What is Marburg disease?
MARBURG virus disease is similar to Ebola and can spread fast from person to person.
It has a fatality rate of up to 88 per cent in patients who catch it, and has been found for the first time in West Africa.
Marburg is listed by the WHO as a top ten priority disease, meaning it poses "the greatest public health risk".
A patient was confirmed to be carrying to disease in West Africa for the first time after dying on August 2, in Guinea.
He was from the Gueckedou province near the borders of Sierra Leone and Liberia, with this case raising fears the virus could cross into those countries.
Dr Matshidiso Moeti, the WHO's regional director for Africa, said: “The potential for the Marburg virus to spread far and wide means we need to stop it in its tracks.
“We are working with the health authorities to implement a swift response that builds on Guinea’s past experience and expertise in managing Ebola, which is transmitted in a similar way."
Previous outbreaks and sporadic cases have been reported in South Africa, Angola, Kenya, Uganda, and the Democratic Republic of the Congo, but this is the first time the virus has been detected in West Africa.
What is Marburg virus disease?
The virus is from the same pathogen family as Ebola, but has no known treatments or vaccines.
Marburg virus was first identified in 1967 in both Marburg and Frankfurt in Germany, and in Belgrade, Serbia.
The outbreak was linked to labs using African green monkeys imported from Uganda.
It is transmitted to people via fruit bats and spreads between human through bodily fluids.
It has a two-21 day incubation period, according to the WHO.
What are the symptoms of the virus?
Illness caused by the virus usually begins quite quickly with severe symptoms such as high fever, headache and malaise.
Muscle aches and pains are also common, with abdominal pain, cramping, nausea and diarrhoea setting in on the third day.
Patients at this stage have often been described as "ghost-like", with extreme fatigue and drawn features.
A non-itchy rash has also been noted between two and seven days of the onset of symptoms.
Most patients then go onto develop haemorrhaging within a week, with fatal cases bleeding from multiple areas - such as the nose, gums and vagina.
If case persists for around 15 days, inflammation of the testicles has also been reported, along with high fever.
Death usually happens between eight and nine days after onset - largely due to severe blood loss and shock.
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There is as yet no proven treatment available for Marburg virus disease.
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However, a range of potential treatments including blood products, immune therapies and drug therapies are currently being evaluated.
Angola suffered the worst epidemic in 2005, when 90 per cent of the 252 people infected in the southern African country died.