Here's what's happening with the Marburg virus outbreak in Rwanda

A deadly, Ebola-like virus called Marburg is currently causing an outbreak in Rwanda. The country declared an outbreak of Marburg virus disease on Sept. 27 and has reported 58 confirmed cases and 13 deaths as of Oct. 8. Many of those who have been infected are health-care workers.

While nearly all previous outbreaks have occurred in other sub-Saharan African countries—including Uganda, the Democratic Republic of the Congo, and Angola—this is Rwanda’s first. The government is responding by ramping up contact tracing, expanding testing, and deploying experimental vaccines and therapeutics in a clinical trial setting. Meanwhile, Sabin Nsanzimana, Rwanda’s health minister, has urged people in the country not to panic but to keep a close eye on symptoms and quickly seek medical help.

What is Marburg virus?

Like Ebola, Marburg is an RNA virus belonging to the family of filoviruses. Egyptian fruit bats are the primary reservoirs of Marburg virus. “It is always possible there may [also] be other animal hosts,” says Tracey Goldstein, director of Colorado State University’s One Health Institute, “but to date none have been found.”

Humans can get infected when they enter caves or mines where these fruit bats roost and come in contact with the animals’ infected saliva, urine, and feces. During the 1998–2000 Marburg virus outbreak in Congo that recorded 154 cases and 128 deaths, for example, most infections occurred among gold miners and their families. But the virus was first detected in 1967 when hemorrhagic fever ensued among laboratory staff in Marburg and Frankfurt in Germany and Serbia’s capital city of Belgrade. Scientists traced the outbreak to African green monkeys these laboratories had imported from Uganda.

What are the symptoms of Marburg virus disease?

The disease, formerly known as Marburg hemorrhagic fever, begins with flu-like symptoms, including fever, headache, fatigue, and muscle pain. On day 3 or 4, individuals experience nausea, vomiting, diarrhea, and belly pain. “A minority of people don’t get too sick, and then they get better,” says Armand Sprecher, an emergency physician and epidemiologist for Doctors Without Borders. He has been involved in on-ground filovirus outbreak responses, including the 2004–2005 Marburg virus disease outbreak in Angola—the largest ever recorded—that killed 227 of the 252 people who were infected. But “a larger number of people tend to get sicker and sicker,” he adds.

A small portion of individuals also experience bleeding around the gums, under their skin, in their stool or vomit, or from small punctures made by injection needles. “The name hemorrhagic fever is a little misleading because it sort of implies that [bleeding] is going to be a common feature of the severe form of this illness,” Sprecher says. “It’s really not all that common.”

Within 2 weeks, the virus can spread throughout the body and cause multiorgan failure. The virus infects immune cells and uses them to reach different parts of the body, says Elke Mühlberger, an immunologist and virologist at Boston University with expertise in highly pathogenic filoviruses. “What we still don’t know is what makes these viruses [such as Marburg] so pathogenic.” On average, around 50% of the infected people die.

How does the disease spread?

Marburg virus spreads when humans come in direct contact with body fluids such as blood, urine, saliva, feces, or semen of infected individuals. “So, people who are changing the bedding, doing the laundry, caring for people who are too weak and bedbound are at high risk,” Sprecher says. These individuals often tend to be health-care workers and family members.

Are there any vaccines or therapeutics for Marburg virus?

Currently, there are no licensed vaccines or therapeutics for Marburg virus disease, and care is typically supportive. Care includes hydration, managing oxygen levels and blood pressure, and treating secondary infections.

But, on Oct. 6, the Rwandan government announced that it will be deploying 700 doses of an experimental vaccine that it received from the nonprofit Sabin Vaccine Institute. The Washington, DC–based nonprofit says it’s partnering with Rwandan officials to vaccinate health-care providers and other adults at high risk—including close contacts of confirmed cases—as part of a Phase 2 clinical trial.

Sabin’s single-dose vaccine uses a chimpanzee adenovirus vector that expresses the Marburg virus glycoprotein to elicit protective antibodies. The vaccine was effective in protecting monkeys against the virus, and a Phase 1 clinical trial found that the vaccine was safe and induced an immune response when given to 40 healthy adults in the US. An ongoing Phase 2 trial to test the vaccine’s safety and immunogenicity is also underway in Uganda and Kenya.

Meanwhile, in Rwanda, in a clinical trial setting, government agencies are also rolling out an experimental monoclonal antibody called MBP091, which was developed and is being tested by Mapp Biopharmaceutical. The antibody was protective against Marburg in monkeys and was shown to be safe in humans in a Phase 1 clinical trial.

Additionally, Gilead, the company that produces the antiviral remdesivir, said last week that it would donate around 5,000 vials of the drug for emergency use to respond to the outbreak in Rwanda. Scientists reported in a 2021 study that when monkeys were infected with Marburg virus and treated 5 days later with either remdesivir or a monoclonal antibody, most of the animals survived. When researchers combined the treatments, most of the monkeys survived even when treated 6 days after infection.

An advantage to using remdesivir is that its safety in humans has already been assessed in clinical trials for COVID-19 and Ebola, according to Thomas Geisbert, a virologist at the University of Texas Medical Branch who led the 2021 study.

Scientists are continuing to develop additional vaccine candidates against Marburg, including one being advanced by researchers at the University of Oxford that also uses a chimpanzee adenovirus vector. Two additional candidates that have been tested in monkeys employ a recombinant vesicular stomatitis virus vector that has been altered to express the Marburg glycoprotein.

Sprecher says that outbreak periods are when Marburg vaccine developers can gather data on the efficacy of their products in humans, which could make obtaining licensure from regulatory agencies challenging. While it’s fortunate that outbreaks of the disease don’t infect thousands of people like some of the worst Ebola outbreaks have, that factor may also make testing new products for Marburg challenging, says Sprecher.