As the Ebola outbreak spreads in the Democratic Republic of Congo, researchers are scrambling to learn more about the rare virus that has sickened hundreds of people. What they discover could prove crucial in helping turn the tide against a virus that, for now, is outpacing efforts to contain it.
The Bundibugyo virus is the cause of only two previous epidemics: one in Uganda which began in late 2007 and another in Congo in 2012.
The majority of Ebola outbreaks in Africa have been caused by the Ebola virus, one of the four Orthoebolavirus species that make people sick sporadically. The largest, from 2014 to 2016 in West Africa, which caused more than 28,600 cases and more than 11,000 deaths, fueled efforts to develop vaccines and treatments. As a result, countries including Congo have stockpiled vaccines and medicines in anticipation of future outbreaks.
But these efforts have been useless in the face of the Bundibugyo virus.
The viruses that cause Ebola are “similar, but they are different,” says Thomas Geisbert, a virologist at the University of Texas Medical Branch at Galveston. Each is genetically distinct so that vaccines or treatments designed for one virus may be largely ineffective against another.
But viruses share a dark history: of the four Orthoebolavirus Of the species that infect humans, three cause the same serious illness, including fever, vomiting, bleeding and, sometimes, death. (The fourth only infected one person.) “The course of the disease may be different and the mortality rates may be different,” Geisbert says. “But in fatal cases, the outcome, the illness towards the end, is about the same.”
The race is on to find answers that could help combat this epidemic and prevent future outbreaks. Here are three big questions about the Bundibugyo virus.
How will the characteristics of Bundibugyo affect the trajectory of this epidemic?
Knowing this could help public health officials and health care workers prepare and determine the best ways to allocate resources.
The Ebola virus is the deadliest Orthoebolaviruswith mortality rates of up to 90 percent without treatment. It is also known as Zaire, the name of Congo when the virus was first isolated there in 1976. In comparison, about 30 to 50 percent of patients died in Bundibugyo’s two outbreaks, although it is unclear why the virus appears to be less deadly.
In the current outbreak, there have been 330 confirmed cases as of May 31, including 49 deaths. Another 116 suspected cases are under investigation. Most are in Congo, but a few are in neighboring Uganda.
Studies in nonhuman primates — the closest animal model that mimics what happens in infected people — show that at a high dose, “in the worst case,” Ebola is “uniformly deadly” without treatment, Geisbert says. All infected macaques die approximately five to nine days after exposure.
Bundibugyo virus infection, while still serious, is not as deadly. About a quarter of animals infected with Bundibugyo usually survive. But animals tend to stay sick longer. Those who die succumb approximately 14 to 15 days after infection.
It’s unclear what this means for the ongoing outbreak in Congo. “We can’t predict that; it’s way too early,” Geisbert says. Although a relatively low case fatality rate would be good news, a longer infectious period is “not a good thing” because it could prolong the epidemic. Ebola infections are contagious not only when patients have symptoms, but also after they die.
Krutika Kuppalli notes that “mortality rates are influenced by many factors beyond the virus itself.” The infectious disease doctor at UT Southwestern Medical Center in Dallas led an Ebola treatment unit in Sierra Leone during the 2014 outbreak in West Africa. How quickly cases are detected and the strength of and access to health care resources may factor into survival rates.
This Bundibugyo outbreak caught officials off guard in part because cuts in international aid in the region has slowed disease surveillance and response. Additionally, because vaccines and treatments were designed for Zaire Ebola, there are no vaccines or treatments available to protect people against Bundibugyo.
For now, managing an outbreak that has spread widely due to late detection is the immediate concern. It’s important to ensure people get the care they need — including fluid management to help with blood loss — in a region experiencing ongoing conflict, Kuppalli says. “High-quality supportive care saves lives. »
Which animal harbors the Bundibugyo virus?
Know where the Bundibugyo virus is located hides between epidemics could help experts build guardrails around potential sources of infection. But for now, it remains a mystery.
While the first known cases of Ebola disease were documented in 1976, it was not until 2007 that the first outbreak linked to the Bundibugyo virus was detected. The reason Bundibugyo rarely causes outbreaks could be because the virus is rare in nature, Kuppalli says. It could also be that authorities misclassified past outbreaks or missed them due to limited surveillance. Or, people do not often encounter animals carrying the Bundibugyo virus.
“One of the problems with Ebola is that we’re still trying to figure out what the reservoirs are,” says Kartik Chandran, a virologist at the Albert Einstein College of Medicine in New York. Previous studies largely pointed to fruit bats as the source, although insectivorous bats can also be involved in the spread of viruses to humans. Preliminary genetic analyzes suggest that the current outbreak is the result of a new unique overflow from an unknown reservoir to humans.
Orthoebolavirus including Bundibugyo maybe able to slip inside cells of a variety of African bats, Chandran and colleagues reported in 2025 in Cellular host and microbe. Species including the hammerhead bat (Monstrous Hypsignathus) and the hairy split-faced bat (Cold night) have emerged as possible reservoirs that harbor the viruses without getting sick themselves. Another global study published May 19 on bioRxiv.org suggests that the Angolan free-tailed bat (Condylure mop) is worth keeping an eye on.
Researchers are getting closer, Chandran says. But “there is still a lot of mud on the ground”.
Could the vaccine and treatments developed to fight the Zaire Ebola virus work against Bundibugyo?
Knowing which treatments might be effective could give public health workers some additional tools to try to contain this outbreak. It could also buy some time to see if Bundibugyo-specific vaccines and treatments that have been tested on animals will work in humans.
But that’s not likely. The Bundibugyo virus is different enough from the Zaire Ebola virus that experts doubt whether the tools will be effective in curbing the epidemic.
Lab-made antibody treatments target a wine glass-shaped protein called a glycoprotein. Glycoproteins cover the surface of the virus, but those found on various Orthoebolavirus are constructed with different protein building blocks.
Antibody treatments approved and effective against the Zaire virus “are going to be DOA right off the bat” during the Bundibugyo outbreak, Chandran says. These antibodies cannot attach to parts of the glycoprotein that differ between the two viruses. Zaire virus treatments are essentially blind to Bundibugyo virus replication in the body.
But in 2017, Chandran and his colleagues discovered antibodies from a survivor of the Ebola outbreak in West Africa. capable of attacking not only the Zaire virus but also its close cousins. Two of these antibodies were eventually developed into a cocktail called MBP134 which was found to effective in protecting ferrets and macaques from Zaire and Bundibugyo, as well as the virus from Sudan, the third Orthoebolavirus it’s deadly for people.
“It’s real therapy,” says Chandran. “It’s not just a prophylactic. You can give it after the animal is already sick and it reverses the disease and almost completely cures the animals.”
The treatment worked on animals with advanced disease, says Geisbert, who also participated in the testing. This would be useful in the event of an epidemic. But the drug is administered intravenously, which can be difficult in resource-limited areas like Congo. “An oral antiviral would be fantastic in this situation,” he says.
Congolese public authorities plan to test MBP134 in clinical trials during the ongoing outbreak, along with an antibody treatment from drug developer Regeneron. (Regeneron is a major funder of the Society for Science, which publishes Scientific news.) The antibody treatment – a cocktail of three antibodies, one of which could work against Bundibugyo – is approved by the US Food and Drug Administration for use against the Zaire virus.
There is also an oral medication on the table. The antiviral, called obeldesivir, may protect macaques against develop illness after exposure ion to the Zaire virus, but has not yet been tested in humans.
There are also several vaccine candidates attacking the Bundibugyo glycoprotein, but none are ready for deployment, Geisbert says. One candidate is based on Ervebo, a vaccine approved for Zaire epidemics. Macaque studies show that the Bundibugyo version of the vaccine protects macaques from disease not only before exposure, but also after.
“It’s really encouraging,” says Geisbert. But it’s difficult to draw definitive conclusions because the study only looked at a handful of animals, he adds. Additionally, manufacturing a vaccine that could be used in human clinical trials could take months. The World Health Organization estimates that modified Ervebo shot could be available in seven to nine months. The Coalition for Epidemic Preparedness Innovations, an organization that funds vaccine development, is accelerate the development of this vaccine and two others in the hope of starting clinical trials as quickly as possible.
However, waiting several months is not fast enough to reverse the trend of this epidemic in the near future. “The hope,” says Chandran, “is that we come out of this with some sort of weaponry for next time.”