The Marburg virus has killed more than 140 people in a major outbreak in Angola.

Q: What is the Marburg virus?
It is a severe and highly contagious form of haemorrhagic fever caused by a virus from the same family - the filoviruses - as Ebola, although it is not as deadly as its cousin.

The virus was first discovered in 1967, during simultaneous outbreaks at laboratories in the former Yugoslavia and Frankfurt and Marburg, Germany.

Health officials linked the infections to contact with green monkeys imported from Uganda for research on a polio vaccine.

Q: What are the symptoms?
During the incubation period, which lasts between five and 10 days, no symptoms are apparent.

After that patients develop a flu-like illness with fever, chills, headache and aching muscles. Nausea and vomiting are also common.

The disease can then become increasingly damaging, causing jaundice, delirium, liver failure, and extensive haemorrhage, which can give rise to bloody diarrhoea and vomiting of blood (heamatemesis).

About one in four people infected with the virus die, usually from shock or liver failure. However, in areas where medical support is poor, the death rate can be much higher.

The infection can be difficult to diagnose, because many of the initial signs are similar to those of other infectious diseases, such as malaria or typhoid fever.

Q: Can patients make a full recovery?
Yes. But this can take a long time, and some suffer from related conditions such as hepatitis, inflammation of the spinal cord and eye problems.

Q: How is it spread?
How the virus jumps from animals to humans is not known.

Once a human is infected they can pass the virus on to others through their body fluids, most commonly blood.

Experts say it is possible that patients spread the virus by producing an aerosol of tiny infected droplets when they cough and splutter.

However, sick humans apparently do not usually generate sufficient amounts of infectious aerosols to pose a significant hazard to those around them.

Q: How is it treated?
There is no cure. However, death rates can be kept down by providing patients with medical support.

The key is to try to prevent patients from becoming dehydrated.

Q: Should health workers take precautions?
Yes. If possible they should wear gloves and masks.

Q: How common is it?
Experts believe the virus is rare and only found in Africa.

Cases have occurred in Uganda, Kenya, Zimbabwe and Angola.