Angola is in the grip of the world's worst ever outbreak of Marburg virus.
According to the World Health Organization (WHO), as of 5 April, 156 of the 181 people reported infected have died.
The Ebola-like virus causes a fever that, in fatal cases, is usually accompanied by severe internal bleeding and shock.
There is no vaccine or medical treatment and up to 80 per cent of infected people die within three to seven days. Three-quarters of those affected are children under five.
Diagnosing an infection with the Marburg virus can be difficult as its initial symptoms are similar to those of malaria or tuberculosis. They include diarrhoea, stomach pains, nausea, vomiting and severe chest pains.
Moreover, before triggering any symptoms, the virus incubates for five to ten days.
The WHO believes the current outbreak began in October 2004 in Uige province.
Researchers in Uige and the Angolan capital Luanda are trying to develop faster methods of diagnosis so that infected people can be quarantined to stop the virus spreading.
A few research groups around the world are working on drugs and vaccines to fight the virus. One group in the United States showed last year that inactive virus particles injected into guinea pigs protected them from infection.
According to the WHO, close contact with the bodily fluids of infected people, for example in hospitals or at burials, has in the past increased the risk of infection.
In addition, patients often have respiratory problems and can spread the virus by coughing and sneezing. Health workers have been advised to wear a mask and gloves, but workers in Luanda say there is a shortage of equipment.
The virus was first identified in 1967 in laboratory workers in two German towns, Marburg and Frankfurt and in Belgrade, former Yugoslavia. The outbreak was linked to monkeys imported from Uganda.
The WHO and UNICEF (United Nations Children's Fund) are working with Angola's Ministry of Health to formulate a national plan of action to control the current outbreak.
The last outbreak, which killed 123 people, occurred in the Democratic Republic of Congo during 1998-2000.