As the World Health Organization warns about the Ebola outbreak in the Democratic Republic of the Congo, investigators still can’t identify how it started—an absence of answers that is reshaping how fast responders can contain cases and how fragile public trus
Ten days into the outbreak, the question still won’t go away: where did it begin?
In the summer of 1854, cholera killed 500 people in London’s Soho neighborhood in just 10 days. The city’s population had more than doubled to 2.3 million in the first half of the 1800s. and its sewage system couldn’t keep up. Streams of human waste flowed into the street and seeped into the water supply. yet they were considered unconnected to cholera. At the time, physicians blamed “bad air”—miasma.
John Snow, an English physician, argued the illness was waterborne. When he mapped cholera deaths in Soho, Snow found the victims relied on one specific water pump on Broad Street. He persuaded city officials to remove the pump’s handle, preventing others from using it. With the source eliminated, the outbreak—already past its peak—ended in days.
The logic Snow used is still at the center of modern epidemiology: when outbreaks spread, finding the source can prevent new cases. It also helps explain disease to a frightened public and guides the strategies health workers need for what comes next.
That’s why what’s happening now in the Democratic Republic of the Congo has become so difficult to manage—even as the world’s attention sharpens.
On May 17. the World Health Organization declared the Ebola outbreak in the DRC a public health emergency of international concern. the highest level of global health alert. As of June 2, it had killed 62 people and recorded 363 confirmed cases. The outbreak is the 17th Ebola outbreak in the DRC and one of the largest on record.
It has also crossed borders. By June 4, Uganda had 16 confirmed cases, one confirmed death, and one probable case and likely death.
The first confirmed case was a healthcare worker in Bunia, DRC, who died on April 24. Yet the outbreak may have been spreading undetected since as early as January. Investigators still haven’t identified patient zero—the index case—and still don’t know how this outbreak began.
Abdou Sebushishe. a doctor working with the International Medical Corps in Goma. DRC. said up to 20 percent of current patients are themselves healthcare workers. He estimated it may be more than six months before the outbreak could be controlled. given that the disease is outpacing the current response.
Part of the challenge is the virus itself. This outbreak is caused by the Bundibugyo strain of Ebola. which is relatively uncommon and has a genome about 30 percent different from the Ebola viruses that usually spark outbreaks. Testing for more common variants didn’t pick up the Bundibugyo virus right away.
Conflict in the DRC has compounded the problem, contributing to delays and making contact tracing difficult. Unlike some other Ebola strains, the Bundibugyo virus has no approved therapeutics or vaccines.
In past Ebola outbreaks, researchers sometimes managed to identify the index case. During the 2014–2016 West Africa Ebola epidemic—the largest and deadliest in history. with more than 15. 000 confirmed cases and 11. 000 deaths—investigators identified the first patient as a toddler in Guinea. The toddler died in December 2013 before the outbreak had been identified. Scientists have said it’s possible the child came into contact with an Ebola-infected fruit bat or its droppings while playing in a hollow tree. but they can’t say for sure.
Outbreak investigations can also inflame politics. Determining where and how infections begin can lead to international fingerpointing, similar to what characterized much of the Covid-19 pandemic. But the goal isn’t simply to assign blame. Knowing the origin of an outbreak helps responders halt transmission. communicate clearly with the public. and prevent—or at least prepare for—the next one.
Even in the United States, the work of identifying sources has had a tangible impact. New York City’s biggest and deadliest outbreak of Legionnaires’ disease began to be detected in the summer of 2015. but by then dozens had already been hospitalized. It was the second-largest Legionnaires’ disease outbreak in US history, infecting 138 people and killing 16.
Investigators began with contact tracing to find a shared exposure, but results didn’t point to any single common source. Cooling towers had been involved in previous Legionnaires’ outbreaks, but officials didn’t know how many cooling towers existed in the city or how well maintained they were.
They located and tested 55 cooling towers in the South Bronx, where cases were clustered. The source was identified as a single cooling tower atop the Opera House Hotel. The hotel disinfected the tower. and New York’s City Council passed new regulations requiring every building in the city with a cooling tower to register it with the health department. test it every 90 days. and remediate it if Legionella was found.
Within a year, the health department inspected almost 80 percent of the city’s towers. No large Legionnaires’ disease outbreaks emerged afterward—until inspections declined in 2025.
Jay Varma. a physician and epidemiologist who served as incident manager for the 2015 New York outbreak. wrote last year in Healthbeat: “Regulations do not enforce themselves.” He pointed to the Covid pandemic’s backlash against government authority and austerity budgets starving public health agencies. adding that “Infections may be inevitable. but outbreaks are a choice.”.
Haiti and Soho are far from Bunia and the Democratic Republic of the Congo. Still, the common thread is the same: tracing a source can change the odds of stopping an outbreak.
But when the source stays elusive—when the index case can’t be found, when the virus is harder to detect, when security prevents the close work of tracing—the health system is left trying to respond with gaps.
That problem isn’t limited to Ebola. Hantavirus and other emerging threats can take weeks to incubate, and delayed detection combined with human movement makes tracing the beginning more difficult.
In Ushuaia. Argentina—the southernmost city on the planet and the main gateway for cruise departures to Antarctica—a Dutch couple may have contracted the Andes virus. the only strain of hantavirus known to spread from person to person. before sparking an outbreak on the MV Hondius. The Argentinian government’s prevailing theory is that the couple got infected while birdwatching at a landfill in Ushuaia before the cruise. coming into contact with rodents that carry the Andes strain.
Omer Awan, a physician and public health expert, told me by email that the theory may not be plausible. He said the long-tailed pygmy rice rat responsible for spreading the Andes strain is usually found in northern Argentina or Chile. and that the birdwatching at the landfill occurred in the southern part of Argentina. He also said there have been no recorded cases of hantavirus in Tierra del Fuego province, where Ushuaia is located.
Awan added that understanding the origins of the outbreak would help guide interventions like rodent control and isolation protocols. and that it would help identify how the rare Andes strain of hantavirus is transmitted. He also said that identifying the source of the 2026 Ebola outbreak can influence response strategy and how public health officials monitor the virus.
There are reasons uncertainty can persist. Investigators still don’t know the original source of the first Ebola outbreak in 1976, which occurred in two simultaneous waves. Debates also continue over whether Covid-19 emerged naturally through zoonotic spillover—an animal-to-human jump—or if it escaped from a lab in an accident.
Even when events are understood to be natural in origin, political blame can shift. The text describes international efforts to shift “blame” from Argentina to neighboring Chile, with economic interests on the line.
Spillover events are becoming more likely as humans destroy ecosystems and infringe on animal habitats. Climate change is cited as worsening existing infectious disease risk. Neil Vora. executive director of Preventing Pandemics at the Source coalition. wrote in Time Magazine: “Because of our choices as a society. there’s a one-in-five chance that another pandemic will occur in the next decade that will kill at least 25 million people.”.
Determining outbreak sources has become even more politically perilous in the post-Covid era. The US and Argentina have pulled out of WHO. Global health funding cuts. including from the US and other countries. are described as weakening biosurveillance architecture and the ability to respond effectively to infectious disease threats.
Compared to Covid, the scale of the 2026 Bundibugyo and hantavirus outbreaks are small. Still, the inability to get answers quickly has real consequences.
The stakes stretch beyond outbreaks that are naturally occurring. Jaime Yassif. senior advisor for global biological policy and programs at the Nuclear Threat Initiative. told me that “artificial intelligence capabilities are advancing incredibly rapidly. ” and that could make it easier for novice actors to engineer pathogens already known. or for sophisticated actors to engineer novel pathogens more dangerous than those found in nature.
When an outbreak’s origin is uncertain—whether it’s natural. accidental. or deliberate—there may not be robust international mechanisms to investigate and arrive at conclusions quickly. The text describes a proposed Joint Assessment Mechanism to identify the source of outbreaks of uncertain origin. housed in the UN Secretary-General’s Mechanism for Investigation of Alleged Use of Chemical and Biological Weapons. to pull together components of the UN system and bridge security and public health.
Yassif said that project is currently on pause, adding that advocates couldn’t get the political will to move it forward despite support internationally.
If investigations can’t happen fast enough, public health officials face a harder job—stopping transmission, deciding what precautions to take, and maintaining international cooperation while suspicion grows.
That’s the tension embedded in this Ebola story: the outbreak is moving, but the first point on the map is still missing. And when you can’t find how it started, you can’t be sure you’re cutting off the right path.
Unless outbreaks can be traced—where and how they began—next time the consequences could be worse.
Ebola Democratic Republic of the Congo WHO public health emergency Bundibugyo strain contact tracing outbreak investigation John Snow epidemiology Legionnaires' disease Legionella New York City