All your questions about Marburg virus answered

Rwanda is facing its first ever Marburg virus outbreak. Beginning in late September, 62 cases and 15 deaths had been reported by 17 October, mostly among healthcare workers in Kigali, the capital city.

More than 800 contacts of infected people have been followed up in an effort to catch infections early and prevent further transmission, two of whom travelled to Belgium and Germany but were given the all-clear. As of October 21, no new cases or deaths had been reported in six days, but the threat of the outbreak hasn’t gone away.

What is Marburg virus and what are its symptoms?

Marburg virus is from the same family of viruses as those that cause Ebola, which are “among the most lethal pathogens known to infect humans”, according to a perspective article in The New England Journal of Medicine.

They can cause similar symptoms, such as fever, chills and headache, as well as muscle aches and pains. Within a few days, people may develop a rash on their chest, back and abdomen. They may also experience nausea, vomiting and diarrhoea.

Marburg virus damages blood vessels and disrupts clotting, which can lead to blood in vomit and faeces, as well as bleeding from the nose and gums. In extreme cases, the infection causes internal bleeding and sepsis, which can lead to organ failure and death.

Where do outbreaks usually occur?

The virus was first identified in 1967, after one-off outbreaks in the German cities of Marburg and Frankfurt, and in Serbia’s capital, Belgrade. These cases were linked to lab experiments to improve polio vaccines that involved African green monkeys (Chlorocebus aethiops) from Uganda.

Since then, the virus has typically caused a few outbreaks per decade, often in East African countries such as Uganda, as well as its neighbour the Democratic Republic of the Congo (DRC), which is in Central Africa.

The virus was identified in Guinea, in West Africa, in 2021. Outbreaks have since occurred annually in different parts of the continent. For example, Ghana had its first outbreak in 2022 and Equatorial Guinea had its first cases last year. The Egyptian fruit bat (Rousettus aegyptiacus) lives in different parts of Africa and can carry Marburg virus, says Emma Thomson at the University of Glasgow, UK.

Exactly why outbreaks seem to be occurring more frequently is unclear. It could be down to improved case surveillance and people coming into contact more regularly with Egyptian fruit bats, says Thomson. Miles Carroll at the University of Oxford thinks the same.

People can catch Marburg virus if they visit caves or work in mines where the bats live. This may be happening more, but increased deforestation is also bringing people closer to these animals, says Carroll.

How deadly is it?

Marburg virus’ fatality rate has varied hugely from 24 per cent to 88 per cent in past outbreaks, similar to the 25 per cent to 90 per cent fatality rate seen with Ebola.

The range in mortality rates is probably due to differences in the capacity of countries to detect cases and the resources of their hospitals, say Thomson.

On 20 October, the World Health Organization’s director-general Tedros Adhanom Ghebreyesus released a statement saying that the agency is impressed with the level of critical care people have been receiving in Rwanda. He referred to two people with multiple organ failure who were on life support and had received mechanical ventilation. “We believe this is the first time patients with Marburg virus have been extubated in Africa,” he said. “These patients would have died in previous outbreaks.”

Rwanda’s ongoing outbreak is the third largest so far, for both cases and deaths. It comes behind the DRC’s outbreak in 1998 to 2000, when 154 cases were recorded and 128 people died, and Angola’s outbreak from 2004 to 2005, when 252 people were infected and 227 died.

Who is most at risk?

There have been relatively few known cases since Marburg virus was identified, which makes it difficult to know who is most at risk of severe infection, says Thomson. But those with suppressed immune systems, such as people who are older or pregnant, are probably more vulnerable, she says.

Few cases have ever been reported during pregnancy, but the European Centre for Disease Prevention and Control says the infection is generally more severe during pregnancy, when immune function is altered anyway.

Ebola is also more severe among older people, so the same is probably true for Marburg virus, says Thomson.

How do you catch it?

Genetic sequencing of cases in Rwanda has revealed that the virus jumped from an animal, like an Egyptian fruit bat or an African green monkey, to a person just once in the ongoing outbreak, the country’s health minister tweeted on 20 October.

The remaining transmission therefore happened between people. This can occur if viral particles in someone’s blood or other bodily fluid enters another person’s body through broken skin or via their eyes, nose or mouth. Burial ceremonies where people touch the deceased body of an infected person also raise the risk of transmission.

There is no evidence that Marburg virus spreads through droplets that are expelled when an infected person breathes, talks, coughs or sneezes, says Carroll.

How is it treated?

No drugs have been approved to specifically treat Marburg virus. People who require hospital care are usually given intravenous fluids to replace the water they lost through vomiting and diarrhoea. Painkillers can also help ease discomfort.

In 2021, researchers found that combining the antiviral drug remdesivir with antibodies against the virus protected four out of five rhesus monkeys from lethal doses of the infection. On 15 October, Rwanda started trialling the approach in people.

Is there a vaccine?

There is no approved vaccine against Marburg virus, but researchers are trialling an experimental one in Rwanda, where 1700 doses had been delivered and 669 doses administered as of 14 October.

This vaccine’s regimen consists of a single shot that contains the engineered genetic sequence of an adenovirus, which cause cold-like symptoms. Researchers have tweaked the adenovirus to contain a protein that Marburg virus uses to infect cells. Once injected, the adenovirus enters cells and produces copies of the virus protein, so the immune system can learn to recognise it.

Vaccinating the contacts of infected people would probably be the most efficient use of vaccine doses to slow the virus’s spread, says Thomson.

What is the risk this outbreak will leave Rwanda?

Rwanda has ramped up testing among the contacts of infected people, who are being quarantined, but there is still always the potential for the virus to spread, says Carroll.

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“The possibility of local spread within the region to neighbouring countries is currently very concerning,” says Thomson. Rwanda shares borders with Uganda, Tanzania, Burundi and the DRC. The virus could also spread further afield in Africa or even cause occasional cases elsewhere in the world if people travel to these areas, she says.

In early October, a platform of Hamburg train station was cordoned off after two passengers with suspected Marburg symptoms who had recently visited Rwanda were onboard a train from Frankfurt. They were later confirmed not to have the virus.

Countries need to warn people travelling from Rwanda about the risks and signs of a Marburg infection, says Carroll. If someone then develops symptoms, they can get screened and quarantined rapidly before an outbreak starts elsewhere, he says.