What do we know about the Bundibugyo strain of the Ebola virus?

A rare strain of Ebola has prompted the World Health Organization to declare a public health emergency of international concern. Most reported cases have been recorded in the Democratic Republic of the Congo, with more than 100 suspected deaths and nearly 400 suspected infections as of Monday.

Health authorities are monitoring an outbreak caused by a little-known variant of the Ebola virus known as Bundibugyo Ebola. Here is what is currently understood about the strain, its risks, and ongoing response efforts.

WHAT IS BUNDIBUGYO EBOLA?

The ongoing outbreak—so far reported in the Democratic Republic of the Congo and Uganda—has been linked to the Bundibugyo strain of the Ebola virus. The strain was first identified during an outbreak in 2007–2008 in Uganda’s Bundibugyo Province. A second outbreak was later recorded in 2012 in the Democratic Republic of the Congo.

Bundibugyo Ebola is considered less deadly than the more widely known Zaire strain. Studies estimate that it causes death in approximately 30% to 40% of infected individuals, compared with fatality rates of up to 90% for the Zaire variant.

The virus is one of four species within the Ebolavirus genus that can cause severe and often fatal illness in humans. Transmission occurs through direct contact with infected bodily fluids from humans or animals, or with surfaces and objects contaminated by these fluids.

Healthcare workers are especially at risk due to exposure to infected patients. In the current outbreak, a U.S. physician working in the Democratic Republic of the Congo has also been reported infected.

SYMPTOMS AND DISEASE PROGRESSION

According to the World Health Organization, Ebola infections typically begin with sudden flu-like symptoms, including fever, fatigue, weakness, muscle pain, headache, and sore throat.

As the disease progresses, patients may experience vomiting, diarrhea, and in severe cases, internal and external bleeding. Advanced infection can lead to organ failure and death.

ARE THERE TREATMENTS OR VACCINES?

At present, there are no approved vaccines or specific antiviral treatments for the Bundibugyo strain. Any use of experimental therapies would require emergency authorization from health regulators.

Several investigational approaches have shown potential in laboratory or animal studies, including vaccine candidates and antiviral treatments previously tested against other Ebola strains. These include experimental vaccines and antibody-based therapies developed by multiple pharmaceutical groups.

Researchers are also evaluating newer antiviral drugs and early-stage vaccine platforms, including mRNA-based candidates that have shown preliminary success in animal studies. However, most have not yet progressed to human trials for this specific strain.

In the absence of approved medical treatments, outbreak control relies heavily on public health measures. These include rapid case detection, isolation of infected individuals, contact tracing, infection prevention protocols in health facilities, safe burial practices, and strong community engagement.

Experts note that these interventions were critical in controlling past Ebola outbreaks, including the 2014–2016 West Africa epidemic, the largest recorded Ebola outbreak in history.

IS THERE A TEST FOR BUNDIBUGYO?

Diagnostic tests for Bundibugyo Ebola do exist, but they are not widely available in all regions. Early in the current outbreak, standard testing methods failed to detect the strain because they were not designed to identify this specific variant.

As a result, initial cases produced false-negative results, delaying the public health response.

Health experts warn that such diagnostic gaps can allow the virus to spread undetected across regions before containment measures are fully activated.

HOW BUNDIBUGYO DIFFERS FROM OTHER EBOLA STRAINS

Genetic differences between Bundibugyo and other Ebola viruses affect how the disease behaves, how it is diagnosed, and how it responds to potential treatments.

Compared with the Zaire strain, Bundibugyo tends to replicate more slowly in the body. It also appears to take longer to overwhelm immune cells, which may influence disease severity and progression.

The incubation period is similar across both strains, typically ranging from 8 to 10 days, though it can extend up to three weeks in some cases.

Some research on survivors of previous Bundibugyo outbreaks suggests that long-term effects on organs such as the liver and kidneys may be less severe than those associated with the Zaire strain. However, survivors can still experience lasting health complications.

OUTLOOK

Health authorities continue to focus on containment efforts aimed at limiting further spread of the virus. Rapid detection, strengthened surveillance systems, and coordinated international support remain key priorities.

Officials emphasize that while Bundibugyo Ebola is less lethal than some other strains, it still poses a serious public health threat due to its ability to spread quickly in communities with limited healthcare infrastructure. -Reporting by Nancy Lapid; Editing by Caroline Humer and Bill Berkrot/Reuters