Two outbreaks of the Marburg virus, a close cousin of Ebola which causes a severe and often fatal disease in humans, have been confirmed in Africa in recent months. It has sparked concern among health officials about the rare virus, which has no treatment or vaccine and a fatality rate of up to 88%, and its potential to spread.
The bat-borne virus started making headlines in February, when Equatorial Guinea confirmed its first-ever Marburg outbreak to the World Health Organization — since then, the country has reported 14 confirmed cases and 10 confirmed deaths.
The following month, Tanzania declared an outbreak of Marburg, which has caused eight confirmed cases and five deaths so far, according to the WHO.
On Thursday, April 6, the United States Centers for Disease Control and Prevention issued a health advisory to inform U.S. public health departments and clinicians about these outbreaks and increase awareness about the "potential for imported cases" — although no cases related to these outbreaks have been reported in the U.S. or any other countries outside Tanzania and Equatorial Guinea to date.
The CDC has also issued travel advisories for Tanzania and Equatorial Guinea, urging travelers to these countries to practice precautions, avoid contact with sick people and bats, and watch for symptoms for at least three weeks after leaving.
What exactly is Marburg, how does it spread, and what do people need to know about this outbreak?
What is the Marburg virus?
The Marburg virus was first identified in 1967 and has caused only a handful of outbreaks since, primarily in Africa, per the CDC.
"The Marburg virus is part of a family of viruses we call hemorrhagic fever viruses, and it's closely related to Ebola," Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells TODAY.com.
"The natural host or reservoir of the Marburg virus is fruit bats," Schaffner adds, but periodically the virus can leave the animal population, cross the species barrier and enter into the human population.
In humans, the Marburg virus causes Marburg virus disease (MVD), a severe and deadly hemorrhagic fever, a condition which can affect many organ systems and harm the cardiovascular system, according to the CDC.
The average fatality rate of Marburg is 50%, according to WHO, but the case fatality ratio of past outbreaks has ranged from 25% to about 90%, Amira Roess, Ph.D., professor of global health and epidemiology at George Mason University’s College of Public Health, tells TODAY.com.
According to the CDC health advisory, most experts agree that the outbreaks in Equatorial Guinea and Tanzania are two independent animal-to-human spillover events and there is no evidence to suggest these two outbreaks are related.
What are the symptoms of Marburg?
The initial symptoms of Marburg include a sudden fever, chills, headache and muscle aches, per the CDC. Within a few days, diarrhea, vomiting, nausea, sore throat and chest or abdominal pain may begin — some people experience a rash, Schaffner adds.
Severe symptoms typically begin five to seven days after onset, per WHO, and usually involve profuse bleeding (hemorrhaging) from multiple orifices, similar to Ebola, says Roess. The internal bleeding can cause bloody stool and vomit, the experts note, and a person may bleed from their nose, eyes or gums.
These symptoms can progress, and a person may experience rapid weight loss, liver failure, inflammation of the pancreas, delirium and multiorgan dysfunction, per the CDC. "It really involves the entire body," Schaffner notes. The blood loss and other symptoms can lead to death.
"There's this perception that people are always going to bleed out everywhere ... but that's not the case. ... Only when it's a very severe case do you have the hemorrhagic part of it," says Roess.
In the early stages or less severe cases, Marburg can look similar to typhoid or malaria, per WHO, making it difficult to diagnose. Marburg is diagnosed through laboratory testing, Roess adds.
How does the Marburg virus spread?
"It is transmitted when people come into close contact with infected bodily fluids, blood or contaminated surfaces, very similar to Ebola," says Roess. Marburg is not airborne, the experts note.
These bodily fluids include vomit, feces, urine, saliva, sweat, breast milk, amniotic fluid, semen and vaginal fluids, per the CDC, which can transmit Marburg virus to another person through broken skin or the mucous membranes in the mouth and nose, for example.
The virus often spreads in close environments or through families, says Schaffner. Transmission can occur when someone, whether a family member or health care provider, is caring for an infected person without proper infection control precautions, he adds.
The incubation period, or the time between exposure to an infection and symptom onset, is two to 21 days, per the CDC.
"In the early phases of the illness, the Marburg virus not very transmissible," says Dr. Peter Hotez, co-director of the Texas Children's Hospital center for vaccine development and neglected tropical disease expert, tells TODAY.com.
However, as MVD becomes severe or reaches the hemorrhaging stage, "you get huge numbers of virus particles in the body, even at death," says Hotez. People can also become infected while handling the body of someone who's recently died from Marburg, he adds.
How contagious is Marburg?
Compared to infections that spread through the respiratory route like COVID-19, Marburg spreads less easily since it requires direct contact with blood or bodily fluids, says Schaffner.
The "contagiousness" of a virus is described using something called a reproductive number or R0, which represents the average number of people one individual who gets the virus can infect, says Hotez.
Measles, which is at the very top of the scale, says Hotez, has a R0 between 12 and 18. "Ebola is closer to the bottom of the scale and Marburg presumably, as well. The R0 is more like one to two," Hotez explains.
Marburg can be controlled easily through proper isolation and case detection, says Hotez. It's also crucial that health facilities take strict infection control precautions and providers have adequate personal protective equipment (PPE) to prevent transmission, says Schaffner.
That said, Marburg outbreaks are very rare, and scientists are still trying to lean more about this mysterious virus. "One of the biggest problems is that we don’t know much about this virus because we don’t do a lot of research or surveillance," says Roess.
Marburg viral disease treatment and vaccine
There is no specific treatment for Marburg virus disease, says Roess. However, supportive care — such as rehydration with oral or IV fluids, oxygen or blood transfusions — can improve survival chances.
The mortality rate of Marburg can actually vary depending upon the resources available to provide supportive care, says Schaffner.
"There are no authorized or approved vaccines; however, there are some vaccine candidates that are in early phase 1 trials," says Roess.
WHO hopes to test one of these experimental Marburg vaccine candidates in Equatorial Guinea amid the current outbreak, NBC News previously reported. "The hope is that vaccines can be deployed as part of clinical trials in this situation they the way they were during the last Ebola outbreak," Roess adds.
One of the challenges ahead, says Schaffner, is determining whether vaccines that work in the laboratory also work in the field and can be deployed quickly enough during an outbreak.
How worried should people be about the outbreak?
"We should be worried for the people in Tanzania and Equatorial Guinea, but the threat to those of us at home (in the U.S.) is very, very low," says Schaffner. Those who are living or traveling to areas in close proximity to the outbreaks should take precautions and follow local public health instructions.
There have been a few incidences of someone acquiring a viral infection from an outbreak like the Marburg ones happening right now and then traveling back and becoming sick in the U.S. or Europe, says Schaffner, but this is very rare. "There is no immediate sense of concern," he adds.
"We are kind of distant observers of this and sending resources, both people from the CDC and physical resources, to Tanzania and Equatorial Guinea to help curtail these outbreaks," says Schaffner.
One question Hotez says he commonly gets is: Why are all these rare or novel diseases popping up right now? In recent years we've seen Marburg, COVID-19, mpox and more. Is it all a coincidence?
Hotez says no, and that it’s a combination of economic and social conditions and climate change “contributing to the big uptick in diseases transmitted from animals to humans.”
“It’s more than a coincidence,” he adds.