The WHO says there are an estimated 220 deaths, with more than 930 suspected cases.
Quarantines and travel bans won't limit the spread of the virus, which spreads through bodily fluids.
The global risk, however, remains low, the WHO says.
All travel restrictions are in place for 30 days.
The WHO estimates the case-fatality rate of Bundibugyo at around 40%.
The current DR Congo outbreak is caused by the Bundibugyo Ebola strain, which was not the causative lineage in the studies included in the analysis.
There are at least 500 suspected cases, including 130 deaths, so far in the outbreak.
Six other Americans are in the process of being evacuated.
Officials say 246 suspected cases and 65 deaths have been reported in the eastern part of the country.
A case study found indications of Ebola virus in breast milk 14 weeks after recovery, even as blood tests were negative.
