Scientists say that the Ebola virus that has killed scores of people this year in Guinea is a new strain. That means it did not spread there from outbreaks in some other African nations.

Researchers do not know the source of the virus. Some other outbreaks have been linked to African fruit bats.

Ebola causes internal bleeding and organ failure and is fatal in up to 90 percent of cases. It spreads through direct contact with infected people. Knowing that the virus was not imported may help doctors control the outbreak, which has killed more than 120 people since December in West Africa, mostly in Guinea.

The report was published online Wednesday in the New England Journal of Medicine.