The UN World Health Organization says the death toll from the Ebola outbreak in West Africa has risen to at least 135 – 122 deaths in Guinea, where the outbreak is believe to have originated, while another 13 deaths had been reported by Liberian health officials.

Officials are investigating more than 200 suspected or confirmed cases of the virus in Guinea, Liberia and Sierra Leone.  Six suspected cases in Mali tested negative and no new suspected cases have been reported.

A report in the New England Journal of Medicine says the West African Ebola Outbreak is being caused by a new strain of the virus that did not spread there from other regions of Africa.  It was previously believed to be from the Zaire strain.

“The source of the virus is still not known,” said Doctor Stephan Gunther of the Bernhard Nocht Institute for Tropical Medicine in Hamburg, Germany.

The researchers also say the outbreak probably began in December, but went undetected.  They believe it made the jump to humans from some animal in the region.  Guinea earlier banned the sale and consumption of fruit bats, because earlier outbreaks were attributed to bushmeat.

Ebola is spread via bodily fluids from the infected source.  The incubation period is about 21 days.  There is no vaccine, no known cure, and is fatal in up to 90 percent of cases.