanda – and a growing refugee crisis north in Ituri province, which borders Uganda – the WHO has energetically urged the countries involved not to shut down their borders. Rwanda appeared to temporarily shut its border down at Goma on Thursday but has since denied a permanent closure.

All cases of Ebola in the current outbreak have so far been documented in DR Congo except for three confirmed in Uganda, all three individuals who crossed the border to attend the funeral of an Ebola victim in DRC.

 The miner, who is believed to have contracted the virus in Ituri province, died on Wednesday, according to the Center for Infectious Disease Research and Policy (CIDRAP). Ituri borders the most affected area, North Kivu province, to its north. Goma lies on the southern limit of North Kivu province, near South Kivu.

CIDRAP notes that, despite concerns over a potential outbreak in Goma, “incidence rates haven’t changed since the WHO’s last weekly report. There were 79 new cases in the most recent week, along with 47 more deaths. The number of health workers infected in the outbreak has risen to 146.”

Authorities have quarantined 15 people in Goma, though they have identified 200 people who may have come into contact with the second Ebola victim in the city. Of those, 160 had reportedly received an Ebola vaccine. Despite Ebola’s arrival in Goma being recent, the local government began preparations to block the virus months ago in anticipation of such a development.

DRC marked the one-year anniversary of the current Ebola outbreak on Thursday.

Ebola responders working elsewhere in North Kivu came down to Goma on Thursday to begin expanding contract tracing measures, in which officials find all individuals who came into contact with confirmed Ebola patients and isolate them to stop the virus from spreading unchecked. The Congolese publication Actualité reported that a group of health workers are also active in Mungwalu, Ituri province, the area the miner visited before bringing the virus to Goma. Local officials say they have yet to diagnose a case of Ebola in Mungwalu.

The current Ebola outbreak is the second-worst on record after the 2014-2016 outbreak that swept Sierra Leone, Liberia, and Guinea, where it originated. The social and geographic context for the two outbreaks in completely different; in the 2014 outbreak, the virus was largely relegated to rural areas and, while attacks against Western aid workers occurred, the area was largely not a war zone. North Kivu and Ituri have been in a stage of guerrilla civil war for years as rival militias fight over control of the region’s natural resources. Butembo, Beni, and other affected cities are densely populated urban areas. Militia fighting is forcing families to flee across the regions Great Lakes into Uganda, where they face little customs processing, much less Ebola screening.

The militias have stopped fighting each other on occasion to burn down Ebola treatment centers and kill doctors, nurses, and other health professionals. Officials have documented as many as 200 attacks on health workers in Congo this year.

“This is the most difficult environment in which an Ebola response has ever been attempted,” Dr. David Gressly, the WHO’s Ebola Emergency Response Coordinator, told reporters on Thursday. “It’s a conflict zone and has been for the last 20-25 years, it’s an area of opposition politically that has felt marginalized with a high distrust of local authorities.”

Gressly blamed significant “interruptions” in public health measures for worsening the outbreak. “We need to stop the kinds of interruptions that have affected this response since the beginning: the attacks … but also other events, political demonstrations, strikes over non-payment of salaries [by health workers,” he noted. “The difficulty with an interruption, even for a day, is that it allows the virus to multiply … you often lose weeks over days of interruptions.”

Not all that is different, however, is worse. Health workers are now armed with an Ebola vaccine developed by the pharmaceutical company Merck that has been given to thousands of first responders, at highest risk for being exposed to the virus. The vaccine is 97 percent effective.

The vaccine has not entered Congo without controversy. Last week, former Congolese Health Minister Oly Ilunga resigned in part over pressure from the government to allow a second Ebola vaccine, manufactured by Johnson & Johnson, to be used in the field. Ilunga refused, noting that residents in affected areas were highly suspicious of Western medicine and doctors had struggled already to convince them to accept one vaccine. Introducing a second vaccine, one that requires two doses, would fuel conspiracy theories that humanitarian aid workers are deliberately poisoning Africans with Ebola as a form of population control. Ilunga’s resignation has opened the door for the second vaccine, which has not yet been tested in the field.

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