Rwanda is in the midst of its first outbreak of Marburg virus - an often fatal disease with symptoms similar to Ebola. So far, 46 cases have been recorded and 12 deaths. The source of the outbreak is still not known.
Seven hundred doses of an experimental vaccine against the virus have just been shipped from the US to Rwanda. The vaccine is currently being administered, largely to healthcare workers, who have made up the bulk of the victims so far.
The roll out is part of a clinical trial, so it will be a while before the vaccine's efficacy is known.
Marburg virus is named after the town in Germany where it first emerged. In 1967, there were simultaneous outbreaks at laboratories in Marburg and Belgrade in Serbia (then part of Yugoslavia). The outbreak was caused by African green monkeys imported from Uganda for use in experiments. Seven people died.
Since then, there have been several Marburg virus outbreaks in sub-Saharan Africa, including in countries bordering Rwanda.
Previous outbreaks have been reported in the Democratic Republic of Congo, Uganda and Tanzania. The most recent outbreaks were reported in Equatorial Guinea and Tanzania between February and June 2023, where nine cases were reported and six deaths.
Other countries that previously reported outbreaks include Angola, Ghana, Guinea, Kenya and South Africa. The outbreak in Angola in 2005 killed 300 people.
Outbreaks typically occur when people come in contact with infected green monkeys, pigs or Egyptian rousette bats (a type of Old World fruit bat) - a common carrier of the virus. These bats are often found in mines and caves. Once the disease jumps from an infected animal to a human - so-called zoonotic spillover - it can spread from person to person through bodily fluids or by contact with contaminated surfaces, such as bedding.
There are no antiviral drugs to treat patients. People infected with Marburg virus are kept hydrated and any blood loss is replaced through transfusion.
The incubation period, which is the time between the exposure to Marburg virus and the start of symptoms, is five to ten days. Symptoms of Marburg virus disease can appear suddenly and include fever, muscle pains, diarrhoea and vomiting.
The virus damages blood vessels and interferes with the ability of blood to clot, which can lead to uncontrolled bleeding from the nose, eyes, gums, rectum and, in women, the vagina. The disease has a very high "case fatality rate". Between 24 and 88% of people infected with Marburg virus die - usually through extreme blood loss and shock.
Marburg virus disease is not an airborne illness and is not thought to be contagious before symptoms appear. However, people can remain infectious for months after they have recovered, and pass the disease on through bodily fluids. Men are advised to wear a condom for a year after symptoms first appear.
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Looking for clues
The Rwandan authorities are working to identify the source of the outbreak, how far it has spread and when the first case occurred.
Although Marburg virus disease has been reported in seven of 30 districts in the east African nation, the readiness of unaffected districts is also being ensured to mitigate the spread and quickly identify any spillover.
The World Health Organization (WHO) is working with Rwanda's neighbouring countries, including the Democratic Republic of Congo, Burundi, Kenya, Tanzania and Uganda, to review their readiness to respond to the outbreak.
The WHO assesses the risk of the Marburg virus outbreak as "very high" at the national level and "high" at the regional level. However, at a global level, the risk remains low.
Manal Mohammed, Senior Lecturer, Medical Microbiology, University of Westminster
