What is Marburg virus, and how worrying is it?

Rwanda is battling its first-ever outbreak of the deadly Marburg virus, with 36 cases reported so far and 11 deaths.

The World Health Organization said this week the risk of the outbreak is very high in Rwanda, high across the African region, and low globally.

Marburg is a virus from the same family as Ebola. It causes a haemorrhagic fever and has an average fatality rate of 50%, according to the WHO, although rates have been as high as 88% in previous outbreaks. Early clinical care and rehydration can improve survival, the U.N. health agency says.

Symptoms typically include a sudden high fever and extreme headache, as well as vomiting and diarrhea, following by uncontrolled bleeding.

It was first identified in Marburg, Germany - hence the name - and Belgrade, Serbia in 1967, after laboratory work with African green monkeys from Uganda led to human infections. Since then, there have been outbreaks and sporadic cases in Angola, the Democratic Republic of the Congo, Kenya, South Africa and Uganda, the WHO says.

Marburg spreads to humans from prolonged exposure to mines or caves where Rousettus fruit bats live. It can also spread between humans, through direct contact with the bodily fluids of infected people, or with surfaces or materials contaminated with those fluids, such as blood.

There are no approved vaccines or treatments for Marburg, but there are a number of promising candidates that could begin trials soon, Rwanda's health minister has said. These include vaccine candidates developed by non-profit organizations including the Sabin Vaccine Institute, which has said it is working with Rwandan officials on the outbreak, as well as the International AIDS Vaccine Initiative (IAVI).

The team that developed the AstraZeneca COVID-19 vaccine at Oxford University began a trial of its Marburg candidate this summer in the UK, using similar technology.

Rwanda is also monitoring around 300 contacts of known cases. Around 70% of confirmed cases are healthcare workers from two health facilities in the capital, Kigali, although cases have been reported from seven of the country's 30 districts. As well as spreading in healthcare facilities, the disease can also spread at funerals for those killed by the disease, which involve close physical contact with the deceased in some cultures as they are prepared for burial, said Paul Hunter, a professor of medicine at the University of East Anglia.

Health authorities around the world are on the alert for any spread to neighbouring countries or beyond.

Yes - in 2021, Guinea reported West Africa's first ever case of Marburg. In 2022, Ghana declared its first ever outbreak, and Tanzania and Equatorial Guinea did the same in 2023. These generally small outbreaks were brought under control with public health measures. Scientists have said the increased frequency of the outbreaks seem to be linked to human encroachment on animal habitats.

The Rwanda outbreak is already one of the biggest ever.