Scientists and health officials are racing to understand a rapidly expanding outbreak of the rare Ebola Bundibugyo strain in the Democratic Republic of Congo, warning that critical knowledge gaps are complicating efforts to identify infections, treat patients and slow transmission.
Since Congolese authorities declared the outbreak in mid-May, more than 1,100 cases and nearly 300 deaths have been reported, making it the largest known outbreak of the Bundibugyo strain since the virus was first identified. Neighboring Uganda has also confirmed 20 cases and two deaths linked to the outbreak, raising concerns about cross-border transmission.
Health experts say the scale and speed of the outbreak have exposed how little is known about Bundibugyo Ebola compared with the more familiar Ebola Zaire strain, which caused the devastating West African epidemic between 2014 and 2016.
“We’re facing an outbreak that we’re just, to be honest, beginning to understand,” World Health Organization emergencies director Chikwe Ihekweazu told reporters on Wednesday. Previous Bundibugyo outbreaks were far smaller, causing roughly 200 cases combined during outbreaks in Uganda in 2007 and Congo in 2012.
Although Bundibugyo belongs to the same filovirus family as Ebola Zaire and causes many of the same symptoms, including fever, vomiting and diarrhea, researchers say important differences are emerging that may be affecting both diagnosis and patient behavior.
One of the biggest challenges is detection. The outbreak initially spread undetected because commonly used Ebola tests are designed primarily to identify the Zaire strain. By the time health authorities confirmed Bundibugyo Ebola as the cause, transmission had already become widespread in parts of eastern Congo.
Compounding the problem is the absence of approved vaccines or treatments specifically targeting the Bundibugyo strain. While experimental treatment trials are expected to begin next week, doctors currently rely largely on supportive care to improve survival chances.
Medical workers on the front lines say limited knowledge of how the disease progresses is also affecting community response. Early symptoms often resemble common illnesses such as malaria, making it difficult for patients and healthcare workers to distinguish Ebola infections during the initial stages.
“For those at the early stage of the disease, it looks milder than Zaire, and I believe that is one of the reasons we are seeing more than 50% of patients at an advanced stage,” said Abdou Sebushishe, a senior adviser with the International Medical Corps, which operates several Ebola treatment centers in eastern Congo.
The perception that the illness appears less severe at first may be causing some patients to delay seeking medical care, allowing transmission chains to continue undetected.
Another key difference appears to involve bleeding, one of the most recognizable symptoms associated with Ebola outbreaks. In communities affected by previous Ebola epidemics, many residents still associate the disease with visible hemorrhaging.
However, early evidence suggests bleeding is significantly less common in the current Bundibugyo outbreak.
Research released Wednesday by scientists at Congo’s National Institute for Biomedical Research found that only about 10% of 505 confirmed patients studied experienced bleeding symptoms. That figure is substantially lower than historical estimates suggesting roughly 40% of Ebola patients experience some form of hemorrhaging.
According to Dr. Emmanuel Musingusi Bulemu, a Congolese health official investigating cases in Ituri Province, the absence of visible bleeding has fueled skepticism among local residents who lived through previous Ebola outbreaks dominated by the Zaire strain.
“As a result, people in the community say, ‘Before, it was bleeding. We haven’t seen any bleeding in our sick relative, so you’re lying to us,’” Musingusi said. “That perception strengthens resistance to the response efforts.”
Such resistance has emerged as a major obstacle for health authorities. Aid organizations report that mistrust, misinformation and occasional violence directed at healthcare workers have hampered surveillance activities and delayed treatment efforts in some communities.
The outbreak is unfolding in eastern Congo, a region that has long struggled with insecurity, armed conflict and weak healthcare infrastructure. Those conditions have complicated efforts to trace contacts, isolate patients and establish treatment centers.
Scientists say that despite the unique characteristics of the Bundibugyo strain, the fundamental public health response remains similar to previous Ebola outbreaks. Rapid testing, isolation of infected individuals, contact tracing and supportive medical care remain the most effective tools available.
“It’s the same things,” said Peter Piot, a professor at the London School of Hygiene and Tropical Medicine and one of the scientists involved in the original discovery of Ebola. “But I have never seen this many cases this quickly.”
Piot warned that the outbreak’s location presents additional challenges that could prolong transmission and increase the eventual toll.
“Without peace, I fear we will not stop this outbreak,” he said.
The growing crisis has heightened concern among international health agencies that the outbreak could continue expanding if containment measures fail to keep pace with transmission. Officials are particularly worried about the possibility of wider regional spread given confirmed cases already detected in Uganda.
As treatment trials prepare to begin and researchers gather more data on how Bundibugyo Ebola behaves, health authorities hope new findings will improve diagnosis and patient care. For now, however, scientists acknowledge that they are confronting one of the least understood forms of Ebola while responding to its largest outbreak on record.
With cases continuing to rise and healthcare workers struggling against logistical, medical and security challenges, the outbreak has become a test of whether existing Ebola response systems can adapt quickly enough to a virus variant that remains, in many ways, poorly understood.
