At least 96 people have died in the past five months in Angola after an outbreak of a haemorrhagic fever in the north, caused by the Marburg virus.
The symptoms of Marburg disease are similar to Ebola
The World Health Organization says the disease, which has particularly affected children under five years old, is from the Ebola family.
The symptoms, similar to Ebola, include vomiting, bloody discharge and fever.
Correspondents say Angola's health infrastructure is in tatters after a 27-year civil war, which ended in 2002.
The nature of the outbreak was discovered after blood samples were sent to the US for analysis.
The Marburg disease, which was first recognised in 1967, affects humans and primates.
Vice Health Minister Jose Van Dunem said 101 cases of the illness had been reported in a hospital in the city of Uige.
Ninety-three people have died and two have left the hospital without being properly discharged, he told reporters.
"We are engaged in an effort with the community to find the two patients who fled the hospital and to detect new cases," he said.
He said he feared the Marburg epidemic could spread to other parts of the country, including the capital, Luanda.
WHO has suggested Angolan figures may include other deaths and said last week that at least 39 people have died.
WHO has had to cope with several outbreaks of Ebola in Africa since 2000.
The biggest was in Uganda four years ago, when hundreds died.
It passes quickly from person to person, through bodily fluids such as mucus, saliva and blood.