The rare Marburg virus has killed 174 people out of a total 200 cases, said Dr. Mike Ryan, director of alert and response operations for the World Health Organization.
"The situation right now in Angola is not under control yet," Ryan told reporters in Geneva. "This is still a crisis, and a health crisis on a national level."
A health official tells The New York Times that more than a dozen health care workers have been killed by the virus, including two doctors, and that many workers are quitting the town's hospital to protect their lives.
The disease first appeared in the northern province of Uige in October, and Ryan said officials had since seen some success against the virus there. Several deaths attributed to Marburg have been reported in four other provinces, but all the victims had been in Uige.
Two cases have been confirmed in Angola's capital, Luanda, but there has been no transmission of the virus there.
Like Ebola, Marburg is a hemorrhagic fever. It spreads through contact with bodily fluids and can kill rapidly. There is no vaccine.
To stop transmission, all possible Marburg contacts need to be followed up, and this is made more difficult by Angola's damaged infrastructure. Containing the virus requires "a profound commitment" from Angolan authorities and the international community, Ryan said.
WHO, the U.S. Centers for Disease Control and Prevention and Doctors Without Borders have deployed teams in Uige to combat the virus.
However, field workers have been attacked by townspeople accused of killing people who have been taken away sick and returned dead, the Times reports, forcing them to suspend their checks in two Uige neighborhoods.
The worst previously recorded outbreak of the virus killed 123 people in neighboring Congo between 1998 and 2000, the last known outbreak of Marburg.