The half dozen extra infections in recent days include some medical staff who were treating victims of the haemorrhagic fever which has swept the western Bundibugyo region since August.

"Four of our medical personnel, including a doctor and three nurses, have been isolated in Bundibugyo Hospital after catching the virus," said Dr. Sam Okware, head of Uganda's national hemorrhagic fever task force.

"We now have a team of experts on the ground to try and contain further spreading of the virus."

Genetic analysis of samples taken from some of the victims shows it is a previously unknown type of Ebola, making it the fifth strain, U.S. and Ugandan health officials say.

Ebola can cause internal and external bleeding.

Victims often die of shock, but symptoms can be vague, including fever, muscle pain and nausea. It is known to infect humans, chimpanzees and gorillas.

Uganda was last hit by an epidemic of Ebola in 2000, when 425 people caught it and just over half of them died, including a doctor treating victims.

An outbreak in neighbouring Congo this year infected up to 264 people, killing 187.