KAMPALA A new strain of the deadly Ebola virus has infected 51 people and killed 16 in an area of Uganda near the border with Democratic Republic of Congo, U.S. and Ugandan health officials said on Thursday.
"The mysterious disease outbreak in Bundibugyo has now been confirmed to be Ebola disease," Dr. Sam Zaramba, the Ugandan Health Ministry's director of health services, said in a statement.
Genetic analysis of samples taken from some of the victims shows it is a previously unknown type of Ebola, Dr. Tom Ksiazek of the U.S. Centers for Disease Control and Prevention said.
"This virus didn't behave as would be expected of some of the known strains," Ksiazek said in a telephone interview. "That tipped us off that this is probably a novel or new strain of Ebola."
Ugandan health officials have said that the virus appears to be unusually mild, but Ksiazek said it is not yet clear whether this is the case. He said experts need to check to see how many diagnosed patients are still alive.
"It's definitely a different strain. There's not much bleeding -- most died of fever," said Dr. Sam Okware, head of Uganda's national hemorrhagic fever task force.
"From the beginning we've been isolating cases ... but we can't say it's contained. There may be other people in those villages unknown to us," Okware said.
Ebola is a hemorrhagic fever, meaning it 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.
There are four identified strains of Ebola, Ksiazek said. The two strains that cause the most human disease are the Zaire and Sudan strains, named after the countries in which they first appeared.
A strain called Reston caused an outbreak in a primate facility in the Washington, D.C. suburb of the same name, while a single human case in Ivory Coast was caused by the Cote d'Ivoire strain.
The Zaire strain killed 80 percent of victims while the Sudan strain had just over a 50 percent mortality rate.
The new strain would be the fifth identified. Ksiazek said it had not yet been named.
Uganda was last hit by an epidemic of Ebola in 2000, when 425 people caught it and just over half of them died.
An outbreak in neighboring Congo this year infected up to 264 people, killing 187, the World Health Organization says.
Ugandan health officials originally suspected Marburg, a close Ebola cousin that infected three people in a different part of western Uganda the month before, killing one.
But samples had tested negative.
The government said it was taking steps to prevent the epidemic from spreading further.
"A response team is being strengthened to conduct contact tracing and public education ... All close contacts of the suspected cases are being closely followed up," Zaramba said.
(Additional reporting by Maggie Fox in Washington; editing by Stuart Grudgings)